Yuvraj Ias: Gist Of Physical & World Geography

YUVRAJ IAS

GIST OF PHYSICAL & WORLD GEOGRAPHY A Quick Way To Cover And Revise The Syllabus

FOR UPSC CIVIL SERVICES PREPARATION

Copyright © 2019 Yuvraj IAS All Rights Reserved. This Book Or Any Portion Thereof May Not Be Reproduced Or Used In Any Manner Whatsoever Without The Express Written Permission Of The Publisher Except For The Use Of Brief Quotations In A Book Review. Published By: Global Pro Publications Chandigarh, Punjab, India Email: [email protected] Sold By: Global Pro Sellers Chandigarh, Punjab www.yuvrajias.com

Table Of Contents

What is Geography?................................................................................................................................ 3 Origin & Evolution Of Earth .................................................................................................................... 3 Structure Of The Earth ............................................................................................................................ 6 Continental Drift ..................................................................................................................................... 7 Earthquakes & Seismic Waves ................................................................................................................ 8 Volcanoes .............................................................................................................................................. 11 Volcanic Landforms ............................................................................................................................... 13 Air .......................................................................................................................................................... 14 Inside The Earth .................................................................................................................................... 15 Environment ......................................................................................................................................... 16 Major Landforms – Mountains, Plateaus, and Plains ........................................................................... 17 Major Domains of The Earth ................................................................................................................. 22 Motions of the earth: Rotation and Revolution ................................................................................... 24 MAPS ..................................................................................................................................................... 27 Latitudes & Longitudes ......................................................................................................................... 28 Standard Time and Time Zones ............................................................................................................ 29 Celestial Bodies ..................................................................................................................................... 30 Mass movements .................................................................................................................................. 32 Geomorphic processes.......................................................................................................................... 33 Weathering ........................................................................................................................................... 33 Significance Of Weathering................................................................................................................... 34 Biological Weathering ........................................................................................................................... 35 Physical Weathering ............................................................................................................................. 35 Chemical Weathering............................................................................................................................ 37 Exogenic processes ............................................................................................................................... 38 Endogenic Process ................................................................................................................................ 39

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Factors Controlling Temperature Distribution...................................................................................... 40 Composition and Structure of the Earth’s Atmosphere ....................................................................... 41 General circulation of the Atmosphere ................................................................................................ 44 Heating and Cooling of atmosphere ..................................................................................................... 45 Atmospheric Pressure ........................................................................................................................... 46 Tropical Cyclones .................................................................................................................................. 47 The Rock Cycle ...................................................................................................................................... 49 Forces Affecting the Velocity and Direction of Wind............................................................................ 50 The Nitrogen Cycle ................................................................................................................................ 51 The Oxygen Cycle .................................................................................................................................. 51 The Carbon Cycle .................................................................................................................................. 52 Biogeochemical Cycles .......................................................................................................................... 52 Salinity Of Ocean Water ........................................................................................................................ 53 Horizontal And Vertical Distribution Of Salinity ................................................................................... 54 Koeppen’s Climate Classification .......................................................................................................... 55 Climate Change ..................................................................................................................................... 57 The Hydrologic Cycle ............................................................................................................................. 58 Ocean Waves ........................................................................................................................................ 60 Clouds.................................................................................................................................................... 61 Evaporation And Condensation ............................................................................................................ 65 Erosional landforms .............................................................................................................................. 66 Glacial Depositional Landforms ............................................................................................................ 67 Glacial Erosional Landforms .................................................................................................................. 68 Types of Rainfall .................................................................................................................................... 69 Elements, Minerals and Rocks .............................................................................................................. 70 Minor Relief of the Ocean floor ............................................................................................................ 74 Ocean Floor And Its Features ................................................................................................................ 76

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What is Geography? ➢ ➢ ➢ ➢ ➢ ➢ ➢

The term geography was first devised by Eratosthenes, a Greek scholar (276-194 BC.) Geography is a discipline of the combination of spatial synthesis and temporal synthesis. According to geography, Earth is described as the abode of human beings. Landforms provide the foundation on which anthropogenic activities are placed. The plains are used for agriculture. Plateaus provide a platform for minerals and forest. Mountains make available space for meadows, forests, tourist spots, etc. They are regarded as the sources of rivers. Branches of Geography

➢ Physical Geography ➢ Human Geography ➢ Biogeography Physical Geography ➢

Geomorphology is a branch of Geography dealing with the study of landforms, the formation of landforms, and associated courses.

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Climatology includes the study of atmosphere structure, elements of weather, climate, climatic types and climatic regions.

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Hydrology deals with the study of water present on the surface of the earth comprising oceans, rivers, lakes and other water bodies, its influence on various life forms on earth and allied activities.

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Soil Geography is to study the courses of soil formation, types of soil, fertility status of soils, soil distribution and utilization. Origin & Evolution Of Earth Early Theories Nebular Hypothesis ➢ Immanuel Kant, a German philosopher gave this theory. ➢ In 1796, a mathematician Pierre-Simon Laplace reexamined it. ➢ According to this hypothesis, the planets were moulded out of a cloud of material associated with a young sun, which was rotating slowly. ➢ Binary theories ➢ As per these theories, the sun had a companion. ➢ Revised Nebular Hypothesis ➢ Revised Nebular Hypothesis was propounded by Carl Weizascar in Germany and Otto Schmidt in Russia. ➢ They regarded that a solar nebula surrounded the sun and that the nebula comprised of chiefly hydrogen, helium and something called dust.

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➢ The collision of particles and the friction caused a disk-shaped cloud to be formed and then the planets were created via the accretion process. Modern theories Big Bang Theory ➢

Alternatively called the expanding universe hypothesis.

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As per this theory, in the beginning, all matter or substance forming this universe existed at one place as a tiny ball. This tiny ball had an extremely small volume, infinite density and temperature.

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At the Big Bang, this ball blasted fiercely and forcefully and started a substantial process of expansion which continues to this day.

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Now it is accepted that this event took place 13.7 billion years ago.

Origin of Earth Formation of Planets The following are regarded as the stages in the planets’ development: ➢

The stars are localised gas lumps inside a nebula.

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A core to the gas cloud as well as a spinning disc of dust and gas are created because of the gravitational force within the lumps.

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After this, the cloud of gas condenses and the matter over the core is changed into tiny rounded objects.

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These small round objects develop into what are called planetesimals by a cohesion process.

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The smaller objects start forming larger bodies by colliding with one another and they stick together because of gravitational force.

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In the last stage, these large number of small planetesimals aggregate to develop into a smaller number of large bodies called planets.

Lightyear •

It is a unit of astronomical distance which is equal to the distance light travels in one year.

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A light year is a measure of distance and not of time.

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Light travels at a speed of 300,000 km/second.

Solar system •

Solar system consists of eight planets.

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Mercury, Venus, Earth, Mars, Jupiter, Uranus, Saturn and Neptune.

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The inner planets are Mercury, Venus, Earth, and Mars.

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After an asteroid belt come the outer planets, Jupiter, Saturn, Uranus, and Neptune.

The Moon •

The moon is the only natural satellite of the earth.

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Evolution of the Earth •

The age of Earth is approximately one-third of the age of the universe.

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Earth formed around 4.54 billion years ago by accretion from the solar nebula.

Lithosphere, Atmosphere, and Hydrosphere of the Earth •

Lithosphere: The firm outer part of the earth, comprising of the crust and upper mantle.

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Atmosphere: A layer of gases encircling a planet that is seized in place by the gravity of that body.

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Hydrosphere: It is the collective mass of water found on, under, and above the surface of the earth.

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The first stage of the evolution of Lithosphere, Atmosphere, and Hydrosphere is marked by the loss of primordial atmosphere.

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In the second stage, the hot interior of the earth contributed to the evolution of the atmosphere.

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Finally, the composition of the atmosphere was modified by the living world through the process of photosynthesis.

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The present composition of earth’s atmosphere is chiefly contributed by nitrogen and oxygen.

Geological Scale

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Structure Of The Earth •

The Crust

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The Mantle

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The Core

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The crust is the outermost solid part of the earth.

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It is fragile in nature.

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The thickness of the crust varies under the oceanic and continental areas.

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Oceanic crust is thinner as compared to the continental crust.

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The continental crust is thicker in the areas of major mountain systems.

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The crust made up of heavier rocks having a density of 3 g/cm3.

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The kind of rock seen in the oceanic crust is basalt.

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The mean density of material in the oceanic crust is 2.7 g/cm3.

The Crust

The Mantle •

The portion of the interior beyond the crust is called the mantle.

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It is in a solid state.

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It has a density higher than the crust portion.

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The thickness ranges from 10-200 km.

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The mantle extends from Moho’s discontinuity to a depth of 2,900 km.

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The asthenosphere is the upper portion of Mantle.

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It is the chief source of magma that finds its way to the surface during volcanic eruptions.

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The crust and the uppermost part of the mantle are called lithosphere.

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The Core •

The core-mantle boundary is positioned at the depth of 2,900 km.

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The inner core is in the solid state whereas the outer core is in the liquid state.

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The core is made up of very heavy material mostly constituted by nickel and iron. Hence it is also called the “nife” layer.

Continental Drift Continental Drift Theory •

Continental drift theory was proposed by Alfred Wegener in 1912.

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The theory deals with the distribution of the oceans and the continents.

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According to Wegener’s Continental Drift theory, all the continents were one single continental mass (called a Super Continent) – Pangaea and a Mega Ocean surrounded this supercontinent. The mega ocean is known by the name Panthalassa.

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The supercontinent was named Pangaea and the Mega-ocean was called Panthalassa.

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According to this theory, the supercontinent, Pangaea, began to split some two hundred million years back.

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Pangaea first split into 2 big continental masses known as Gondwanaland and Laurasia forming the southern and northern modules respectively.

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Later, Gondwanaland and Laurasia continued to break into several smaller continents that exist today.

Evidence supporting the Continental Drift Theory 1. The Matching of Continents (Jig-Saw-Fit) •

The coastlines of South America and Africa fronting each other have a remarkable and unique match.

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In 1964, Bullard created a map using a computer program to find the right fit of the Atlantic margin and it proved to be quiet.

2. Rocks of the Same Age across the Oceans •

The radiometric dating methods have helped in correlating the formation of rocks present in different continents across the ocean.

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The ancient rocks belts in the coast of Brazil match with those found in Western Africa.

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The old marine deposits found in the coasts of South America and Africa belong to the Jurassic Age. This implies that the ocean never existed before that time.

3. Tillite •

It is the sedimentary rock made from glacier deposits.

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The Gondwana system of sediments from India is recognized as having its counterparts in 6 different landmasses in the Southern Hemisphere.

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Counterparts of this series are found in Madagascar, Africa, Antarctica, Falkland Island, and Australia not to mention India.

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At the base, the system has thick tillite signifying widespread and sustained glaciation. 7

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Generally, the similarity of the Gondwana type sediments evidently shows that these landmasses had exceptionally similar origins.

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The glacial tillite gives a clear evidence for palaeoclimates and the drifting of continents.

4. Placer Deposits •

The presence of abundant placer deposits of gold along the Ghana coast and the complete lack of its source rocks in the area is a phenomenal fact.

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The gold-bearing veins are present in Brazil and it is evident that the gold deposits of Ghana in Africa are obtained from the Brazil plateau from the time when the two continents were beside each other.

5. Distribution of Fossils •

The interpretations that Lemurs occur in India, Africa and Madagascar led to the theory of a landmass named “Lemuria” connecting these 3 landmasses.

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Mesosaurus was a tiny reptile adapted to shallow brackish water.

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The skeletons of these creatures are found in the Iraver formations of Brazil and Southern Cape Province of South Africa.

Force for Drifting •

Wegener proposed that the movement accountable for the drifting of the continents was instigated by tidal force and pole-fleeing force.

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The polar-fleeing force relates to the rotation of the earth.

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The shape of earth

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The second force that was proposed by Wegener, the tidal force.

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Though, most of the scholars considered these forces to be totally insufficient.

Earthquakes & Seismic Waves •

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An earthquake is the shaking or trembling of the earth’s surface, caused by the sudden movement of a part of the earth’s crust. They result from the sudden release of energy in the Earth’s crust that creates seismic waves or earthquake waves. About 50,000 earthquakes large enough to be noticed without the aid of instruments occur annually over the entire Earth. Of these, approximately 100 are of sufficient size to produce substantial damage if their centers are near areas of habitation.

Terms associated with earthquakes Focus •

The place of origin of an earthquake inside the earth.

Epicenter • •

Point on the earth’s surface vertically above the focus. Maximum damage is caused at the epicenter.

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Wave Velocity •

5 to 8 km per second through the outer part of the crust but travel faster with depth.

Isoseismic Line •

A line connecting all points on the surface of the earth where the intensity is the same.

Causes of Earthquakes • • •

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Most earthquakes are causally related to compressional or tensional stresses built up at the margins of the huge moving lithospheric plates. The immediate cause of most shallow earthquakes is the sudden release of stress along a fault, or fracture in the earth’s crust. Sudden slipping of rock formations along faults and fractures in the earth’s crust happen due to constant change in volume and density of rocks due to intense temperature and pressure in the earth’s interior. Volcanic activity also can cause an earthquake but the earthquakes of volcanic origin are generally less severe and more limited in extent than those caused by fracturing of the earth’s crust. Earthquakes occur most often along geologic faults, narrow zones where rock masses move in relation to one another. The major fault lines of the world are located at the fringes of the huge tectonic plates that make up Earth’s crust. Plate tectonics: Slipping of land along the fault line along, convergent, divergent and transform boundaries cause earthquakes. Example: San Andreas Fault is a transform fault where Pacific plate and North American plate move horizontally relative to each other causing earthquakes along the fault lines.

Human Induced Earthquakes • •

Some earthquakes are human induced. Earthquakes in the reservoir region, mining sites etc. are human induced.

Some Earthquake inducing human activities • • • • • • •

Deep mining Underground nuclear tests Reservoir induced seismicity (RIS) Extraction of fossil fuels Groundwater extraction Artificial induction In fluid injection, the slip is thought to be induced by premature release of elastic strain, as in the case of tectonic earthquakes, after fault surfaces are lubricated by the liquid.

Seismic Waves or Earthquake Waves • •

The slipping of land generates seismic waves and these waves travel in all directions. Earthquake is any sudden shaking of the ground caused by the passage of seismic waves through Earth’s rocks. (Earthquake is caused by vibrations in rocks. And the vibrations in rocks are produced by seismic waves) 9

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Seismic waves are produced when some form of energy stored in Earth’s crust is suddenly released, usually when masses of rock straining against one another suddenly fracture and “slip.”

Types of Seismic Waves • • • •

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Earthquake waves are basically of two types — body waves and surface waves. Body waves are generated due to the release of energy at the focus and move in all directions travelling through the body of the earth. Hence, the name body waves. The body waves interact with the surface rocks and generate new set of waves called surface waves. These waves move along the surface. The velocity of waves changes as they travel through materials with different elasticity (stiffness) (Generally density with few exceptions). The more elastic the material is, the higher is the velocity. Their direction also changes as they reflect or refract when coming across materials with different densities. There are two types of body waves. They are called P and S-waves.

1. Primary waves or P waves (longitudinal)(fastest) • • • • • • • •

Also called as the longitudinal or compressional waves. Analogous to sound waves. Particles of the medium vibrate along the direction of propagation of the wave. P-waves move faster and are the first to arrive at the surface. These waves are of high frequency. They can travel in all mediums. Velocity of P waves in Solids > Liquids > Gases. Their velocity depends on shear strength or elasticity of the material.

2. Secondary waves or S waves (transverse)(least destructive) • • • • • •

Also called as transverse or distortional waves. Analogous to water ripples or light waves. S-waves arrive at the surface with some time lag. A secondary wave cannot pass through liquids or gases. These waves are of high frequency waves. Travel at varying velocities (proportional to shear strength) through the solid part of the Earth’s crust, mantle.

3. Surface waves or L waves (transverse)(slowest)(most destructive) • • • • • • •

Also called as long period waves. They are low frequency, long wavelength, and transverse vibration. Generally affect the surface of the Earth only and die out at smaller depth. Develop in the immediate neighborhood of the epicenter. They cause displacement of rocks, and hence, the collapse of structures occurs. These waves are the most destructive. Recoded last on the seismograph.

Earthquakes based on the depth of Focus •

Wadati Benioff zone is a zone of subduction along which earthquakes are common.

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• • • • • • • • • •

A Wadati–Benioff zone is a zone of seismicity corresponding with the down-going slab in a subduction zone (Convergent Boundary). Differential motion along the zone produces numerous earthquakes. Shallow focus earthquakes (most common at submarine ridges. Hardly felt) Intermediate focus earthquakes (somewhat severe) Deep focus earthquakes (Occurs at trenches – convergent boundary. Very powerful. Japan lies along trench line. Hence it faces devastating earthquakes). Shallow focus earthquakes are called crustal earthquakes as they exist in the earth’s crustal layer. Deep focus earthquakes are known as intra plate earthquakes, as they are triggered off by collision between plates. Shallow-focus earthquakes occur at depths less than 70 km, while deep-focus earthquakes occur at greater focal depths of 300 – 700 km. Shallow focus earthquakes are found within the earth’s outer crustal layer, while deep focus earthquakes occur within the deeper subduction zones of the earth. Shallow focus earthquakes are of smaller magnitudes, of a range 1 to 5, while deep focus earthquakes are of higher magnitudes, 6 to 8 or more.

Effects of Earthquakes • • • • •

Earthquakes cause landslides, damming of rivers, depressions which form lakes. They can cause submergence and emergence of landforms along coastal regions. Example: Coastline of Kutch. Lead to change in surface drainage and underground circulation of water. More devastating features of earthquakes are fires and seismic waves (tsunamis). Formation of cracks or fissures especially in the region of the epicenter is common.

Measurement All earthquakes are different in their intensity and magnitude. The instrument for measurement of the vibrations is known as Seismograph. Magnitude scale •

Richter scale is used to measure the Magnitude of the earthquake

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The energy released during a quake is expressed in absolute numbers of 0-10.

Intensity scale •

The mercalli scale is used to measure the intensity of an earthquake

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It measures the visible damage caused due to the quake.

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It is expressed in the range of 1-12.

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A volcano is a vent or fissure in Earth’s crust through which lava, ash, rocks, and gases erupt.

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An active volcano is a volcano that has erupted in the recent past.

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The mantle contains a weaker zone known as asthenosphere.

Volcanoes Volcanoes

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Magma is the material present in the asthenosphere.

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Material that flows to or reaches the ground comprises lava flows, volcanic bombs, pyroclastic debris, dust, ash and gases. The gases maybe sulphur compounds, nitrogen compounds, and trace amounts of argon, hydrogen and chlorine.

Types of Volcanoes •

Volcanoes are classified on the basis of nature of eruption and the form developed at the surface.

Shield Volcanoes •

The Shield volcanoes are the largest of all the volcanoes on the earth, which are not steep.

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These volcanoes are mostly made up of basalt.

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They become explosive if in some way water gets into the vent, otherwise, they are characterized by low-explosivity.

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The lava that is moving upwards does so in a fountain-form and emanates the cone at the vent’s top and then develops into cinder cone.

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Eg: Hawaiian shield volcanoes

Composite Volcanoes •

Composite Volcanoes are characterized by outbreaks of cooler and more viscous lavas than basalt.

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They are constructed from numerous explosive eruptions.

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Large quantities of pyroclastic material and ashes find their way to the ground along with lava.

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This material gathers near the vent openings resulting in the creation of layers.

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Mayon Volcano in the Philippines, Mount Fuji in Japan, and Mount Rainier in Washington are the major composite volcanoes in the world.

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The major composite volcano chains are Pacific Rim which known as the “Rim of Fire”.

Caldera •

Calderas are known as the most explosive volcanoes of Earth.

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They are generally explosive in nature.

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When they erupt, they incline to collapse on themselves rather than constructing any structure.

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The collapsed depressions are known as calderas.

Flood Basalt Provinces •

Flood Basalt Province volcanoes discharge highly fluid lava that flows for long distances.

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Many parts of the world are covered by thick basalt lava flows.

Mid-Ocean Ridge Volcanoes •

These volcanoes are found in the oceanic areas.

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There exists a system of mid-ocean ridges stretching for over 70000 km all through the ocean basins. 12

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The central region of this ridge gets frequent eruptions.

Volcanic Landforms Volcanic Landforms Volcanic eruptions result in the formation of landforms and here we are going to discuss volcanic landforms. Intrusive Forms •

The lava that is discharged during volcanic eruptions on cooling develops into igneous rocks.

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The cooling may take place either on arriving on the surface or also while the lava is still in the crustal portion.

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According to the location of the cooling of the lava, igneous rocks are categorized as plutonic rocks and volcanic rocks.

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The lava that cools inside the crustal portions takes diverse forms. These forms are called intrusive forms.

Some of the forms are shown in Figure given below

Batholiths •

Batholiths are the cooled portion of magma chambers.

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It is a large body of magmatic material that cools in the deeper depth of the crust moulds in the form of large domes.

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They appear on the surface only after the denudation processes eliminate the overlying materials.

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These are granitic bodies.

Laccoliths •

These are large dome-shaped intrusive bodies with a level base and linked by a pipelike channel from below.

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It bears a similarity to the surface volcanic domes of the composite volcano, only these are located at deeper depths.

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It can be considered as the localized source of lava

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The Karnataka plateau is patterned with dome hills of granite rocks.

Lopolith •

When the lava moves upwards, a part of the same tends to move in a horizontal direction wherever it finds a weak plane.

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It can get rested in various forms. If it develops into a saucer shape, concave to the sky body, it is called lopolith.

Phacolith •

It is a wavy mass of intrusive rocks found at the base of synclines or at the top ofthe anticline in the folded igneous country.

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These wavy materials have a definite outlet to source beneath in the form of magma cavities.

Sills •

The near horizontal bodies of the intrusive igneous rocks are called sill

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The thick horizontal deposits are called sills whereas the thinner ones are called sheets.

Dykes •

Dykes are the most commonly found intrusive forms in the western Maharashtra area.

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When the lava makes its channel through cracks and the fissures, it solidifies almost perpendicular to the ground.

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This gets cooled in the same position to grow a wall-like structure. Such structures are known as dykes.

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These are regarded as the feeders for the eruptions that led to the development of the Deccan traps.

Air COMPOSITION OF THE ATMOSPHERE •

Nitrogen-is the most plentiful gas in the air.

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Plants need nitrogen for their survival.

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Oxygen- is the second most abundant gas in the air.

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Humans and animals take oxygen from the air as they inhale.

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Carbon dioxide- is another most important gas.

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Green plants use carbon dioxide to make their food and release oxygen.

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Argon

STRUCTURE OF THE ATMOSPHERE

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Our atmosphere is divided into five layers starting from the earth’s surface. •

Troposphere-the most important layer of the atmosphere. Its average height is 13 km. The air we inhale exists here. Most weather phenomena like rainfall, hailstorm, etc. occur in this layer.

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Stratosphere- just above the troposphere lies the stratosphere. It extends up to a height of 50 km. Being free from associated weather phenomenon, this layer is most ideal for flying aeroplanes. Contains ozone.

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Mesosphere-: This is the next & third layer of the atmosphere. It lies above the stratosphere. It extends up to the height of 80 km.

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Thermosphere -In thermosphere temperature rises very rapidly with increasing height. Ionosphere is a part of this sphere. It extends between80-400 km. This layer helps in radio communications.

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Exosphere-The last & upper most layer of the atmosphere is known as exosphere.

WEATHER AND CLIMATE •

Weather is day to day condition of the atmosphere.

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The average weather condition of a place for a longer period of time represents the climate of a place.

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Temperature-The degree of hotness and coldness of the air (body) is known as temperature.

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Air Pressure-is defined as the pressure exerted by the weight of air on the earth’s surface.

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Wind-The movement of air from high pressure area to low pressure areas is called wind.

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Winds can be broadly divided into three types •

Permanent winds – The trade winds, easterlies and westerlies are the permanent winds. They blow throughout the year constantly in a particular direction.

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Seasonal winds – These winds change their direction in different seasonsexample monsoon winds in India.

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Local winds – These winds blow only during a certain period of the day or year in a small area. For example, land breeze and sea breeze. – Ex-hot and dry local wind of northern plains of India is called loo.

Inside The Earth Inside The Earth •

The earth, is a dynamic planet.

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It is constantly undergoing changes inside and outside.

Interior of the Earth •

The earth is made up of several concentric layers with one inside another.

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Crust-

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The uppermost layer over the earth’s surface. 15

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It is the thinnest of all the layers.

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It is about 35 km. on the continental masses and only 5 km. on the ocean floors.

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The main mineral constituents of the continental mass are silica and alumina. It is thus called si-al (si-silica and al-alumina)

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The oceanic crust mainly consists of silica and magnesium; it is therefore called sima (si-silica and ma-magnesium)

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Mantle-

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Just beneath the crust is the mantle which extends up to a depth of 2900 km.

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Core-

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The innermost layer is the core with a radius of about 3500 km.

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It is mainly made up of nickel and iron and is called nife (ni – nickel and fe – ferrous i.e. iron).

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The central core has very high temperature and pressure.

Rocks and Minerals •

The earth’s crust is made up of various types of rocks.

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Rock- Any natural mass of mineral matter that makes up the earth’s crust.

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There are three major types of rocks-

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Igneous rocks-when the molten magma cools; it solidifies to become igneous rock.

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Sedimentary rocks- igneous rocks are broken down into small particles that are transported and deposited to form sedimentary rocks.

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Metamorphic rocks- When the igneous and sedimentary rocks are subjected to heat and pressure they change into metamorphic rocks.

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Rocks are made up of different minerals.

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Minerals- are naturally occurring substances which have certain physical properties and definite chemical composition.

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Minerals are very important to humankind. Some are used as fuels. For example, coal, natural gas and petroleum. They are also used in industries – iron, aluminium, gold, uranium, etc, in medicine, in fertilisers, etc.

Environment •

The place, people, things and nature that surround any living organism is called environment.

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It is a combination of natural and human-made phenomena.

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The natural environment refers to both biotic and abiotic conditions existing on the earth. •

Biotic- The world of living organisms. E.g. plants and animals.

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Abiotic- The world of non-living elements. E.g. land.

Natural Environment Lithosphere •

It is the solid crust or the hard top layer of the earth. It is made up of rocks and minerals and covered by a thin layer of soil. 16

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Lithosphere is the domain that provides us forests, grasslands for grazing, land for agriculture and human settlements. It is also a source of mineral wealth.

Hydrosphere •

The domain of water is referred to as hydrosphere

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It comprises various sources of water and different types of water bodies like rivers, lakes, seas, oceans, etc.

Atmosphere •

It is the thin layer of air that surrounds the earth.

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The gravitational force of the earth holds the atmosphere around it.

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It protects us from the harmful rays and scorching heat of the sun.

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It consists of a number of gases, dust and water vapour. The changes in the atmosphere produce changes in the weather and climate.

Biosphere •

Plant and animal kingdom together make biosphere.

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It is a narrow zone of the earth where land, water and air interact with each other to support life.

What is ecosystem? •

All plants, animals and human beings depend on their immediate surroundings. This relation between the living organisms, as well as the relation between the organisms and their surroundings, forms an ecosystem.

Major Landforms – Mountains, Plateaus, and Plains Mountains • • •

Nearly 27% of the world’s land surface is covered by mountains. It is from the mountains that up to 80% of the planet’s fresh surface water come from. According to the UN’s Food and Agriculture Organization (FAO), about 12% of the world’s population lives in the mountains, but over 50% are directly or indirectly dependent on mountain resources.

CLASSIFICATION OF MOUNTAINS The mountains, on the basis of their mode of formation, can be classified as: 1. 2. 3. 4.

Fold Mountains Block Mountains Volcanic Mountains/ Accumulated Mountains Residual Mountains/ Relict Mountains

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Fold Mountains • • • • •

Mountain ranges mainly consisting of uplifted folded sedimentary rocks are called Fold Mountains. They are formed due to the force of compression arising from the endogenicor internal forces. Synclines (trough) and anticlines (crest) are part of Fold Mountains. The Himalayas in Asia, the Alps in Europe, the Rockies in North America, and the Andes in South America are the most prominent fold mountains of the world. Since these mountain ranges were formed during the most recent mountain building period, they are also known as Young Fold Mountains.

Block Mountains • • •

Block Mountains are also formed by the internal or endogenic earth movements which cause the force of tension and faulting. The down-lifting or uplifting of land in between two parallel faults results in the formation of Block Mountains. A block mountain is also called as Horst and the rift valley formed as a result of faulting is called Graben.

Volcanic Mountains or Accumulated Mountains • •

The mountains formed by the accumulation of volcanic materials are called as Volcanic Mountains or Mountains of accumulation. Examples: Mount Mauna Loa in Hawaii Island, Mount Popa in Myanmar, Fuji Yama in Japan etc are some examples.

Residual Mountains or Relict Mountains • • • • •

We have seen the effects of weathering (as part of exogenic processes). Weathering acts upon the earth’s crust constantly. To a large extent, the process of wearing down depends on the shape and structure of the rocks upon which it acts. So, in some cases, some portions of an elevated area escape from the process of weathering due to the hardness of the materials it is made of. These portions remain unweathered while its surrounding area gets eroded constantly. This results in the formation of Residual or Relict Mountains. Examples: Hills like Nilgiri, Palkonda, Parasnath and Rajmahal and Mountains like the Aravalli, the Vindhya, and the Satpura are some of the examples of Relict Mountains in India.

Economic Significance of Mountains •

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A storehouse of resources: Mountains are the storehouse of natural resources. Large resources of minerals like petroleum, coal, limestone are found in mountains. The mountains are the main source of timber, lac, medical herbs, etc. Generation of hydro-electricity: Hydro-electricity is mainly generated from the waters of perennial rivers in the mountains. 18

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An abundant source of water: Perennial rivers arising in the snow-fed or heavily rainfed mountains are one of the important sources of water. They help in promoting the irrigation and provide water for many other purposes. Formation of fertile plains: The rivers that originate from the high mountain ranges bring silt along with water to the lower valleys. This helps in the formation of fertile plains and further the expansion of agriculture and related activities. Natural political frontiers: The mountains can also act as natural boundaries between the two countries. They have a prominent role in protecting the country from external threats. Effects on climate: They serve as a climatic divide between two adjoining regions. The mountains cause orogenic rainfalls, diversion, and blocking of cold winds, etc. Tourist centres: The pleasant climate and beautiful sceneries of the mountains have led to their development as centres of tourist attraction.

Plateaus • • •

A plateau is an elevated area with a more or less levelled land on its top. It has a large area on its top and a steep slope on its sides. They are also called as high plains or tablelands. The plateaus cover about 18% of the earth’s land surface.

CLASSIFICATION OF PLATEAUS On the basis of their geographical location and structure of rocks, the plateaus can be classified as: 1. 2. 3. 4. 5.

Intermontane Plateaus Piedmont plateaus Continental plateaus Volcanic plateaus Dissected plateaus

Intermontane Plateaus • • • • •

The plateaus which are bordering the mountain ranges (generally fold mountains) or are partly or fully enclosed within them are the intermontane plateaus. The word ‘intermontane’ means ‘between mountains’. Intermontane plateaus are the highest in the world. They have nearly horizontal rock layers which are raised to very heights by vertical movements of the earth. Examples: The Plateau of Tibet is an example of the intermontane plateau which is surrounded by the fold mountains like the Himalayas, the Karakoram, the Kunlun and the Tien Shah.

Piedmont Plateaus • •

Plateaus which is situated at the foot of a mountain and is locked on the other side by a plain or a sea/ ocean is called as a piedmont plateau. The word ‘piedmont’ means ‘foot of a mountain’.

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They are also called as Plateaus of denudation as the areas once were high to the level of mountains, have now been reduced to the foot level of the mountain by various agents of erosion. Examples: The Malwa Plateau is an example of piedmont plateau.

Continental Plateaus •

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They are formed either by an extensive continental upliftment or by the spread of horizontal basic lava (less viscous) sheets completely covering the original topography. This kind of plateaus shows an abrupt elevation in contrast to the nearby lowland or sea (i.e. more steepness on sides). The Continental Plateaus are also known as Plateaus of Accumulation. Examples: Plateau of Maharashtra is an example of the continental plateau.

Volcanic Plateaus • • •

A volcanic plateau is a plateau produced by volcanic activity. There are two main types: lava plateaus and pyroclastic plateaus. Lava plateaus are formed by highly fluid basaltic lava during numerous successive eruptions through numerous vents without violent explosions. Pyroclastic volcanic plateaus are produced by massive pyroclastic flows and they are underlain by pyroclastic rocks.

Dissected Plateaus • •

A dissected plateau is a plateau area that has been severely eroded so that the relief is sharp. Such an area may appear as mountainous. Dissected plateaus are distinguishable from orogenic mountain belts by the lack of folding, metamorphism, extensive faulting, or magmatic activity that accompanies orogeny (mountain building).

The economic significance of Plateaus •

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A storehouse of minerals: Most of the minerals in the world are found in plateaus. The extraction of minerals in plateaus is relatively easier on plateaus than mountains. The major portions of industrial raw materials are obtained from plateaus. We get gold from the plateau of Western Australia; copper, diamond and gold from the plateaus of Africa; and coal, iron, manganese and mica from the Chottanagpur Plateau in India. Generation of hydel-power: The edges of plateaus form waterfalls which provide ideal sites for generating hydel power. Cool climate: The higher parts of the plateaus even in tropical and sub-tropical regions have a cool climate. Animal rearing and agriculture: plateaus have large grassland areas suitable for animal rearing especially sheep, goat, and cattle. The lava plateaus when compared to other plateaus are richer in minerals and hence used for agriculture as the soil is very fertile.

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Plains • • • • •

Plains are the most important landforms found on the earth surface. A plain is nothing but a low-lying relatively flat land surface with very gentle slope and minimum local relief. About 55% of the earth’s land surface is occupied by plains. Most of the plain have been formed by deposition of sediments brought down by rivers. Besides rivers, some plains have also been formed by the action of the wind, moving ice and tectonic activities (Refer exogenic processes).

CLASSIFICATION OF PLAINS On the basis of their mode of formation, plains can be classified as: 1. Structural plain 2. Erosional plains 3. Depositional plains Structural Plains • • •

These plains are mainly formed by the upliftment of a part of the sea floor or continental shelf. They are located on the borders of almost all the major continents. The structural plains may also be formed by the subsidence of areas.

Erosional Plains (Peneplains) • •

Erosional plains are formed by the continuous and longtime erosion of uplands. The surface of such plains is hardly smooth and hence, they are also called as Peneplains, which means almost plain.

Depositional Plains • • • • •

These plains are formed by the depositional activity of various geomorphic agents. When plains are formed by the river deposits, they are called as riverine or alluvial plains. The depositions of sediments in a lake give rise to a Lacustrine Plain or Lake Plains. The Valley of Kashmir is an example of lacustrine plain. When plains are formed by glacial deposits, they are called as Glacial or Drift Plains. When the wind is the major agent of deposition, those plains are called as Loess Plains.

The economic significance of Plains •

Fertile soil: The plains generally have deep and fertile soil. As they have a flat surface, the means of irrigation can be easily developed. That is why plains are called as the ‘Food baskets of the world’.

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The growth of industries: The rich agricultural resources, especially of alluvial plains, have helped in the growth of agro-based industries. Since the plains are thickly populated, plenty of labour is available for the intense cultivation and for supplying the workforce for the industries. Expansion of means of transportation: The flat surface of plains favours the building of roads, airports and laying down railway lines. Centres of civilizations: Plains are centres of many civilizations. Setting up of cities and towns: Easy means of transportation on land and the growth of agriculture and industries in plains have resulted in the setting up and expansion of cities and towns. The most developed trade centres and ports of the world are found in the plains only and as much as 80% of the world’s population lives here.

• • •

Major Domains of The Earth The earth’s surface is a complex zone in which the three major components of the environment meet, overlap and interact. The Four Domains of the Earth •

Lithosphere: The solid portion of the earth

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Atmosphere: The gaseous layers that surround the earth

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Hydrosphere: Water covers a very big area of the earth’s surface and this area is called the Hydrosphere

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Biosphere: It is the narrow zone where land, water and air together are found.

Lithosphere •

The solid portion of the earth is called the Lithosphere.

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It comprises the rocks of the earth’s crust and the thin layers of soil that contain nutrient elements which sustain organisms.

There are two main divisions of the earth’s surface: 1. Continents- the large landmasses. 2. Ocean basins- the huge water bodies. Continents There are seven major continents and these are separated by large water bodies. 1. Asia •

Asia is the largest continent covering one-third of the total land area of the earth.

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The continent lies in the Eastern Hemisphere.

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The Tropic of Cancer passes through Asia.

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The Ural mountains on the west separates from Europe.

2. Europe •

Europe is much smaller than Asia lying to the west of Asia.

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The Arctic Circle passes through it.

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Its three sides are bound by water bodies. 22

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3. Africa •

Africa is the second largest continent after Asia.

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A large part of Africa lies in the Northern Hemisphere.

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Africa is the only continent through which the Tropic of Cancer, the Equator and the Tropic of Capricorn pass.

4. North America •

North America is the third largest continent of the world.

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The continent lies completely in the Northern and Western Hemisphere.

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The Isthmus of Panama a narrow strip links North America and South America.

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This continent is surrounded by three oceans and they are the Atlantic Ocean, the Pacific Ocean, and the Arctic Ocean.

5. South America •

South America lies mostly in the Southern Hemisphere.

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It is surrounded by two oceans; the Pacific Ocean on the west and the Atlantic Ocean on the east and north.

6. Australia •

Australia is the smallest continent that lies entirely in the Southern Hemisphere.

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It is surrounded on all sides by the oceans and seas.

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It is called an island continent.

7. Antarctica •

Antarctica is a huge continent and lies completely in the Southern Hemisphere.

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The South Pole lies in the South Polar Region almost at the centre of this continent and is permanently covered with thick ice sheets.

Hydrosphere •

The earth is called the blue planet.

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More than 71 per cent of the earth is covered with water and 29 per cent is with land. Hydrosphere consists of water in all its forms.

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More than 97% of the Earth’s water is found in the oceans and is too salty for human use.

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Hydrosphere consists of water in all its forms like running water in oceans and rivers and in lakes, ice in glaciers, underground water and the water vapour in atmosphere.

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97% of the Earth’s water is found in the oceans and is too salty, the rest of the water is in the form of icesheets and glaciers or under the ground and a very small percentage is available as fresh water for human use

Oceans •

The three chief movements of ocean waters are the waves, the tides and the ocean currents.

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Oceans are the major part of hydrosphere and they are all interconnected.

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The five major oceans in order of their size are 23

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1. the Pacific Ocean: It is almost circular in shape. Asia, Australia, North and South Americas surround it. 2. the Atlantic Ocean: It is the second largest Ocean in the world. It is ‘S’ shaped. It is flanked by the North and South Americas on the western side, and Europe and Africa on the eastern side. 3. the Indian Ocean: It is the only ocean named after a country, that is, India. The shape of ocean is almost triangular. In the north, it is bound by Asia, in the west by Africa and in the east by Australia. 4. the Southern Ocean: It surrounds the continent of Antarctica 5. the Arctic Ocean: It is located within the Arctic Circle and surrounds the North Pole. The Berring strait a narrow stretch of shallow water connects it with the Pacific Ocean. Atmosphere The earth is surrounded by a layer of gas called the atmosphere. •

The atmosphere extends up to a height of about 1,600 kilometres.

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The atmosphere is divided into five layers based on composition, temperature and other properties and they are:

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1. the troposphere 2. the stratosphere 3. the mesosphere 4. the thermosphere 5. the exosphere A bout 99 per cent of clean and dry air in the atmosphere is composed mainly of nitrogen and oxygen. Nitrogen 78 per cent, oxygen 21 per cent and other gases like carbondioxide, argon and others comprise 1 per cent by volume.

Biosphere – The Domain of Life •

The biosphere is the narrow zone of contact between the land, water and air.

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It is the zone where life exists that makes this planet unique.

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The organisms in the biosphere are commonly divided into:

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1. the plant kingdom 2. the animal kingdom The three domains of the earth interact with each other and affect each other in some way or the other.

Motions of the earth: Rotation and Revolution Rotation of Earth • • • •

Earth rotates along its axis from west to east. It takes approximately 24 hrs to complete on rotation. Days and nights occur due to rotation of the earth. The circle that divides the day from night on the globe is called the circle of illumination.

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Earth rotates on a tilted axis. Earth’s rotational axis makes an angle of 23.5° with the normal i.e. it makes an angle of 66.5° with the orbital plane. Orbital plane is the plane of earth’s orbit around the Sun.

Why are days always longer than nights at the equator? • •

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If there was no atmosphere, there would be no refraction and the daytime and nighttime would be near equal at the equator, at least during equinoxes. But due to atmosphere, the sun’s rays gets refracted (bending of light). Refraction is particularly stronger during the morning and the evening time when the sun’s rays are slant. Even though the actual sun is below the horizon, its apparent image would appear above the horizon due to refraction. This makes the days longer than nights at the equator.

Why temperature falls with increasing latitude (as we move from equator towards poles)? • • •

Because of the spherical (Geoid) shape of the earth and the position of the sun. Because the energy received per unit area decreases from equator to poles. Because Equator receives direct sunlight while Poles receive slant or oblique rays of the Sun.

Revolution • •

The second motion of the earth around the sun in its orbit is called revolution. It takes 365¼ days (one year) to revolve around the sun. Six hours saved every year are added to make one day (24 hours) over a span of four years. This surplus day is added to the month of February. Thus every fourth year, February is of 29 days instead of 28 days. Such a year with 366 days is called a leap year.

Solstice • • • •

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On 21st June, the northern hemisphere is tilted towards the sun. The rays of the sun fall directly on the Tropic of Cancer. As a result, these areas receive more heat. The areas near the poles receive less heat as the rays of the sun are slanting. The north pole is inclined towards the sun and the places beyond the Arctic Circle experience continuous daylight for about six months. Since a large portion of the northern hemisphere is getting light from the sun, it is summer in the regions north of the equator. The longest day and the shortest night at these places occur on 21st June. At this time in the southern hemisphere all these conditions are reversed. It is winter season there. The nights are longer than the days. This position of the earth is called the summer solstice. On 22nd December, the Tropic of Capricorn receives direct rays of the sun as the south pole tilts towards it. As the sun’s rays fall vertically at the Tropic of Capricorn (23½° s), a larger portion of the southern hemisphere gets light. Therefore, it is summer in the southern hemisphere with longer days and shorter nights. The reverse happens in the northern hemisphere. This position of the earth is called the winter solstice.

Equinox

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• • •

On 21st March and September 23rd, direct rays of the sun fall on the equator. At this position, neither of the poles is tilted towards the sun; so, the whole earth experiences equal days and equal nights. This is called an equinox. On 23rd September, it is autumn season [season after summer and before the beginning of winter] in the northern hemisphere and spring season [season after winter and before the beginning of summer] in the southern hemisphere. The opposite is the case on 21st March, when it is spring in the northern hemisphere and autumn in the southern hemisphere. Thus, you find that there are days and nights and changes in the seasons because of the rotation and revolution of the earth respectively. Rotation === Days and Nights. Revolution === Seasons.

Why regions beyond the Arctic circle receive sunlight all day long in summer? • • •

This is because of the tilt of the earth. Earth’s axis at the north pole is tilted towards the sun in summer. So the whole of Arctic region falls within the ‘zone of illumination’ all day long in summer

Daylight saving in some temperate regions • •

Daylight saving time (DST) or summer time is the practice of advancing clocks during summer months by one hour. In DST, evening time is increased by sacrificing the morning hours.

[Normal days = Start office at 10 AM and close at 5 PM In DST = Advance clock by one hour (can be more) = Start office at 9 AM and Close at 4 PM] •

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Typically, users in regions with summer time (Some countries in extreme north and south) adjust clocks forward one hour close to the start of spring and adjust them backward in the autumn to standard time. Advantage: Putting clocks forward benefits retailing, sports, and other activities that exploit sunlight after working hours. Reduces evening use of incandescent lighting, which was formerly a primary use of electricity. Problems: DST clock shifts sometimes complicate timekeeping and can disrupt travel, billing, record keeping, medical devices, heavy equipment, and sleep patterns.

Variations in the length of daytime and night time from season to season are due to a. b. c. d.

the earth’s rotation on its axis the earth’s revolution round the sun in an elliptical manner latitudinal position of the place revolution of the earth on a tilted axis

Hint: Revolution + Rotation on a Tilted Axis = = Variation in seasons = = Variation in Day time and Night time

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MAPS Map is a representation or a drawing of the earth’s surface or a part of it on a flat surface according to a scale. Types of Maps Physical or Relief Maps •

Maps showing natural features of the earth such as mountains, plateaus, plains, rivers, oceans etc. are known as physical or relief maps.

Political Maps •

Maps showing cities, towns, villages, states, and different countries of the world with their boundaries are called political maps.

Thematic Maps •

Maps that focus on specific information like road maps, rainfall maps, distribution of forests, industries etc. are called thematic maps.

Sketch •

It is a drawing mainly based on memory and spot observation and not to scale

Plan •

It is a drawing of a small area on a large scale.

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A large-scale map gives a lot of information.

Components of Maps Distance •

Maps are drawings, which reduce the entire world or a part of it to fit on a sheet of paper. A scale is being used to do this accurately. A scale is a ratio between the actual distance on the ground and the distance shown on the map

Direction •

There are 4 cardinal points namely-North, South, East, West.

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Other four intermediate directions are north-east (NE), southeast(SE), south-west (SW) and north-west (NW)

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It is possible to locate any place more accurately with the help of these intermediate directions.

Symbols •

Different features such as buildings, roads, bridges, trees, railway lines or a well. So, they are shown by using certain letters, shades, colours, pictures and lines on the maps. These symbols give a lot of information in a limited space.

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With the use of these symbols, maps can be drawn easily and are simple to read.

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Latitudes & Longitudes • • •

Latitudes and Longitudes are imaginary lines used to determine the location of a place on earth. The shape of the earth is ‘Geoid’. And the location of a place on the earth can be mentioned in terms of latitudes and longitudes. Example: The location of New Delhi is 28° N, 77° E.

Latitude • • • •

Latitude is the angular distance of a point on the earth’s surface, measured in degrees from the center of the earth. As the earth is slightly flattened at the poles, the linear distance of a degree of latitude at the pole is a little longer than that at the equator. For example at the equator (0°) it is 68.704 miles, at 45° it is 69.054 miles and at the poles it is 69.407 miles. The average is taken as 69 miles (111km). 1 mile = 1.607 km.

Important parallels of latitudes • • • • •

Besides the equator (0°), the north pole (90°N) and the south pole (90° S), there are four important parallels of latitudes– Tropic of Cancer (23½° N) in the northern hemisphere. Tropic of Capricorn (23½° S) in the southern hemisphere. Arctic circle at 66½° north of the equator. Antarctic circle at 66½° south of the equator.

Latitudinal Heat zones of the earth •

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The mid-day sun is exactly overhead at least once a year on all latitudes in between the Tropic of Cancer and the Tropic of Capricorn. This area, therefore, receives the maximum heat and is called the torrid zone. The mid-day sun never shines overhead on any latitude beyond the Tropic of Cancer and the Tropic of Capricorn. The angle of the sun’s rays goes on decreasing towards the poles. As such, the areas bounded by the Tropic of Cancer and the Arctic circle in the northern hemisphere, and the Tropic of Capricorn and the Antarctic circle in the southern hemisphere, have moderate temperatures. These are, therefore, called temperate zones. Areas lying between the Arctic circle and the north pole in the northern hemisphere and the Antarctic circle and the south pole in the southern hemisphere, are very cold. It is because here the sun does not raise much above the horizon. Therefore, its rays are always slanting. These are, therefore, called frigid zones.

Longitude • • •

Longitude is an angular distance, measured in degrees along the equator east or west of the Prime (or First) Meridian. On the globe longitude is shown as a series of semi-circles that run from pole to pole passing through the equator. Such lines are also called Unlike the equator which is centrally placed between the poles, any meridian could have been taken to begin the numbering of longitude. It was finally decided in 1884, by

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• • •

international agreement, to choose as the zero meridian the one which passes through the Royal Astronomical Observatory at Greenwich, near London. This is the Prime Meridian (0°) from which all other meridians radiate eastwards and westwards up to 180°. As the parallels of latitude become shorter poleward, so the meridians of longitude, which converge at the poles, enclose a narrower space. They have one very important function, they determine local time in relation to G.M.T. or Greenwich Mean Time, which is sometimes referred to as World Time.

Longitude and Time • • • •

Since the earth makes one complete revolution of 360° in one day or 24 hours, it passes through 15° in one hour or 1° in 4 minutes. The earth rotates from west to east, so every 15° we go eastwards, local time is advanced by 1 hour. Conversely, if we go westwards, local time is retarded by 1 hour. We may thus conclude that places east of Greenwich see the sun earlier and gain time, whereas places west of Greenwich see the sun later and lose time. If we know G.M.T., to find local time, we merely have to add or subtract the difference in the number of hours from the given longitude.

Standard Time and Time Zones • •

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If each town were to keep the time of its own meridian, there would be much difference in local time between one town and the other. Travelers going from one end of the country to the other would have to keep changing their watches if they wanted to keep their appointments. This is impractical and very inconvenient. To avoid all these difficulties, a system of standard time is observed by all countries. Most countries adopt their standard time from the central meridian of their countries. In larger countries such as Canada, U.S.A., China, and U.S.S.R, it would be inconvenient to have single time zone. So these countries have multiple time zones. Both Canada and U.S.A. have five time zones—the Atlantic, Eastern, Central, Mountain and Pacific Time Zones. The difference between the local time of the Atlantic and Pacific coasts is nearly five hours. S.S.R had eleven time zones before its disintegration. Russia now has nine time zones.

The International Date Line • • •

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A traveler going eastwards gains time from Greenwich until he reaches the meridian 180°E, when he will be 12 hours ahead of G.M.T. Similarly in going westwards, he loses 12 hours when he reaches 180°W. There is thus a total difference of 24 hours or a whole day between the two sides of the 180° meridian. This is the International Date Line where the date changes by exactly one day when it is crossed. A traveler crossing the date line from east to west loses a day (because of the loss in time he has made); and while crossing the dateline from west to east he gains a day (because of the gain in time he encountered). The International Date Line in the mid-Pacific curves from the normal 180° meridian at the Bering Strait, Fiji, Tongaand other islands to prevent confusion of day and date in some of the island groups that are cut through by the meridian. Some of them keep Asiatic or New Zealand standard time, others follow the American date and time.

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Why is the international dateline drawn in a zigzag manner? • • •

The International Date Line (IDL) passes through the Pacific Ocean. It is an imaginary line, like longitudes and latitudes. The time difference on either side of this line is 24 hours. So, the date changes as soon as one crosses this line. Some groups of Islands (Polynesia, Melanesia, Micronesia) fall on either of the dateline. So if the dateline was straight, then two regions of the same Island Country or Island group would fall under different date zones. Thus to avoid any confusion of date, this line is drawn through where the sea lies and not land. Hence, the IDL is drawn in a zig-zag manner.

Indian Standard Time •

The Indian Government has accepted the meridian of 82.5° east for the standard time which is 5 hours 30 mins, ahead of Greenwich Mean Time.

Chaibagaan Time • • • • •

150 years ago British colonialists introduced “chaibagaan time” or “bagaan time”, a time schedule observed by tea planters, which was one hour ahead of IST. This was done to improve productivity by optimizing the usage of daytime. After Independence, Assam, along with the rest of India, has been following IST for the past 66 years. The administration of the Indian state of Assam now wants to change it’s time zone back to Chaibagaan time to conserve energy and improve productivity. Indian government didn’t accept to such a proposal.

Celestial Bodies •

Celestial bodies are objects like Sun, moon, stars and others that shine in the night sky.

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Some celestial bodies are very big and are made up of gases and heat. They have their own heat and light which is emitted in large amounts. These celestial bodies are called stars and our Sun is a star.

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The sun, the moon and all those shining objects in the night sky are called celestial bodies.

Constellations •

Different groups of stars form various patterns and they are called constellations. Saptarshi is an example of constellations.

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In ancient times, with the help of stars directions were determined during night time. The North Star indicates the north direction (Pole Star) and it remains in the same position in the sky.

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Celestial bodies that do not have their own heat and light and lit by the light of the stars are called planets.

Solar System

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The solar system is made up of the Sun, eight planets, satellites and other celestial bodies.

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The sun is in the centre of the solar system.

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It is huge and made up of extremely hot gases.

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It provides the pulling force that binds the solar system

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There are eight planets in our solar system.

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In order of their distance from the sun, they are:

The Sun

Planets

1. 2. 3. 4. 5. 6. 7. 8.

Mercury Venus Earth Mars Jupiter Saturn Uranus and Neptune

Inner Planets •

These planets are very close to the sun.

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They are made up of rocks.

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Inner Planets are: •

MERCURY- One orbit around sun – 88 days, One spin on axis – 59 days.

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VENUS – One orbit around sun – 255 days. One spin on axis – 243 days

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EARTH – One orbit around sun – 365 days. One spin on axis – 1 day Number of moons – 1

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MARS – One orbit around sun – 687 days One spin on axis – 1 day, number of moons – 02

Outer Planets •

Very-very far from the sun and are huge planets made up of gases and liquids •

JUPITER – One orbit around sun – 11 years, 11 months about 12 years. One spin on axis – 9 hours, 56 minutes, number of moons – 16

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SATURN – One orbit around sun – 29 years, 5 months. One spin on axis – 10 hours 40 minutes, number of moons – about 18.

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URANUS – One orbit around sun – 84 years. One spin around axis – 17 hours 14 minutes, number of moons – about 17.

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NEPTUNE – One orbit around sun – 164 years. One spin on axis-16 hours 7 minutes, number of moons – 8

Asteroids

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Asteroids are numerous tiny bodies which also move around the Sun apart from the stars, planets and satellites.

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They are found between the orbits of Mars and Jupiter.

Meteoroids •

Meteoroids are small pieces of rocks which move around the sun.

Mass movements •

Mass movement is also known as mass wasting.

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It is the movement of masses of bodies of mud, bedrock, soil, and rock debris, which commonly happen along steep-sided hills and mountains because of the gravitational pull.

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Gravity exerts its force on all matter, both bedrock and the products of weathering.

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Hence, weathering is not essential for mass movement though it helps mass movements.

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Mass movements which are sliding of huge amounts of soil and rock are seen in mudslides, landslides, and avalanches.

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The air, water or ice does not transport debris with them from place to place but on the other hand the debris may transport with it water, ice or air.

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These are very active over weathered slopes rather than over unweathered materials.

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Mass movements do not come under erosion though there is a shift of materials from one place to another.

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Heave, flow and slide are the three forms of movements.

Causes preceding Mass movements •

There are many activating causes preceding mass movements. They are : •

Removal of support from below to materials above through natural or artificial means.

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An upsurge in height of slopes and gradient.

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Overfilling through addition of materials by artificial filling or naturally.

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Overburdening due to heavy rainfall, saturation, and lubrication of slope materials.

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Elimination of material or load from over the original slope surfaces.

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Event of explosions, earthquakes, etc.

•

Extreme natural seepage.

•

Heavy drawdown of water from reservoirs, lakes, and rivers leading to a slow outflow of water from under the slopes or river banks.

•

Indiscriminate removal of natural vegetation.

Mass movements can be classified into two major classes: •

Rapid movements

•

Slow movements

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Geomorphic processes •

Geomorphological processes are natural mechanisms of erosion, weathering, and deposition that result in the alteration of the surficial materials and landforms at the surface of the earth.

•

The exogenic and endogenic forces cause chemical actions and physical pressures on earth materials

•

This brings about changes in the shape of the surface of the earth which are known as geomorphic processes.

•

Mass wasting, weathering, deposition, and erosion are exogenic geomorphic processes.

•

Volcanism and Diastrophism are endogenic geomorphic processes.

•

Any exogenic element of nature such that ice, water, and the wind that are capable of obtaining and carrying earth materials can be called a geomorphic agent.

•

When these elements of nature become portable due to gradients, they remove the materials and transport them over slopes and deposit them at a lower level.

•

The gravitational stresses are as vital as the other geomorphic processes.

•

Gravity is the force that is keeping us in contact with the surface and it is the force that switches on the movement of all surface material on earth.

•

It is the directional force stimulating all downslope movements of matter and it also causes stresses on the earth’s materials.

•

Indirect gravitational stresses stimulate tide and wave induced winds and currents.

•

Without gradients and gravity there would be no movement and therefore no transportation, erosion, and deposition are possible.

•

All the movements either on the surface of the earth or within the earth happen due to gradients —from high pressure to low pressure areas, from higher levels to lower levels, etc.

Weathering •

Weathering is the action of components of weather and climate materials over Earth.

•

There are several processes within weathering which act either independently or together to affect the materials of the earth in order to cut them to fragmental state.

•

This process causes the disintegration of rocks near the surface of the Earth.

•

It loosens and breaks down the surface minerals of rocks so they can be carried away by agents of erosion such as wind, water, and ice.

•

As very little or no motion of materials takes place in weathering, it is an in-situ or on-site process.

•

Flora and fauna life, water and atmosphere are the main reasons of weathering.

•

Weathering processes are determined by many climatic, topographic, vegetative factors and complex geological factors.

•

Climate has a significant role in weathering.

•

The weathering processes not only differ from climate to climate but also with the depth of the weathering mantle.

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•

The degree of weathering that happens depends upon the resistance to weathering of the minerals in the rock and the degree of the biological, physical, and chemical stresses.

•

The minerals in rocks that are formed under high pressure and temperature inclined to be less resistant to weathering, whereas minerals formed at low pressure and temperature are more resistant to weathering.

Three major groups of weathering processes •

There are three major groups of weathering processes: •

Biological Weathering

•

Chemical Weathering

•

Physical or Mechanical Weathering

Biological weathering is the wearying and subsequent fragmentation of rocks by animals, plants, and microbes. Physical or mechanical weathering is the weakening and consequent disintegration of rocks by physical forces. Chemical weathering is the weakening and subsequent breakdown of rocks by chemical reactions. Significance Of Weathering Weathering •

Weathering denotes the process of wearing, breaking up, and fragmentation of the rock that creates the surface of the ground and that remains exposed to the weather.

•

The process results from forces of weather like rain action, variations in temperature and frost action.

Significance of weathering to human life •

Weathering is the initial stage in the formation of soil.

•

It produces other natural resources, for instance, clay which is used for making bricks.

•

Another significance is weathering weakens rocks making them easier for people to exploit, for example, by mining and quarrying

•

This process is accountable for the fragmentation of the rocks into smaller fragments and making the way for creation of not only soils and regolith, but also mass movements and erosion.

•

Biodiversity, and Biomes are basically a result of vegetation, and forests rely upon the depth of weathering mantles.

•

Erosion cannot be significant if the rocks are not weathered.

•

It means weathering aids erosion, mass wasting and reduction of relief and modifications in landforms are a result of erosion.

•

Weathering of rocks and deposits helps in the augmentation and concentrations of some valuable ores of manganese, aluminum, iron, and copper, etc. which have a great significance in the economy of the country.

Enrichment

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•

When rocks experience weathering, particular materials are removed through chemical or physical leaching by groundwater.

•

Thereby the congregation of leftover valuable materials increases.

•

Without weathering, the concentration of the same valuable material may not be adequate and economically feasible to exploit process and refine.

•

This is as called enrichment.

Biological Weathering •

Biological weathering only refers to weathering caused by plants, animals, fungi, and microorganisms such as bacteria.

•

It is contributed to or removal of ions and minerals from the weathering environment and physical variations due to movement or development of organisms.

•

It is also the wearying and subsequent fragmentation of rock by plants, animals, and microbes.

Agents of Biological Weathering In the next section, we talk about the agents of biological weathering such as microorganisms, humans, plants and animals. Biological Weathering by Microorganisms •

Wedging and burrowing by organisms like termites, earthworms, rodents, etc. help in showing the new surfaces to chemical attack and helps in the penetration of air and moisture.

•

Bacteria, mosses, algae, and lichens frequently grow on rock surfaces, particularly in humid areas.

•

They form weak acids, which can convert some of the minerals to clay.

•

Algae growth can deteriorate several rock types and make it more exposed to weathering.

Biological Weathering by Humans •

Humans also play an important role in biological weathering.

•

Construction activities like road building, mining also causes weathering.

•

Human beings by disturbing vegetation, ploughing and cultivating soils, also help in blending and producing new contacts between water, minerals, and air in the earth materials.

Biological Weathering by Plants and Animals •

Decomposition of plant and animal help in the creation of carbonic acids, humic and other acids which boost decay and solubility of some elements.

•

Roots of plants exert tremendous pressure on the earth materials mechanically breaking them apart.

Physical Weathering Physical Weathering Processes

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•

Physical or mechanical weathering processes are influenced by some applied forces.

•

The applied forces are: •

Gravitational forces like shearing stress, load, and overburden pressure.

•

Expansion forces due to crystal growth, animal activity or temperature variations.

•

Water pressures regulated by drying and wetting cycles.

Many of these forces are applied both at the surface and within different earth materials leading to rock breakage. Most of the physical weathering processes are caused by pressure release and thermal expansion. Unloading and Expansion •

Elimination of covering rock load because of sustained erosion causes vertical pressure release with the result that the upper layers of the rock enlarge producing fragmentation of rock masses.

•

Fractures will occur roughly parallel to the ground surface.

•

In areas of curved ground surface, arched fractures incline to create massive sheets or exfoliation slabs of rock.

•

Exfoliation sheets causing from expansion due to pressure release and unloading may measure hundreds or even thousands of metres in horizontal extent.

•

Big, smooth rounded domes are called exfoliation domes.

Temperature Changes and Expansion •

Several minerals in rocks possess their own limits of contraction and expansion.

•

With an upsurge in temperature, all minerals enlarge and thrust against its neighbour and as temperature drops, a corresponding shrinkage takes place.

•

Due to diurnal changes in the temperatures, this internal movement among the mineral grains of the superficial layers of rocks takes place repeatedly.

•

This process is effective in high elevations and arid climates where diurnal temperature variations are extreme.

Freezing, Thawing and Frost Wedging •

Frost weathering happens due to development of ice within openings and cracks of rocks during recurrent cycles of melting and freezing.

•

This process is effective at high elevations in mid-latitudes where melting and freezing is frequently recurrent.

•

Glacial regions are subject to frost wedging every day.

•

In this course, the rate of freezing is significant.

•

Hasty freezing of water causes its high pressure and rapid expansion.

•

The resulting expansion affects joints, cracks and small intergranular fractures to become wider and wider till the rock breaks apart.

Salt Weathering •

Salt crystallisation is most effective of all salt-weathering processes.

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•

Salts in rocks enlarge due to hydration, crystallisation and thermal action.

•

Various salts like sodium, barium, calcium, potassium, and magnesium, have an inclination to enlarge.

•

Enlargement of these salts relies on temperature and their thermal properties.

•

High-temperature ranges between 30 and 50 degrees Celsius of surface temperatures in deserts support such salt expansion.

•

Salt crystals in the adjacent surface pores cause splitting of single grains within rocks, which ultimately drop.

•

This process of dropping of individual grains may result in granular disintegration or granular foliation.

Chemical Weathering •

A cluster of weathering processes namely solution, carbonation, hydration, oxidation, and reduction.

•

These processes act on rocks to decompose, dissolve or moderate them to a fine clastic state through chemical reactions by oxygen, surface/ soil water, and other acids.

•

Water and air along with heat must be present to speed up all chemical reactions.

•

When substances are dissolved in acids or water, then the water or acid with dissolved substances is called a solution.

•

This process includes the removal of solids in solution and depends upon the solubility of a mineral in weak acids or water.

•

Many solids disintegrate and mix up as a suspension in water as they come in contact with water.

•

Some of the soluble rock-forming minerals like sulphates, nitrates, and potassium, etc. are affected by this process.

•

Hence, these minerals are simply leached out without leaving any remains in rainy climates and accumulate in dry regions.

•

Minerals like calcium magnesium bicarbonate and calcium carbonate present in limestone are soluble in water containing carbonic acid and are transported away in water as a solution.

•

Carbon dioxide formed by decomposing organic matter along with soil water significantly assists in this reaction.

•

Sodium chloride is also a rock-forming mineral and is vulnerable to this process of solution.

•

Carbonation, oxidation and Hydration go hand in hand and accelerate the weathering process.

Solution

Carbonation •

Carbonation is the reaction of bicarbonate and carbonate with minerals.

•

It is a general process helping the fragmentation of feldspars and carbonate minerals.

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•

Carbon dioxide from the soil and atmospheric air is absorbed by water to form carbonic acid that acts like weak acid.

•

Magnesium carbonates and Calcium carbonates are dissolved in carbonic acid.

•

These are removed in a solution without leaving any residue resulting in cave formation.

•

Hydration is the chemical addition of water.

•

Minerals take up water and enlarge.

•

This enlargement causes an increase in the volume of the material itself or rock.

•

This process is long and reversible, sustained recurrence of this process causes fatigue in the rocks.

•

This may lead to their disintegration of rocks.

Hydration

Oxidation and Reduction •

In weathering, oxidation denotes a mixture of a mineral with oxygen to form hydroxides or oxides.

•

Oxidation happens where there is ready access to the oxygenated waters and atmosphere.

•

The minerals commonly involved in this process are manganese, sulphur, iron, etc.

•

In the process of oxidation, rock fragmentation happens due to the disturbance caused by adding of oxygen.

•

Red colour of iron upon oxidation turns to yellow or brown.

•

When oxidised minerals are positioned in a situation where oxygen is absent, reduction occurs.

•

Such circumstances exist commonly below the water table, waterlogged ground and in areas of stagnant water.

•

Red colour of iron upon reduction turns to greenish or bluish grey.

•

These weathering processes are interconnected.

Exogenic processes •

The exogenic processes obtain their energy from the gradients generated by tectonic factors, processes, their corresponding driving forces and atmosphere determined by the energy from the sun.

•

Precipitation and temperature are the two significant climatic components that regulate different processes.

•

Whole exogenic geomorphic processes are covered under a common term, denudation which means to uncover.

•

Weathering, transportation, and erosion are comprised in denudation.

•

Gravitational force acts upon every material on earth having a sloping surface and incline to create the movement of matter in downward slope direction.

Stress

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•

Force applied per unit area is called stress.

•

Stress is created in a solid by pulling or pushing and this induces deformation.

•

Forces acting along the surfaces of earth materials are shear stresses and it breaks rocks and other earth materials.

•

The shear stresses result in slippage or angular displacement.

•

Besides gravitational stress, earth materials become exposed to molecular stresses that may be caused by several factors amongst which crystallisation, melting, and temperature variations are the most usual.

•

Chemical processes generally lead to loosening of bonds between grains, dissolving of soluble minerals or strengthening materials.

•

Therefore, the fundamental cause that leads to erosion, mass movements, and weathering is the development of stresses in the body of the earth materials.

•

The effects of most of the exogenic geomorphic processes are minor and slow.

•

It may be imperceptible in a short time span, but will in the long run influence the rocks harshly due to constant fatigue.

Endogenic Process •

The energy originating from within the earth is the main force behind endogenic geomorphic processes.

•

This energy is mostly produced by rotational and tidal friction, radioactivity, and primordial heat from the origin of the earth.

•

This energy due to geothermal gradients and heat flow from within induces diastrophism and volcanism in the lithosphere.

•

Due to differences in geothermal gradients and heat flow from within, strength and crustal thickness, the action of endogenic forces are uneven.

•

Therefore the tectonically regulated original crustal surface is not uniform.

Diastrophism •

All processes that move, lift or build up portions of the crust of Earth come under diastrophism.

•

They include: •

•

Orogenic Processes: •

It includes mountain building through severe folding and faulting affecting long and narrow belts of the crust of Earth.

•

Orogeny is a mountain building process.

Epeirogenic processes: •

It involves the uplift or warping of large parts of the crust of the earth.

•

Epeirogeny is a continental building process.

•

Earthquakes comprising local, comparatively minor movements.

•

Plate tectonics comprising horizontal movements of crustal plates.

Through the processes of epeirogeny, orogeny, earthquakes and plate tectonics, there can be fracturing and faulting of the crust.

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Each of these courses causes pressure, volume and temperature (PVT) changes which in turn induce metamorphism of rocks. Volcanism •

Volcanism comprises the movement of magma onto or toward the surface of the earth and also the creation of several extrusive and intrusive volcanic forms.

Factors Controlling Temperature Distribution The temperature of air at every place is influenced by : •

The latitude of the place

•

The altitude of the place

•

Distance from the sea

•

The air- mass circulation

•

The presence of warm and cold ocean currents

•

Local aspects

The latitude •

The temperature of a place is determined by the insolation received.

•

The insolation differs according to the latitude, therefore, the temperature also differs consequently.

The altitude •

The atmosphere is indirectly heated by terrestrial radiation.

•

Therefore, the places adjacent to the sea-level record higher temperatures than the places located at higher elevations.

•

The temperature usually decreases with increasing height.

•

The rate of decrease of temperature with height is called as the normal lapse rate.

Distance from the sea •

The main factor that influences the temperature is the position of a place with respect to the sea.

•

The sea gets heated slowly and loses heat slowly compared to land.

•

Land heats up and cools down rapidly.

•

So, the difference in temperature over the sea is less compared to the terrestrial surface.

•

The places located near the sea come under the moderating influence of the sea and land breezes which regulate the temperature.

Air-mass and Ocean currents •

The passage of air masses also affects the temperature like the land and sea breezes.

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•

The places which come under the effect of warm air-masses experience higher temperature and the places that come under the influence of cold air- masses experience lower temperature.

•

Likewise, the places situated on the coast where the warm ocean currents flow record higher temperature than the places situated on the coast where the cold currents flow.

Composition and Structure of the Earth’s Atmosphere What is atmosphere? We all know that earth is a unique planet due to the presence of life. The air is one among the necessary conditions for the existence of life on this planet. The air is a mixture of several gases and it encompasses the earth from all sides. The air surrounding the earth is called the atmosphere. • •

Atmosphere is the air surrounding the earth. The atmosphere is a mixture of different gases. It contains life-giving gases like Oxygen for humans and animals and carbon dioxide for plants. It envelops the earth all round and is held in place by the gravity of the earth. It helps in stopping the ultraviolet rays harmful to the life and maintains the suitable temperature necessary for life. Generally, atmosphere extends up to about 1600 km from the earth’s surface. However, 99 % of the total mass of the atmosphere is confined to the height of 32 km from the earth’s surface.

• • •

Composition of the atmosphere • •

The atmosphere is made up of different gases, water vapour and dust particles. The composition of the atmosphere is not static and it changes according to the time and place.

Gases of the atmosphere • •

The atmosphere is a mixture of different types of gases. Nitrogen and oxygen are the two main gases in the atmosphere and 99 percentage of the atmosphere is made up of these two gases. Other gases like argon, carbon dioxide, neon, helium, hydrogen, etc. form the remaining part of the atmosphere. The portion of the gases changes in the higher layers of the atmosphere in such a way that oxygen will be almost negligible quantity at the heights of 120 km. Similarly, carbon dioxide (and water vapour) is found only up to 90 km from the surface of the earth.

• • •

Nitrogen •

The atmosphere is composed of 78% nitrogen.

•

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•

Biotic things need nitrogen to make proteins.

•

The Nitrogen Cycle is the way of supplying required nitrogen for living things.

•

The atmosphere is composed of 21% oxygen.

•

It is used by all living things and is essential for respiration.

•

It is obligatory for burning.

•

The atmosphere is composed of 0.9% argon.

•

They are mainly used in light bulbs.

Oxygen

Argon

Carbon Dioxide •

The atmosphere is composed of 0.03% carbon dioxide.

•

Plants use it to make oxygen.

•

It is significant as it is opaque to outgoing terrestrial radiation and transparent to incoming solar radiation.

•

It is also blameable for the greenhouse effect.

OZONE GAS: • • •

Ozone is another important component of the atmosphere found mainly between 10 and 50 km above the earth’s surface. It acts as a filter and absorbs the ultra-violet rays radiating from the sun and prevents them from reaching the surface of the earth. The amount of ozone gas in the atmosphere is very little and is limited to the ozone layer found in the stratosphere.

Water Vapour • • • • •

•

•

Gases form of water present in the atmosphere is called water vapour. It is the source of all kinds of precipitation. The amount of water vapour decreases with altitude. It also decreases from the equator (or from the low latitudes) towards the poles (or towards the high latitudes). Its maximum amount in the atmosphere could be up to 4% which is found in the warm and wet regions. Water vapour reaches in the atmosphere through evaporation and transpiration. Evaporation takes place in the oceans, seas, rivers, ponds and lakes while transpiration takes place from the plants, trees and living beings. Water vapour absorbs part of the incoming solar radiation (insolation) from the sun and preserves the earth’s radiated heat. It thus acts like a blanket allowing the earth neither to become too cold nor too hot. Water vapour also contributes to the stability and instability in the air.

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Dust Particles • • • •

Dust particles are generally found in the lower layers of the atmosphere. These particles are found in the form of sand, smoke-soot, oceanic salt, ash, pollen, etc. Higher concentration of dust particles is found in subtropical and temperate regions due to dry winds in comparison to equatorial and polar regions. These dust particles help in the condensation of water vapour. During the condensation, water vapour gets condensed in the form of droplets around these dust particles and thus clouds are formed.

Structure of the atmosphere The atmosphere can be divided into five layers according to the diversity of temperature and density. They are: 1. 2. 3. 4. 5.

Troposphere Stratosphere Mesosphere Thermosphere (Ionosphere) Exosphere

Troposphere • • • • • • •

• •

It is the lowermost layer of the atmosphere. The height of this layer is about 18 km on the equator and 8 km on the poles. The thickness of the troposphere is greatest at the equator because heat us transported to great heights by strong convectional currents. Troposphere contains dust particles and water vapour. This is the most important layer of the atmosphere because all kinds of weather changes take place only in this layer. The air never remains static in this layer. Therefore this layer is called ‘changing sphere’ or troposphere. The environmental temperature decreases with increasing height of the atmosphere. It decreases at the rate of 1 degree Celsius for every 165 m of height. This is called Normal Lapse Rate. The zone separating troposphere from the stratosphere is known as tropopause. The air temperature at the tropopause is about – 80 degree Celsius over the equator and about – 45 degree Celsius over the poles. The temperature here is nearly constant, and hence, it is called tropopause.

Stratosphere • • •

Stratosphere is found just above the troposphere. It extends up to a height of 50 km. The temperature remains almost the same in the lower part of this layer up to the height of 20 km. After this, the temperature increases slowly with the increase in the height. The temperature increases due to the presence of ozone gas in the upper part of this layer.

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•

Weather related incidents do not take place in this layer. The air blows horizontally here. Therefore this layer is considered ideal for flying of aircraft. The upper limit of the stratosphere is known as stratopause. One important feature of stratosphere is that it contains a layer of ozone gas. The relative thickness of the ozone layer is measured in Dobson Units. It is mainly found in the lower portion of the stratosphere, from approximately 20 to 30 km above the earth’s surface. It contains a high concentration of ozone (O3) in relation to other parts of the atmosphere. It is the region of the stratosphere that absorbs most of the sun’s ultra-violet radiations.

• • • • • •

Mesosphere • • •

It is the third layer of the atmosphere spreading over the stratosphere. It extends up to a height of 80 km. In this layer, the temperature starts decreasing with increasing altitude and reaches up to – 100 degree Celsius at the height of 80 km. Meteors or falling stars occur in this layer. The upper limit of the mesosphere is known as mesopause.

• •

Thermosphere • •

This layer is located between 80 and 400 km above the mesopause. It contains electrically charged particles known as ions, and hence, it is known as the ionosphere. Radio waves transmitted from the earth are reflected back to the earth by this layer and due to this, radio broadcasting has become possible. The temperature here starts increasing with heights.

• •

Exosphere • •

The exosphere is the uppermost layer of the atmosphere. Gases are very sparse in this sphere due to the lack of gravitational force. Therefore, the density of air is very less here.

General circulation of the Atmosphere •

The pattern of the movement of the planetary winds is called general circulation of the atmosphere.

Factors for General Circulation of the Atmosphere •

The pattern of planetary winds largely depends on: •

Latitudinal variation of atmospheric heating

•

The emergence of pressure belts

•

The migration of belts following the apparent path of the sun

•

The distribution of continents and oceans

•

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The general circulation of the atmosphere also sets in motion the marine water circulation which affects the climate of the Earth. The air at the ITCZ (Inter Tropical Convergence Zone) upsurges because of convection caused by high insolation and low pressure is generated. The winds from the tropics join at this low-pressure zone. The joined air upsurges along with the convective cell. It reaches the top of the troposphere up to an altitude of 14 km. It further moves toward the poles. This causes accumulation of air at about 30 o North and South. Another reason for sinking is the cooling of air when it reaches 30 degrees North and South latitudes. Downward near the land surface, the air flows towards the equator as the easterlies. The easterlies from either side of the equator converge in the Inter-Tropical Convergence Zone (ITCZ). Such circulations from the surface up and vice-versa are called cells. This type of a cell in the tropics is called Hadley Cell. In the mid-latitudes, the circulation is that of dipping cold air that comes from the poles and the mounting warm air that blows from the subtropical high. At the surface, these winds are called westerlies and the cell is known as the Ferrel cell. At polar latitudes, the cold dense air subsides near the poles and blows towards middle latitudes as the polar easterlies. This cell is called the polar cell. These Ferrel cells, Hadley Cell, and polar cell set the configuration for the general circulation of the atmosphere. General Atmospheric Circulation and its Effects on Oceans •

The general circulation of the atmosphere also influences the oceans.

•

Warming and cooling of the Pacific Ocean is most significant in terms of general atmospheric circulation.

•

The warm water of the central Pacific Ocean gradually drifts towards the South American coast and substitutes the cool Peruvian current.

•

Such presence of warm water off the coast of Peru is known as the El Nino.

•

The El Nino is associated with the pressure variations in Australia and Central Pacific.

•

This variation in pressure condition over the Pacific is known as the southern oscillation.

•

The combined phenomenon of El Nino and southern oscillation is known as ENSO.

Heating and Cooling of atmosphere •

There are various ways of heating and cooling of the atmosphere.

•

The earth after being warmed by insolation transfers the heat to the atmospheric layers in long waveform

Conduction •

The air in interaction with the land gets heated gradually and the upper layers in touch with the lower layers also get heated. This process is called conduction.

•

This process takes place when two bodies of uneven temperature are in contact with one another, there is a flow of energy from the warmer to the cooler body.

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•

The heat transfer continues until both the bodies reach the same temperature or the contact is interrupted.

•

This process is significant in heating the lower layers of the atmosphere.

Convection •

The air in contact with the earth upsurges vertically on heating in the form of currents and transfers the heat of the atmosphere.

•

This vertical heating of the atmosphere is known as convection.

•

The convective transfer of energy is limited only to the troposphere.

•

The transfer of heat through horizontal movement of air is called advection.

•

Horizontal movement of the air is comparatively more significant than the vertical movement.

•

Most of the diurnal variation in weather is caused by advection only in the middle latitudes.

•

During summer in tropical regions predominantly in Northern India, local winds called ‘loo’ is the result of advection process.

Advection

Atmospheric Pressure •

The weight of a column of air contained in a unit area from the mean sea level to the top of the atmosphere is called the atmospheric pressure.

•

It is measured in force per unit area.

•

It is expressed in ‘milibar’ or mb unit.

•

In application level, the atmospheric pressure is stated in kilo-pascals.

•

It is measured by the aneroid barometer or mercury barometer.

•

In lower atmosphere, pressure declines rapidly with height.

•

The vertical pressure gradient force is much larger than that of the horizontal pressure gradient and is commonly balanced by an almost equal but opposite gravitational force.

•

Low-pressure system is encircled by one or more isobars with the lowest pressure at centre.

•

High pressure system is also encircled by one or more isobars with highest pressure in centre.

•

Isobars are lines connecting places having equal pressure.

Pressure Gradient •

The rate of change of pressure in regard to distance is the pressure gradient.

Pressure belts •

There is a pattern of alternate high and low-pressure belts over the earth.

•

There are seven pressure belts.

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•

Except the Equatorial low, there are two Sub-Tropical highs (in North and South), the two Sub-polar lows (in North and South), and the two Polar highs (in North and South).

•

The above-given pressure belts oscillate with the movement of the sun.

•

In the northern hemisphere, they move southwards in winter, and in summers they move northwards.

•

The Equatorial region gets abundant heat and warm air being light, the air at the Equator rises, generating a low pressure.

•

Equatorial low •

It is found near the equator.

•

The sea level pressure is low.

•

The region in 30 degrees North and 30 degrees South, which are high-pressure areas.

•

The region in 60 degrees North and 60 degrees South, which are low-pressure belts.

•

These occur near poles which have high pressure.

Subtropical high

Sub-polar Lows

Polar Highs

Tropical Cyclones

•

Tropical cyclones are regarded as one of the most devastating natural calamities in the world.

•

They originate and intensify over warm tropical oceans.

•

These are ferocious storms that originate over oceans in tropical areas and move over to the coastal areas causing violent winds, very heavy rainfall, and storm outpourings.

Names of cyclone in different regions They are known as: •

Cyclones in the Indian Ocean

•

Hurricanes in the Atlantic

•

Typhoons in the Western Pacific and the South China Sea

•

Willy-willies in Western Australia

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Conditions for the formation of Tropical Cyclone The conditions which favour the formation and intensification of tropical cyclone storms are: •

Large sea surface with a temperature higher than 27° C

•

Presence of the Coriolis force

•

Small differences in the vertical wind speed

•

A pre-existing weak- low-pressure area or low-level-cyclonic circulation

•

Upper divergence above the sea level system

Formation of Cyclone •

The energy that strengthens the storm comes from the condensation process in the towering cumulonimbus clouds, surrounding the centre of the storm.

•

With an uninterrupted supply of moisture from the sea, the storm is again strengthened.

•

On reaching the terrestrial region the moisture supply is cut off and the storm dissipates.

•

The place where a tropical cyclone cuts the coast is called the landfall of the cyclone.

•

A landfall is frequently accompanied by sturdy winds, heavy rain and mounting sea waves that could threaten people and cause damage to properties.

•

Cyclones which cross 20 degrees North latitude are more destructive.

•

They cover a larger area and can originate over the land and sea whereas the tropical cyclones originate only over the seas and on reaching the land they dissipate.

Eye of Cyclone •

A mature tropical cyclone is characterised by the strong spirally circulating wind around the centre which is called the eye.

•

The eye is an area with calm weather descending air.

•

It is characterized by light winds and clear skies.

•

Around the eye is the eyewall, where there is a strong spiralling rise of air to a greater height reaching the tropopause.

•

The wind reaches maximum velocity in this region and torrential rain occurs here.

•

From the eyewall, rain bands may radiate and trains of cumulus and cumulonimbus clouds may drift into the outer region.

Eye Wall

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The Rock Cycle

•

The rock cycle is a basic concept in geology that defines the laborious transitions through geologic time among the three main rock types: •

Igneous rocks

•

Sedimentary rocks

•

Metamorphic rocks

Rocks do not remain in their original form for a long period as they undergo a transformation. This cycle is an uninterrupted process through which old rocks are converted into new ones. Igneous rocks are primary rocks. These rocks can be changed into metamorphic rocks. Sedimentary and metamorphic rocks form from these primary rocks. The fragments evolved out of metamorphic rocks and igneous again form into sedimentary rocks. Sedimentary rocks themselves can develop into fragments. The crustal rocks -igneous, metamorphic and sedimentary-once formed may be carried down into the interior of the earth through subduction. In this process, parts or entire crustal plates subduct under another plate and the same melt at high temperature in the interior. This results in the formation of molten magma, the unique source for igneous rocks. The Processes of the Rock Cycle •

The rock cycle encompasses several processes.

•

The key processes of the rock cycle are: •

Crystallization

•

Erosion and sedimentation

•

Metamorphism

Forces that drive the rock cycle •

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•

Spreading ridges

•

Subduction zones

•

Continental collision

•

Accelerated erosion

•

Water

Forces Affecting the Velocity and Direction of Wind •

The air in motion is called wind.

•

The wind blows from high pressure to low pressure.

•

The wind at the surface experiences friction.

•

The rotation of the earth also affects the wind movement.

•

The force exerted by the rotation of the earth is known as the Coriolis force.

•

Therefore, the horizontal winds near the Earth’s surface respond to the combined effect of three forces: •

The Pressure Gradient Force

•

The Frictional Force

•

The Coriolis Force

Pressure Gradient Force •

The differences in atmospheric pressure generate a force.

•

The rate of change of pressure with regard to distance is known as the pressure gradient.

•

The pressure gradient is weak where the isobars are distant and strong where the isobars are close by to each other.

Frictional Force •

It impacts the speed of the wind.

•

The friction is maximum at the surface and minimal over the sea surface.

•

The influence of frictional force usually stretches up to an elevation of 1 – 3 km.

Coriolis force •

The rotation of the earth about its axis affects the direction of the wind and this force is called the Coriolis force.

•

It is directly proportional to the angle of latitude.

•

It deflects the wind to the left direction in the southern hemisphere and the right direction in the northern hemisphere.

•

The deflection is more when the wind velocity is high.

•

It is maximum at the poles and is absent at the equator.

•

The force acts perpendicular to the pressure gradient force.

•

The pressure gradient force is perpendicular to an isobar.

•

The higher the pressure gradient force, the more is the speed of the wind and the larger is the deflection in the direction of wind happens. 50

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•

As a result of these two forces functioning perpendicular to each other, in the lowpressure areas the wind blows around it.

•

The Coriolis force is zero at the equator and the wind blows perpendicular to the isobars.

The Nitrogen Cycle •

The nitrogen cycle is the biogeochemical cycle.

•

Nitrogen is a main constituent of the atmosphere encompassing about 75% of the atmospheric gases.

•

It is also a vital constituent of different organic compounds such as the vitamins, nucleic acids, pigments, amino acids, and proteins.

•

The major source of free nitrogen is the action of soil micro-organisms and associated plant roots on atmospheric nitrogen found in pore spaces of the soil.

Fixation •

Fixation is the primary step in the process of converting nitrogen, usable by plants.

•

Normally, bacteria change nitrogen into ammonium.

Nitrification •

This is the process by which ammonium converted into nitrates by bacteria.

•

The plants absorb these Nitrates.

Assimilation •

Through assimilation only plants get nitrogen.

•

They absorb nitrates from the soil into their roots.

•

Then nitrogen gets used in chlorophyll, nucleic acids, and amino acids.

Ammonification •

This is part of the decaying process.

•

When a plant or animal expires, decomposers such that bacteria and fungi turn the nitrogen back into ammonium so it can go back into the nitrogen cycle.

De-nitrification •

Surplus nitrogen in the soil gets put back out into the air.

•

There are special bacteria that execute this job as well.

The Oxygen Cycle •

The oxygen cycle is the biogeochemical cycle of oxygen.

•

The cycling of oxygen is a highly complex process.

•

Oxygen occurs in several combinations and chemical forms.

•

It combines with nitrogen to form nitrates.

•

It also combines with several other elements and minerals to form different oxides such as the iron oxide, aluminium oxide and others.

•

The carbon dioxide is absorbed by plants during photosynthesis.

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•

A considerable amount of oxygen is produced from the decomposition of water molecules by sunlight during photosynthesis.

•

Respiration by humans and animal consumes oxygen and releases carbon dioxide into the atmosphere.

•

Again this carbon dioxide is again, taken up by plants, for photosynthesis and the process repeat.

The Carbon Cycle •

The carbon cycle is chiefly the conversion of carbon dioxide.

•

It is the biogeochemical cycle by which carbon is interchanged among the biosphere, hydrosphere, atmosphere, and geosphere of the Earth.

•

Plants use carbon dioxide and sunlight to make their own food and grow.

•

The conversion of carbon dioxide is started by the fixation of carbon dioxide through photosynthesis from the atmosphere.

•

Such conversion results in the creation of carbohydrate, glucose that may be transformed to other organic compounds like starch, sucrose, cellulose, etc.

•

In this process, more carbon dioxide is generated and discharged through its roots or leaves during the day.

•

The leftover carbohydrates become part of the plant tissue.

•

Plant tissues are eaten by the herbivorous animals.

•

The carbon becomes part of the plant.

•

Plants that perish and are buried will turn into fossil fuels made of carbon like coal and oil over millions of years.

•

Most of the carbon quickly enters the atmosphere as carbon dioxide while burning the fossil fuels.

•

Carbon dioxide is a greenhouse gas and traps heat in the atmosphere.

•

Earth would be a frozen world without Carbon dioxide and other greenhouse gases.

Biogeochemical Cycles •

Biological Chemical + Geological Process= Biogeochemical

•

Energy flows through an ecosystem and is released as heat, but chemical elements are recycled.

•

The ways in which an element or compound moves between its several biotic and abiotic forms and locations in the biosphere is called a biogeochemical cycle.

•

It is a movement of nutrients and other elements between living and non-living beings.

•

The sun is the basic source of energy on which all life depends.

•

Life on earth comprises a great variety of living organisms.

•

These living organisms exist and survive in a diversity of associations. Such survival encompasses the presence of systemic flows such as flows of energy, water, and nutrients.

•

The balance of the chemical elements is maintained by a cyclic movement through the tissues of plants and animals.

•

The cycle starts by absorbing the chemical elements by the organism and is returned to the air, water, and soil through decomposition. 52

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These cycles are largely energized by solar insolation.

•

There are two types of biogeochemical cycles: •

The gaseous cycle •

•

In the gaseous cycle, the main reservoir of nutrients is the atmosphere and the ocean.

The sedimentary cycle •

In the sedimentary cycle, the main reservoir is the soil and the sedimentary and other rocks of the earth’s crust.

Important Biogeochemical Cycles •

The Carbon Cycle

•

The Nitrogen Cycle

•

The Oxygen Cycle

•

The Phosphorus Cycle

•

The Sulphur Cycle

•

The Water Cycle/ Hydrological Cycle

•

The Rock Cycle

Salinity Of Ocean Water •

Salinity means the total content of dissolved salts in Sea or Ocean.

•

Salinity is calculated as the amount of salt dissolved in 1,000 gm of seawater.

•

It is generally expressed as ‘parts per thousand’ (ppt).

•

A salinity of 24.7 % has been regarded as the upper limit to fix ‘brackish water’.

•

It is a significant factor in deciding several characteristics of the chemistry of natural waters and of biological processes.

Factors affecting ocean salinity •

Salinity, temperature, and density of water are interconnected. The salinity of water in the surface layer of oceans is influenced by: •

Evaporation

•

Precipitation

In the coastal regions, the surface salinity is influenced by the freshwater flow from rivers. In the Polar region, the surface salinity is influenced by the processes of freezing and melting of ice. The wind also influences the salinity of an area by moving water to other areas. The ocean currents contribute to the salinity variations. The change in the density or temperature influences the salinity of water in an area. Highest salinity in water bodies Lake Van in Turkey

330 o/oo

Dead Sea

238 o/oo

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Great Salt Lake

220 o/oo

Dissolved Salts in Sea Water (gm of Salt per kg of Water) Chlorine

18.97

Sodium

10.47

Sulphate

2.65

Magnesium

1.28

Calcium

0.41

Potassium

0.38

Bicarbonate

0.14

Bromine

0.06

Borate

0.02

Strontium

0.01

Share of different salts •

Sodium chloride — 77.7%

•

Magnesium chloride—10.9%

•

Magnesium sulphate —.4.7%

•

Calcium sulphate — 3.6%

•

Potassium sulphate — 2.5%

Horizontal And Vertical Distribution Of Salinity •

The salinity for normal Open Ocean ranges between 33o/oo and 37 o/oo.

•

The highest salinity is recorded between 15° and 20° latitudes.

•

Maximum salinity (37 o/oo) is observed between 20° N and 30° N and 20° W – 60° W.

•

The salinity gradually decreases towards the north.

•

The salinity sometimes reaches up to 70 o/oo in the hot and dry regions where evaporation is high.

•

The salinity variation in the Pacific Ocean is largely due to its shape and larger areal stretch.

•

In the landlocked Red Sea, the salinity is 41o/oo which considerably high.

•

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Due to the influx of melted water from the Arctic region, the salinity decreases from 35 o/oo – 31 o/oo on the western parts of the northern hemisphere.

•

The North Sea records higher salinity due to more saline water brought by the North Atlantic Drift despite its location in higher latitudes.

•

Due to the influx of river waters in the large amount, the Baltic Sea records low salinity.

•

The Mediterranean Sea accounts for the higher salinity due to high evaporation.

•

Salinity is very low in the Black Sea due to massive freshwater influx by rivers.

•

The average salinity of the Indian Ocean is 35 o/oo.

•

The low salinity trend in the Bay of Bengal is due to the influx of river water.

•

But the Arabian Sea displays higher salinity due to the low influx of fresh water and high evaporation.

Vertical Distribution of Salinity •

Salinity changes with depth, but the way it changes relies on the position of the sea.

•

Salinity at the surface of the sea is decreased by the input of fresh waters or increased by the loss of water to ice or evaporation.

•

Salinity at depth is fixed as neither water nor salt can be added in it.

•

There is a marked difference in the salinity between the surface zones and the deep zones of the oceans.

•

The lower saline water remains above the higher saline dense water.

•

Salinity, usually, increases with depth and there is a distinct zone called the halocline, where salinity increases abruptly.

•

The increasing salinity of seawater causes an increase in the density of water.

•

High salinity seawater, usually, sinks below the lower salinity water. This leads to stratification by salinity.

Koeppen’s Climate Classification •

Koeppen’s Classification of climate is the most commonly used classification of climate.

•

This climate classification scheme was developed by Wladimir Peter Koeppen in 1884.

•

He recognized a close relationship between the distribution of vegetation and climate.

•

The categories are based on the data of annual and monthly averages of temperature and precipitation.

•

He selected specific values of temperature and precipitation and related them to the distribution of vegetation and used these values for classifying the climates.

•

The Koeppen climate classification system recognizes five major climatic types and each type is designated by a capital letter- A, B, C, D, E, and H.

•

The seasons of dryness are indicated by the small letters: f, m, w, and s. •

f -no dry season

•

m – Monsoon climate

•

w- Winter dry season

•

s – Summer dry season

The small letters a, b, c, and d refer to the degree of severity of temperature.

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List of climatic groups and their characteristics according to Koeppen Group

Characteristics

A-

Tropical

Average temperature of the coldest month is 18° C or higher

B-

Dry Climates

Potential evaporation exceeds precipitation

C-

Warm Temperate

The average temperature of the coldest month of the (Mid-latitude) climates years is higher than minus 3°C but below 18°C

D- Cold Snow forest

The average temperature of the coldest month is minus 3° C or below

E-

Cold Climates Average temperature for all months is below 10° C

Cold Climates

H- Highlands

Cold due to elevation

Climatic Types According to Koeppen Group

Type

Letter Code

Characteristics

A-Tropical Humid Climate

Tropical Wet

Af

No dry season

Tropical Monsoon

Am

Monsoonal, Short dry season

Tropical wet and dry

Aw

Winter dry season

Subtropical Steppe

BSh

Low-latitude semi-arid or dry

Subtropical Desert

BWh

Low-latitude arid or dry

Mid-latitude Steppe

BSk

Mid-latitude semi-arid or dry

Mid-latitude Desert

BWk

Mid-latitude arid or dry

Humid subtropical

Cfa

No dry season

Mediterranean

Cs

Dry hot summer

Marine west coast

Cfb

No dry season, warm and cool summer

D- Cold Snowforest Climates

Humid Continental Subarctic

Df

No dry season, severe winter

Dw

Winter dry and very severe

E-Cold climates

Tundra

ET

No true summer

Polar ice cap

EF

Perennial ice

B-Dry Climate

C-Warm temperate Climates

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H-highland

Highland

H

Highland with snow cover

Climate Change What is climate? •

Climate is the average weather in a place over many years.

•

The weather can change in just a few hours whereas climate takes millions of years to change.

•

Planet earth has witnessed many variations in climate since the beginning.

What are the pieces of evidence of Climate Change? •

Sea level rise

•

Global temperature rise

•

Warming oceans

•

Shrinking ice sheets

•

Declining Arctic sea ice

•

Glacial retreat

•

Extreme natural events

•

Ocean acidification

•

Decreased snow cover

Causes of Climate Change •

There are several causes of climate change. The most significant anthropogenic effect on the climate is the increasing trend in the concentration of greenhouse gases in the atmosphere.

The causes can be grouped into two: •

Astronomical causes

•

Terrestrial causes

•

Volcanism

•

Concentration of greenhouse

Astronomical causes •

The astronomical causes are the variations in solar output related to sunspot activities.

•

Sunspots are dark and cooler patches on the sun which rise and fall in a recurring manner.

•

When the number of sunspots increases, cooler and wetter weather and greater storminess occur.

•

These modify the amount of insolation received from the sun, which in turn, might have a bearing on the climate.

Volcanism

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•

Volcanism is regarded as another cause for climate change.

•

Volcanic eruptions throw up loads of aerosols into the atmosphere.

•

These aerosols persist in the atmosphere for a substantial period of time decreasing the radiation of sun reaching the surface of Earth.

Concentration of greenhouse gases •

The primary Greenhouse gases of concern are Chlorofluorocarbons (CFCs), Methane (CH4), Nitrous oxide (N2O), Carbon dioxide (CO2), and Ozone (O3).

•

Some other gases such as nitric oxide (NO) and carbon monoxide (CO) easily react with Greenhouse gases and affect their concentration in the atmosphere.

•

The largest concentration of Greenhouse gas in the atmosphere is carbon dioxide.

Greenhouse effect •

The greenhouse effect is a normal process that warms the surface of the Earth.

•

Solar radiation reaches the atmosphere of Earth and some of this is reflected back into space.

•

The rest of the energy of the sun is absorbed by the terrestrial and the oceans, heating the Earth.

•

Heat radiates from Earth towards space.

•

Some of this heat is trapped by greenhouse gases in the atmosphere, keeping the Earth warm enough to sustain life.

•

Human activities such as burning fossil fuels, agriculture, and land clearing are increasing the amount of greenhouse gases released into the atmosphere.

•

This is trapping extra heat, and causing the temperature of the earth to rise and ultimately result in Global Warming.

Global Warming •

Global warming is the gradual heating of the surface of the Earth, ocean, and atmosphere.

•

Global warming begins with the greenhouse effect, which is caused by the interaction between incoming radiation from the sun and the atmosphere of Earth.

•

The atmosphere is acting as a greenhouse due to the presence of greenhouse gases.

The Hydrologic Cycle Water Cycle Explanation •

Water is a cyclic resource as it is used and re-used.

•

About 71% of the planetary water is found in the oceans.

•

The remaining is held as freshwater in glaciers and ice caps, groundwater sources, lakes, soil moisture, atmosphere, streams and within life.

•

About 59% of the water on the land surface evaporates and returns back to the atmosphere.

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•

The remaining run-off on the surface penetrates into the ground or a part of it becomes glaciers.

Distribution of water on the surface of the earth Reservoir

Percentage of the total

Volume in Million Cubic km

Oceans

97.25

1,370

Ice caps and glaciers

2.05

29

Groundwater

0.68

9.5

Lakes

0.01

0.125

Soil moisture

0.005

0.065

Atmosphere

0.001

0.013

Streams and Rivers

0.0001

0.0017

Biosphere

0.00004

0.0006

Hydrological Cycle Diagram •

The hydrological cycle is the circulation of water within the hydrosphere of Earth in different forms such as liquid, solid and gaseous states.

•

It also denotes the uninterrupted exchange of water between the land surface, oceans and subsurface and the organisms.

•

The hydrologic cycle begins with the evaporation of water from the surface of the ocean.

Components and Processes of the Water Cycle Components

Processes

Water storage in oceans

Evaporation Transpiration Sublimation

Water in the atmosphere

Condensation Precipitation

Water storage in ice and snow

Snowmelt runoff to streams

Surface runoff

Streamflow freshwater storage infiltration

Groundwater storage

Groundwater discharge springs

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Evaporation •

The conversion of water from liquid to gas stage as it moves from the ground or bodies of water into the atmosphere.

•

The source of energy for evaporation is mainly solar radiation.

Transpiration •

Water vapour is also discharged from plant leaves by a process called transpiration.

Sublimation •

The process in which solid water such as snow or ice directly changes into water vapour.

Condensation •

The transformation of water vapour to liquid water droplets in the air, forming fog and clouds.

Precipitation •

The condensed water vapour falling to the surface of the Earth is known as Precipitation.

•

It occurs in the form of rain, snow, and hail.

•

Runoff is a visible flow of water in rivers, creeks, and lakes as the water stored in the basin drains out.

•

The runoff created by melting snow.

Runoff

Snowmelt

Percolation •

Water flows vertically through the soil and rocks under the effect of gravity.

Ocean Waves •

Waves are formed by energy passing through water, resulting it to move in a circular motion.

•

Water particles travel only in a small circle as a wave passes.

•

The Wind provides energy to the waves.

•

The Wind causes waves to travel in the ocean and the energy is released on coastlines.

•

The movement of the surface water rarely affects the stagnant deep bottom water of the oceans.

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•

As a wave approaches the coastline, it slows down. This is due to the friction happening between the moving water and the sea floor.

•

When the depth of water is less than half the wavelength of the wave, the wave breaks.

•

The largest waves are found in the open oceans.

•

Waves continue to grow larger as they move and absorb energy from the wind.

•

The size and shape of the waves reveal its origin.

•

Steep waves are young ones and are perhaps created by local wind.

•

Slow and steady waves originate from faraway places, probably from another hemisphere.

Clouds What is a cloud? • • • •

• •

A cloud is an accumulation or grouping of tiny water droplets and ice crystals that are suspended in the earth atmosphere. They are masses that consist of huge density and volume and hence it is visible to naked eyes. There are different types of Clouds. They differ each other in size, shape, or colour. They play different roles in the climate system like being the bright objects in the visible part of the solar spectrum, they efficiently reflect light to space and thereby helps in the cooling of the planet. Clouds are formed when the air becomes saturated or filled, with water vapour. The warm air holds more water vapour than cold air. Being made of the moist air and it becomes cloudy when the moist air is slightly cooled, with further cooling the water vapour and ice crystals of these clouds grew bigger and fall to earth as precipitation such as rain, drizzle, snowfall, sleet, or hail.

What are the different types of cloud? Clouds are classified primarily based on – their shape and their altitude. Based on shape, clouds are classified into three. They are: 1. Cirrus 2. Cumulus 3. Stratus 2. Classification of clouds – based on their altitude (height): Based on the height or altitude the clouds are classified into three. They are – 1. High Clouds 2. Middle Clouds 3. Low Clouds Note: You should also note about the another type of clouds here – ie. Clouds with great vertical extent.

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1) High Clouds • • • •

They can reach above 6000 metres or 20,000 feet. They are also known as Cirrus Clouds. They are usually thin and are made up of ice. They often indicate fair weather and hence do not produce rain.

2) Middle Clouds • • • •

They form between 6,500 feet and cirrus level or from 2000 to 6000 metres. They are also known as “Alto” clouds. They frequently indicate an approaching storm. They may sometimes produce Virga, which is a rain or snow that does not reach the ground.

3) Low Clouds • • •

They lie below 6,500 feet, which means from the surface to 2,000 meters. Low clouds are also known as Stratus Clouds. They may appear dense, dark, and rainy (or snowy) and can also be cottony white clumps interspersed with blue sky.

4) Great Vertical Extent Clouds • • •

They are most dramatic types of clouds. Great Vertical Extent Clouds are also known as the Storm Clouds. They rise to dramatic heights, and sometimes well above the level of transcontinental jetliner flights.

What is International Cloud Atlas? • • • •

The International Cloud Atlas describes the classification system for clouds and meteorological phenomena used by all World Meteorological Organization Members. It includes a manual of standards and photographs of clouds and weather phenomenon. It was first published in the 19th century and was last updated 30 years ago. The new 2017 version of International Cloud Atlas was a digitalized one and has many additions.

The new cloud classifications that were introduced the International Cloud Atlas (2017) 1) The Species Volutus • • • •

They are long, typically low, horizontal, detached, tube-shaped cloud mass. They often appear to roll slowly about a horizontal axis. The species volutus is a soliton and hence not attached to other clouds. This species applies mostly to Stratocumulus and rarely Altocumulus.

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2) The Supplementary Features (a) Asperitas • •

• •

There are well-defined, wave-like structures in the underside of the cloud. Asperitas is characterised by localised waves in the cloud base, either smooth or dappled with smaller features, sometimes descending into sharp points, as if viewing a roughened sea surface from below. The varying levels of illumination and thickness of the cloud can lead to dramatic visual effects. They occur mostly with Stratocumulus and Altocumulus.

(b) Fluctus • •

They are relatively short-lived wave formation, usually seen on the top surface of the cloud, in the form of curls or breaking waves (Kelvin-Helmholtz waves). They occur mostly with Cirrus, Altocumulus, Stratocumulus, Stratus and occasionally Cumulus.

(c) Cavum • •

•

These are a well-defined generally circular hole in a thin layer of supercooled water droplet cloud. The Cavum is typically a circular feature when viewed from directly beneath, but may appear oval-shaped when viewed from a distance. When resulting directly from the interaction of an aircraft with the cloud, it is generally linear. They occur in Altocumulus and Cirrocumulus and rarely Stratocumulus.

(d) Murus • • •

It is a localised, persistent, and often abrupt lowering of cloud from the base of a Cumulonimbus from which tuba (spouts) sometimes form. Usually associated with a supercell or severe multi-cell storm. Murus showing significant rotation and vertical motion may result in the formation of tuba (spouts), Commonly known as a ‘wall cloud’.

(e) Cauda • • •

A horizontal, tail-shaped cloud (not a funnel) at low levels extending from the main precipitation region of a supercell Cumulonimbus to the murus (wall cloud). It is typically attached to the wall cloud, and the bases of both are typically at the same height. Cloud motion is away from the precipitation area and towards the murus, with rapid upward motion often observed near the junction of the tail and wall clouds and are commonly known as a ‘tail cloud’.

3) Accessory Cloud Flumen

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•

• •

They are bands of low clouds associated with a supercell severe convective storm (Cumulonimbus), arranged parallel to the low-level winds and moving into or towards the supercell. These accessory clouds form on an inflow band into a supercell storm along the pseudo-warm front. One particular type of inflow band cloud is the ‘Beaver’s tail’. This is distinguished by a relatively broad, flat appearance suggestive of a beaver’s tail.

4) Special Clouds (a) Flammagenitus •

These are clearly observed to have originated as a consequence of localised natural heat sources (forest fires, wildfires or volcanic activity) and consist of water drops.

(b) Homogenitus • •

These are originated specifically as a consequence of human activity. They include aircraft condensation trails (contrails), or clouds resulting from industrial processes, such as cumuliform clouds generated by rising thermals above power station cooling towers.

(c) Homomutatus •

These are formed as a result of persistent contrails (Cirrus homogenitus) that may be observed, over a period of time and under the influence of strong upper winds, to grow and spread out over a larger portion of the sky, and undergo internal transformation such that the cloud eventually takes on the appearance of more natural cirriform cloud.

(d) Cataractagenitus • •

They may develop locally in the vicinity of large waterfalls as a consequence of water broken up into spray by the falls. The Cataractagenitus are formed when the downdraft caused by the falling water is compensated for by the locally ascending motion of air.

(e) Silvagenitus •

These are the clouds that may develop locally over the forests as a result of an increased humidity due to evaporation and evapotranspiration from the tree canopy.

What is Asperitas Cloud? • • •

Asperitas is formerly known as Undulatus asperitus. It is a cloud formation proposed by Gavin Pretor-Pinney of the Cloud Appreciation Society (2009). It is recently been accepted and added to the International Cloud Atlas on March 23, 2017, on the occasion of World Meteorological Day. 64

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• •

The ‘Asperitas’ is a Latin word and its meaning is ‘Rough‘. The Asperitas clouds tend to be low-lying and are caused by weather fronts that create undulating waves in the atmosphere.

Why clouds appear white in colour? •

The clouds usually appear white because the tiny water droplets and ice crystals inside them are tightly packed, and they reflect most of the sunlight that falls on these masses (scattering). The tiny cloud particles equally scatter all colours of light, which make the viewer to perceive all wavelengths of sunlight mixed together as white light.

•

Why do clouds darken at the time of rain? •

The clouds appear dark or grey in colour at the time of rain is due to their particulate density. The water vapour will bind together into raindrops, leaving larger spaces between these drops of water and hence less amount of light is reflected, lending a darker appearance of the rain clouds.

•

Evaporation And Condensation Evaporation •

Evaporation is a process by which water is converted from liquid to gaseous state.

•

Temperature is the main cause for evaporation.

•

The temperature at which the water starts evaporating is known as latent heat of vaporisation.

•

Rise in temperature escalates water absorption and retention capacity of the given parcel of air.

•

Movement of air substitutes the saturated layer with the unsaturated layer.

•

Hence, the greater the movement of air, the greater is the evaporation.

Condensation •

The conversion of water vapour into the water.

•

Condensation is caused by the loss of heat.

•

When moist air is cooled, it may reach a level when its capacity to hold water vapour terminates.

•

The surplus water vapour condenses into the liquid stage.

•

In free air, condensation results from cooling around very small particles named as hygroscopic condensation nuclei.

•

Condensation depends upon the amount of cooling and the relative humidity of the air.

•

It is influenced by the volume of air, temperature, pressure and humidity.

Condensation takes place:

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•

When the temperature of the air is decreased to dew point with its volume remaining constant.

•

When both the temperature and the volume are decreased.

•

When moisture is added to the air through evaporation. However, the most favourable circumstance for condensation is the reduction in air temperature.

Erosional landforms Valleys •

Valleys start as small and narrow rills. These rills will progressively develop into long and wide gullies.

•

The gullies will again deepen, widen and lengthen to give rise to valleys.

•

The valley types depend upon the type and structure of rocks in which they form.

•

Depending upon sizes and shapes, several types of valleys like V-shaped valley, gorge, canyon, etc. can be recognized.

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A gorge is a deep valley with very steep to straight sides.

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It is almost equal in width at its top as well as its bottom.

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A canyon is characterized by steep step-like side slopes and might be as deep as a gorge.

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It is a variant of the gorge.

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A canyon is wider at its top than at its bottom.

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It is commonly formed in horizontal bedded sedimentary rocks and gorges form in hard rocks.

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Potholes are cylindrical holes drilled into the bed of a river that varies in depth and diameter from a few centimetres to several metres.

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They are found in the upper course of a river where it has enough potential energy to erode vertically and its flow is turbulent.

Potholes

Plunge Pools •

A sequence of such depressions ultimately joins and the stream valley gets deepened.

•

At the foot of waterfalls also, large potholes, quite deep and wide, form because of the absolute influence of water and rotation of boulders.

•

These large and deep holes at the base of waterfalls are called plunge pools.

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These pools also help in the deepening of valleys.

Incised or Entrenched Meanders •

Entrenched meanders are symmetrical and form when the river down cuts quickly.

•

The speed of the river downcutting gives less opportunity for lateral Thus giving them symmetrical slopes.

•

These are very deep and wide meanders can also be found cut in hard rocks.

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•

It is common to find meandering courses over floodplains and delta plains where stream gradients are very gentle.

River Terraces •

River terraces are surfaces marking old valley floor or floodplain levels.

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They may be bedrock surfaces without any alluvial cover or alluvial terraces consisting of stream deposits.

•

•

Paired terraces: The river terraces may occur at the similar elevation on either side of the rivers.

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Unpaired terraces: When a terrace is present only on one side of the stream and with none on the other side or one at quite a different elevation on the other side.

The terraces may result due to •

Change in hydrological regime due to climatic changes.

•

Sea level changes in case of rivers closer to the sea.

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Receding water after a peak flow.

•

Tectonic uplift of land.

Glacial Depositional Landforms Various Glacial Depositional Landforms Glaciers have played an important role in the moulding of landscapes in the mid and high latitudes of alpine environments. The major depositional landforms made by glaciers are: •

Esker

•

Outwash plains

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Drumlins

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The esker is one of the most striking landforms of fluvioglacial deposition.

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They are usually formed of washed sand and gravel.

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Eskers vary in shape and size.

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When glaciers melt, the water flows on the surface of the ice or leaks down along the margins.

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These waters amass underneath the glacier and flow like streams in a channel beneath the ice. Such streams flow over the ground with ice forming its banks.

•

Very coarse materials like stones and blocks along with some minor segments of rock debris transported into this stream settle down in the valley of ice underneath the glacier and after the ice melts can be found as a winding ridge called Esker.

Eskers

Outwash Plains •

It is also known as called a sandur.

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It is a plain formed of glacial sediments deposited by meltwater outwash at the limit of a glacier. 67

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Drumlins •

These are smooth oval shaped ridge-like topographies composed primarily of glacial till with masses of gravel and sand.

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It forms due to the dumping of rock debris underneath heavily loaded ice through fissures in the glacier.

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The long axes of drumlins are parallel to the direction of ice movement.

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Drumlins give an indication of the direction of glacier movement.

•

The Stoss end is the steeper of the two ends and used to face into the ice flow.

Glacial Erosional Landforms Glaciers have played a prominent role in the shaping of landscapes in the mid and high latitudes of alpine environments. The major erosional landforms made by glaciers are •

Cirque

•

Horns and Serrated Ridges

•

Glacial Valleys/Troughs

•

Cirque is an amphitheatre-like valley formed by glacial erosion.

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They are long, deep, and wide troughs or basins with very steep concave to vertically dropping high walls on its head as well as sides.

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They are the commonly found of landforms in glaciated mountain especially at the heads of glacial valleys.

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The amassed ice cuts these cirques whereas moving down the mountain tops.

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A lake of water can be seen frequently inside the cirques after the glacier vanishes.

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Such lakes are called Cirque or tarn lakes.

Cirque

Horns and Serrated Ridges •

Horns form through headward erosion of the cirque walls.

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Horns form when three or more radiating glaciers cut the headward until their cirques meet high, sharp pointed and steep-sided peaks.

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The splits between Cirque side walls or head walls get narrow because of progressive erosion and turn into saw-toothed ridges occasionally mentioned to as arêtes with very sharp crest and a zig-zag outline.

•

Horns formed through headward erosion of radiating cirques are: •

The highest peak in the Alps

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Matterhorn

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The highest peak in the Himalayas Everest

Glacial Valleys/ Troughs •

They are U-shaped and trough-like with broad floors and comparatively smooth and steep edges.

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•

The valleys may comprise scattered debris or debris moulded as moraines with swampy

•

The very deep glacial troughs occupied with sea water and making up shorelines in high latitudes are known as fjords.

Types of Rainfall •

On the basis of origin, rainfall may be classified into three main types – the convectional, orographic or relief and the cyclonic or frontal.

Conventional Rainfall •

•

The, air on being heated, becomes light and rises up in convection currents. As it rises, it expands and loses heat and consequently, condensation takes place and cumulous clouds are formed. This process releases latent heat of condensation which further heats the air and forces the air to go further up. Convectional precipitation is heavy but of short duration, highly localised and is associated with minimum amount of cloudiness. It occurs mainly during summer and is common over equatorial doldrums in the Congo basin, the Amazon basin and the islands of south-east Asia.

Orographic Rainfall •

•

•

•

When the saturated air mass comes across a mountain, it is forced to ascend and as it rises, it expands (because of fall in pressure); the temperature falls, and the moisture is condensed. This type of precipitation occurs when warm, humid air strikes an orographic barrier (a mountain range) head on. Because of the initial momentum, the air is forced to rise. As the moisture laden air gains height, condensation sets in, and soon saturation is reached. The surplus moisture falls down as orographic precipitation along the windward slopes. The chief characteristic of this sort of rain is that the windward slopes receive greater rainfall. After giving rain on the windward side, when these winds reach the other slope, they descend, and their temperature rises. Then their capacity to take in moisture increases and hence, these leeward slopes remain rainless and dry. The area situated on the leeward side, which gets less rainfall is known as the rain-shadow area (Some arid and semi-arid regions are a direct consequence of rain-shadow effect. Example: Patagonian desert in Argentina, Eastern slopes of Western Ghats). It is also known as the relief rain. Example: Mahabaleshwar, situated on the Western Ghats, receives more than 600 cm of rainfall, whereas Pune, lying in the rain shadow area, has only about 70 cm.

The Wind Descending on the Leeward Side is heated adiabatically and is called Katabatic Wind. Frontal Precipitation •

When two air masses with different temperatures meet, turbulent conditions are produced. Along the front convection occurs and causes precipitation (we studied this in Fronts). For instance, in north-west Europe, cold continental air and warm oceanic air converge to produce heavy rainfall in adjacent areas. 69

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Cyclonic Rain • •

Cyclonic Rainfall is convectional rainfall on a large scale. (we will see this in detail later) The precipitation in a tropical cyclone is of convectional type while that in a temperate cyclone is because of frontal activity.

Monsoonal Rainfall •

This type of precipitation is characterized by seasonal reversal of winds which carry oceanic moisture (especially the south-west monsoon) with them and cause extensive rainfall in south and southeast Asia. (More while studying Indian Monsoons).

World Distribution of Rainfall •

Different places on the earth’s surface receive different amounts of rainfall in a year and that too in different seasons. In general, as we proceed from the equator towards the poles, rainfall goes on decreasing steadily. The coastal areas of the world receive greater amounts of rainfall than the interior of the continents. The rainfall is more over the oceans than on the landmasses of the world because of being great sources of water. Between the latitudes 35° and 40° N and S of the equator, the rain is heavier on the eastern coasts and goes on decreasing towards the west. But, between 45° and 65° N and S of equator, due to the westerlies, the rainfall is first received on the western margins of the continents and it goes on decreasing towards the east. Wherever mountains run parallel to the coast, the rain is greater on the coastal plain, on the windward side and it decreases towards the leeward side. On the basis of the total amount of annual precipitation, major precipitation regimes of the world are identified as follows. The equatorial belt, the windward slopes of the mountains along the western coasts in the cool temperate zone and the coastal areas of the monsoon land receive heavy rainfall of over 200 cm per annum. Interior continental areas receive moderate rainfall varying from 100 – 200 cm per annum. The coastal areas of the continents receive moderate amount of rainfall. The central parts of the tropical land and the eastern and interior parts of the temperate lands receive rainfall varying between 50 – 100 cm per annum. Areas lying in the rain shadow zone of the interior of the continents and high latitudes receive very low rainfall – less than 50 cm per annum. Seasonal distribution of rainfall provides an important aspect to judge its effectiveness. In some regions rainfall is distributed evenly throughout the year such as in the equatorial belt and in the western parts of cool temperate regions.

•

•

• • •

• • • •

Elements, Minerals and Rocks Elements In The Earth’s Crust • • •

The earth is composed of various kinds of elements. About 98% of the total crust is made up of eight elements as oxygen, silicon, aluminium, iron, calcium, sodium, potassium, and magnesium. The rest is constituted by elements like titanium, hydrogen, phosphorous, manganese, sulphur, carbon, nickel and others.

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• • •

The elements in the earth’s crust are rarely found exclusive but are usually combined with other elements to make various substances. These substances are recognised as minerals. The table below shows the percentage wise share of each element in both the earth’s crust and the whole earth.

Minerals in the Earth’s Crust • • • • • • •

A mineral is a naturally occurring organic or inorganic substance, having an orderly atomic structure and a definite chemical composition and physical properties. A mineral is composed of two or more elements. But, sometimes single element minerals like sulphur, copper, silver, gold, graphite, etc are also found. The basic source of all minerals is the hot magma in the interior of the earth. When magma cools, crystals of the minerals appear and a systematic series of minerals are formed in sequence to solidify so as to form rocks. The minerals which contain metals are called as metallic minerals (eg: Haematite) and the metallic minerals which are profitably mined are called as the ores. The crust of the earth is made up of more than 2000 minerals, but out of these, only six are the most abundant and contribute the maximum. These six most abundant minerals are feldspar, quartz, pyroxenes, amphiboles, mica and olivine.

Characteristics of some of the major minerals 1. Feldspar: • • • • •

Silicon and oxygen are major elements of all types of feldspar. Sodium, potassium, calcium, aluminium, etc are found in specific feldspar varieties. Half of the earth’s crust is composed of feldspar (plagioclase (39%) and alkali feldspar (12%)). It has light cream to salmon pink colour. It is commonly used in ceramics and glass making.

2. Quartz: • • • •

It is one of the most important components of sand and granite. It consists of silica and it is a hard mineral virtually insoluble in water. It is usually white or colourless. They are used in the manufacturing of radio, radar, etc.

3. Pyroxene: • • • •

The common elements in pyroxene are Calcium, aluminium, magnesium, iron and silicon. About 10% of the earth’s crust is made up of pyroxene. It is commonly found in meteorites. Its colour is usually green or black.

4. Amphibole:

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• • • •

Aluminium, calcium, silicon, iron and magnesium are the major elements of amphiboles. They form 7% of the earth’s crust. It is green or black in colour and is used in asbestos industries commonly. Hornblende is another form of amphiboles. 5.

• • • •

Mica:

It is made up of elements like potassium, aluminium, magnesium, iron, silicon, etc. It forms 4% of the earth’s crust. It is commonly found in igneous and metamorphic rocks. Mica is widely used in electronic instruments.

6. Olivine: • • •

Magnesium, iron and silica are the major elements of olivine. It is commonly found in basaltic rocks with a greenish colour. Olivine is used commonly in jewellery.

Rocks in the earth’s Crust • • • • •

A rock is nothing but a composition of minerals. They are aggregates or a physical mixture of one or more minerals. Rocks may be hard or soft and in varied colours. Feldspar and quartz are the most common minerals found in all type of rocks. The science dealing with the study of rocks is called as Petrology.

Classification of Rocks • •

As we said above, rocks differ in their properties, the size of particles and mode of formation. On the basis of mode of formation, rocks may be classified into three:

1. Igneous Rocks 2. Sedimentary Rocks 3. Metamorphic Rocks Igneous Rocks • • • • • •

Igneous rocks are formed by the cooling of highly heated molten fluid material called as Magma. Asthenosphere, which is just below the upper mantle, a region beneath Lithosphere is the main source of magma. They might be formed directly by cooling of magma from the interior of the earth itself or by cooling of lava from the surface of the earth. As they comprise the earth’s first crust and all other rocks are derived from them, they are also called as the parents of all rocks or the Primary Rocks. They are the most abundant rocks in the earth’s crust. On the basis of their mode of occurrence, igneous rocks can be classified as Intrusive and Extrusive Igneous Rocks.

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1. INTRUSIVE IGNEOUS ROCKS • •

They are formed when magma solidifies below the earth’s surface. The rate of cooling below the earth’s surface is very slow which gives rise to the formation of large crystals in the rocks. That is, the mineral grains of intrusive igneous rocks are very large. Deep-seated intrusive igneous rocks are called as Plutonic rocks and shallow depth intrusive igneous rocks are called as Hypabyssal Rocks. Eg: Granite, dolerite, etc.

• • •

2. EXTRUSIVE IGNEOUS ROCKS • • • • • • • •

They are formed by the cooling of the lava on the earth’s surface. As lava cools very rapidly on the surface, the mineral crystals forming extrusive igneous rocks are very fine. These rocks are also called as Volcanic Rocks. Eg: Gabbro, Basalt, etc. On the basis of chemical properties, igneous rocks can be classified as Acid and Basic Igneous rocks. They are formed as a result of solidification of acidic (high viscous) or basic lava (low viscous). Acidic igneous rocks are composed of 65% or more of silica. They are coloured, hard and very strong (Eg: Granite). Basic igneous rocks contain less than 55% of silica and have more iron and magnesium. They are dark in colour, weak enough for weathering (Eg: Basalt, Gabbro).

Sedimentary Rocks • • • • •

These rocks are formed by successive deposition of sediments. These sediments may be the debris eroded from any previous existing rock which may be igneous, metamorphic or old sedimentary rocks. The process of successive deposition and formation of sedimentary rocks is called as Lithification. Due to successive depositions, they have a layered or stratified structure and hence are also called as Stratified Rocks. Depending upon the mode of formation, sedimentary rocks can be classified as:

1. Mechanically formed/ Clastic Sedimentary Rocks • •

They are formed by the consolidation of sediments under excessive pressure and cementation. Eg: Conglomerate, Breccia, Sandstone, Shale, etc.

2. Organically/ Biologically formed Sedimentary Rocks • •

The consolidation of organic matters derived from plants and animals form this type of rocks. Eg: Coal, limestone, chalk, chert, etc.

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3. Chemically formed Sedimentary Rocks • •

They are formed by various chemical reactions. Eg: Gypsum, rock salt, limestone, etc.

Metamorphic Rocks • • • • • •

• • •

The word metamorphic means ‘change of form’. Hence, these rocks form under the action of temperature, pressure and volume changes on original rocks. Metamorphic rocks are formed under the influence of heat or pressure on original rocks which cause to change their colour, hardness, structure and composition. The process of recrystallization and reorganisation of materials within the original rock is called as metamorphism. When the metamorphism happens without any appreciable chemical change, it is called as Dynamic Metamorphism. If metamorphism happened due to the influence of heat, it is called as Thermal Metamorphism. It has two types: Contact Metamorphism and Regional Metamorphism. When the reorganisation occurs due to direct contact with the hot magma, it is called as Contact Metamorphism. If the rocks undergo reorganisation due to tremendous heat/ pressure formed as a result of tectonic shearing, it is called as Regional Metamorphism. Metamorphic Rocks can be classified into Foliated (Slate, Schist, Gneiss) and NonFoliated (Quartzite, Marble) Metamorphic Rocks on the basis of the presence or absence of bands of mineral grains.

Rock Cycle • •

Rocks do not remain in their original form for a long time but may undergo transformations. The rock cycle is a continuous process through which old rocks are transformed into new ones as shown in the diagram below.

Summary • •

•

•

“Crust” describes the outermost shell earth. Our planet’s thin, 40-kilometer deep crust—just 1% of Earth’s mass—contains all known life in the universe. Oceanic crust is mostly composed of different types of basalts. Geologists often refer to the rocks of the oceanic crust as “sima.” Sima stands for silicate and magnesium, the most abundant minerals in oceanic crust. Continental crust is mostly composed of different types of granites. Geologists often refer to the rocks of the continental crust as “sial.” Sialstands for silicate and aluminum, the most abundant minerals in the continental crust. Sial can be much thicker than sima (as thick as 70 kilometers kilometers), but also slightly less dense (about 2.7 grams per cubic centimeter).

Minor Relief of the Ocean floor Minor Relief 74

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The ocean floors can be divided into four major divisions and some minor relief features in the ocean floors like •

Mid-Oceanic Ridges

•

Seamounts

•

Guyots

•

Trenches

•

Canyons

Mid-Oceanic Ridges •

A mid-oceanic ridge is an underwater mountain range, formed by plate tectonics.

•

It is composed of two chains of mountains divided by a large depression.

•

The mountain ranges can have peaks as high as 2,500 m and some even reach above the ocean’s surface.

•

Examples for Mid-oceanic ridges: •

Mid-Atlantic Ridge, Atlantic Ocean

•

East Pacific Rise

•

Pacific-Antarctic Ridge

Seamount •

Seamounts are mountains with pointed peaks, mounting from the seafloor, and that do not reach the surface of the ocean.

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They are volcanic in origin.

•

Seamounts can be 3,000-4,500 m tall.

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An extension of the Hawaiian Islands in the Pacific Ocean which is known as The Emperor seamount is an example of seamount.

Submarine Canyons •

Submarine Canyons are a kind of narrow steep-sided valleys.

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It originates either within continental slopes or on a continental shelf.

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Congo Canyon is regarded as the largest river canyon.

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The Hudson Canyon is the best-known submarine canyon in the world.

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The largest submarine canyon in the world is Zhemchug Canyon.

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It is a flat topped seamount.

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It is also known as a table mount.

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They show evidence of slow subsidence through stages to become flat-topped submerged mountains.

•

It is expected that more than 10,000 guyots and seamounts occur in the Pacific Ocean only.

Guyots

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Atoll •

It is a ring-shaped coral reef containing a coral rim that encompasses a lagoon incompletely or completely.

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These are low islands found in the tropical oceans.

•

It may be a part of the sea (lagoon), or occasionally form encircling a body of brackish, fresh, or highly saline water.

Ocean Floor And Its Features Divisions of the Ocean Floors An oceanic basin is the land surface under an ocean that includes the topography under the water. The ocean floors can be divided into four major divisions: •

The Continental Shelf

•

The Continental Slope

•

The Deep Sea Plain

•

The Trenches

Minor relief features in the ocean floors Besides, the major divisions, there are also major and minor relief features in the ocean floors like •

Ridges

•

Hills

•

Seamounts

•

Guyots

•

Trenches

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Canyons

Continental Shelf •

The continental shelf is the stretched margin of all continent occupied by comparatively shallow gulfs and sea.

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It is the shallowest part of the ocean

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The shelf normally ends at a very steep slope which is called the shelf break.

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The average width of continental shelves is about 80 km.

•

The Continental shelves are very narrow or almost absent along certain margins like the •

Coasts of Chile

•

The west coast of Sumatra

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The Siberian shelf in the Arctic Ocean is the largest in the world

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Enormous sedimentary deposits received over a long time by the continental shelves, turn out to be the source of fossil fuels.

Continental Slope 76

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The continental slope links the continental shelf and the ocean basins.

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It starts where the bottom of the continental shelf abruptly drops off into a steep slope.

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Canyons and trenches are seen in this region.

Deep Sea Plain •

Deep sea plain is gently sloping areas

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These are the flattest and flattest areas

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These plains are completely covered with fine-grained deposits like silt and clay.

Oceanic Deeps or Trenches •

Trenches are the deepest parts of the oceans.

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The trenches are comparatively steep-sided and have narrow basins.

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They are some 3-5 km deeper than the adjacent ocean floor.

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They are found at the bases of continental slopes and along island arcs

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Trenches are associated with active volcanoes and strong earthquakes.

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That is why they are very important in the study of plate movements.

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