Geography E-Book PDF

UDAAN PRELIMS WALLAH (STATIC) GEOGRAPHY QUICK AND COMPREHENSIVE REVISION SERIES FOR PRELIMS 2024 Published By: Physicswallah Private Limited Physics Wallah Publication ISBN: 978-93-6034-405-4 MRP: 239/- Mobile App: Physics Wallah (Available on Play Store) Website: https://www.pw.live;https://pwonlyias.com/ Email: [email protected] Rights All rights are reserved with the Publisher Disclaimer A team of PW OnlyIAS experts and faculties with a deep understanding of the subject has worked hard for the creation and curation of this book. While the content creators, editors and publisher have used their best efforts in preparing these books. The content has been checked for accuracy. As the book is intended for educational purposes, the author shall not be responsible for any errors contained in the book. The publication has designed the content to provide accurate and authoritative information with regard to the subject matter covered. (This Book shall only be used for educational purposes.) PREFACE A highly skilled professional team of PW ONLY IAS works arduously to ensure that the students receive the best content for the UPSC exam. A plethora of UPSC study materials are available in the market, but PW ONLY IAS professionals continuously work to provide supreme-quality study material for our UPSC students. From the beginning, the whole content team comprising Content Creators, Reviewers, DTP operators, Proofreaders and others are involved in shaping the material to their best knowledge and experience to produce powerful content for the students. Faculties have adopted a new style of presenting the content in easy-to-understand language and have provided the team with guidance and supervision throughout the creation of this book. PW ONLY IAS strongly believes in conceptual and fun-based learning and provide highly exam-oriented content to bring quality and clarity to the students. This book adopts a multi-faceted approach to mastering and understanding the concepts and equipping the students with the knowledge for this competitive exam. The main objective of the study material is to provide short, crisp, concise and high-quality content to our students. BOOK FEATURES z Holistic coverage of topics, strictly as per exam syllabus. z One-stop solution for prelims based, subject-wise coverage. z Diagrams and Timelines for quick understanding and revision. z Quick Revision Module for the UPSC Prelims examination. z Every topic is structured in headings and bullets for easy understanding of the students. CONTENTS 1. THE ORIGIN AND EVOLUTION Distribution of Volcanoes................................................9 OF THE EARTH.......................................1 Volcanic Landforms............................................................9 z Theories of Earth Origin............................................... 1 z Earth’s Geomagnetic Field.........................................10 Early Theories......................................................................1 Causes of Geomagnetic Field.......................................10 Modern Theories.................................................................1 Geomagnetic Reversal....................................................10 z Star Formation.................................................................. 1 Geomagnetic Poles...........................................................10 z Formation of Planets...................................................... 1 Significance of Geomagnetic Field............................10 z Our Solar System.............................................................. 1 Magnetosphere..................................................................10 z Earth 2 Magnetic Storm.................................................................10 Origin of Life..........................................................................2 Latitude...................................................................................2 z Geological Timescale....................................................11 Longitudes (Meridian)......................................................2 3. DISTRIBUTION OF OCEANS AND Standard Time......................................................................3 Eclipse......................................................................................4 CONTINENTS 12 z Continental Drift Theory.............................................12 2. INTERIOR OF THE EARTH.....................5 Wegener’s Proposition...................................................12 z Structure of the Earth’s Interior................................. 5 Evidence in Support of the Continental Drift.......12 Crust..........................................................................................5 z Post-Drift Studies..........................................................12 Mantle......................................................................................5 Core...........................................................................................5 Convectional Current Theory of z Composition of the Earth.............................................. 5 Arthur Holmes...................................................................12 Minerals...................................................................................5 Concept of Seafloor Spreading...................................12 Rocks........................................................................................6 Hess’s Seafloor Spreading Hypothesis....................12 Types of Rocks......................................................................6 z Plate Tectonics................................................................13 z Earthquakes...................................................................... 7 Division of Plates..............................................................13 Earthquake Waves..............................................................7 Force Behind the Plate Movement............................13 Shadow Zone.........................................................................8 Plate Boundaries.............................................................13 Types of Earthquakes........................................................8 z Movement of the Indian Plate...................................14 Distribution of Earthquakes...........................................8 z Volcanoes and Volcanic Landforms........................... 8 Indian Plate Boundaries................................................14 Causes of Volcanic Eruption..........................................8 Historical Progression of the Indian Plate.............14 Classification of Volcanoes..............................................8 z Isostacy 14 4. GEOMORPHIC PROCESSES................15 8. ATMOSPHERIC CIRCULATION z Geomorphic Processes................................................15 AND WEATHER SYSTEMS 31 Endogenic Forces (Land Building Forces).............15 Distribution of Air Pressure.........................................31 Exogenic Forces (Land Wearing Forces)................15 Forces Affecting the Velocity and Direction z Mass Movements............................................................17 of Wind..................................................................................31 Landslide..............................................................................17 z General Circulation of the Atmosphere..................31 Global Pressure Belts......................................................31 5. LANDFORMS AND THEIR Pressure Cells.....................................................................33 EVOLUTION 18 z Geostrophic Winds........................................................33 Jet Streams..........................................................................33 z Running Water................................................................18 z Classification of Winds................................................34 Erosional Landforms.................................................18 Planetary Winds...............................................................34 Depositional Landforms................................................19 Periodic Winds..................................................................34 z Groundwater...................................................................20 Local Winds........................................................................35 Erosional Landforms......................................................20 z Air Masses........................................................................35 Depositional Landforms................................................20 Source Region....................................................................35 z Glaciers 21 Types of Air Mass.............................................................36 Glacial Erosional Landforms.......................................21 Fronts....................................................................................36 Glacial Depositional Landforms.................................22 z Cyclones 36 z Coastal Landforms........................................................22 Temperate Cyclones........................................................37 Coastal Erosional Landforms......................................23 Tropical Cyclones.............................................................37 Coastal Depositional Landforms................................23 Special Cyclones................................................................38 z Winds 24 Thunderstorms and Tornadoes.................................38 Desert Erosional Landforms........................................24 Polar Vortex.......................................................................38 Desert Depositional Landforms.................................25 9. WATER IN THE ATMOSPHERE.............39 6. COMPOSITION AND STRUCTURE z Humidity...........................................................................39 OF ATMOSPHERE...............................26 z Evaporation and Condensation.................................39 z Composition of the Atmosphere...............................26 Evaporation.........................................................................39 Layers of Atmosphere....................................................27 Condensation.....................................................................40 z Clouds 40 7. SOLAR RADIATION, HEAT Types of Clouds.................................................................40 BALANCE AND TEMPERATURE..........28 Other Clouds.......................................................................41 z Solar Radiation & Insolation.....................................28 z Precipitation...................................................................41 Distribution of Solar Radiation..................................28 Types of Rainfall...............................................................42 Spatial Distribution of Insolation on World Distribution of Rainfall.....................................42 Earth’s Surface...................................................................28 z Heating and Cooling of Atmosphere........................28 10. WORLD CLIMATE AND CLIMATE z Heat Budget of the Planet Earth...............................29 CHANGE 43 z Temperature...................................................................29 z World Climate and its Classification.......................43 Factors Controlling Temperature Distribution....29 Hot, Wet Equatorial Climate........................................43 Temperature Inversion..................................................30 Tropical Monsoon............................................................43 vi Tropical Marine Climate................................................44 Vertical Distribution of Salinity..................................54 Savanna or Sudan Climate............................................44 Salinity of Marginal Seas...............................................54 Desert Climate...................................................................44 z Ocean Water Circulation.............................................54 Hot Desert Climate...........................................................45 Waves.....................................................................................54 Mid-Latitude Desert Climates.....................................45 Tides......................................................................................54 Warm Temperate Western Margin Ocean Currents..................................................................55 (Mediterranean) Climate..............................................45 z Key Terms.........................................................................57 Temperate Continental (Steppe) Climate..............46 12. INDIA-LOCATION...............................58 Warm Temperate Eastern Margin (China Type).......................................................................47 z India and its Neighbours.............................................58 z India’s Geographical Extent.......................................58 Cool Temperate Western Margin (British Type).....................................................................48 13. STRUCTURE AND Cool Temperate Eastern Margin PHYSIOGRAPHY 59 (Laurentian).......................................................................48 z Major Geological Divisions of India.........................59 The Cool Temperate Continental Climate z Physiography of India.................................................60 (Siberian).............................................................................48 z Northern and Northeastern Mountains.................60 Arctic or Polar or Tundra Climate.............................49 North-South Division of Himalayas..........................60 East-West Division of Himalayas...............................61 11. OCEAN AND ITS MOVEMENT............50 Eastern Hills and Mountains.......................................62 z Relief of the Ocean Floor.............................................50 z Northern Plains..............................................................62 Continental Shelf..............................................................50 z Peninsular Plateau........................................................62 Continental Slope.............................................................51 Deccan Plateau..................................................................63 Continental Rise................................................................51 Central Highlands.............................................................63 Northeastern Plateau....................................................63 Deep Sea Plain or Abyssal Plain.................................51 Western Ghats....................................................................63 Oceanic Deeps or Trenches..........................................51 Eastern Ghats.....................................................................64 Mid-Oceanic Ridges.........................................................51 z Indian Desert..................................................................64 Minor Relief Features.....................................................51 z Coastal Plains..................................................................64 Other Relief Features......................................................52 Western Coastal Plains...................................................64 z Temperature of Ocean Waters..................................52 Eastern Coastal Plains...................................................64 Factors Affecting Temperature of z Islands 65 Ocean Waters.....................................................................52 Bay of Bengal Islands......................................................65 Arabian Sea Islands.........................................................65 Vertical Distribution of Temperature in Oceans..............................................................................52 14. DRAINAGE SYSTEM............................66 Horizontal Temperature Variations.........................53 z Major Drainage Systems..............................................66 z Salinity of Ocean Waters........................................53 Sequent Drainage Systems...........................................66 Factors Affecting Ocean Salinity................................53 Insequent Drainage Systems.......................................66 Horizontal Distribution of Salinity...........................54 z Types of Drainage Patterns........................................66 vii z Indian Drainage System..............................................67 17. SOILS..................................................81 z Himalayan Drainage............................................67 z Soil Forming Factors.....................................................81 Characteristics...................................................................67 z Classification of Soils....................................................81 Indus River System..........................................................67 Alluvial Soils.......................................................................81 Tributaries of the Indus River.....................................68 Black Soil..............................................................................81 Ganga River System.........................................................68 Red and Yellow Soil.........................................................82 Course of the Ganga River............................................68 Laterite Soil.........................................................................82 Tributaries of the River Ganga....................................69 Brahmaputra System......................................................69 Arid Soil................................................................................82 Tributaries of the River Brahmaputra.....................70 Saline Soils..........................................................................82 z Peninsular Drainage System.............................70 Peaty Soils............................................................................82 Evolution of Peninsular Drainage System..............70 Forest Soils..........................................................................83 River Systems of the Peninsular Drainage.............70 z Soil Erosion......................................................................83 z Soil Conservation...........................................................83 15. CLIMATE..............................................72 z Factors Affecting India’s Climate..............................72 18. NATURAL VEGETATION.....................84 Factors Related to Location and Relief....................72 z Tropical Wet Evergreen...............................................84 Factors Related to Air Pressure and Wind............72 z Tropical Semi Evergreen Forests..............................84 z Seasons in India.............................................................72 z Tropical Deciduous Forests........................................84 Cold Weather Season......................................................72 z Tropical Thorn Forests................................................84 Hot Weather Season........................................................73 z Montane Forests.............................................................85 South-West Monsoon Season......................................74 z Mangroves........................................................................85 Retreating Monsoon Season z Sacred Groves.................................................................85 (The Transition Season)................................................75 z Social Forestry................................................................85 Characteristics of Monsoon Rainfall........................75 z Traditional Indian Seasons........................................76 19. RESOURCES........................................87 z Distribution of Rainfall................................................76 z Land Resources and Agriculture..............................87 z Variability of Rainfall...................................................76 Land use Categories........................................................87 z Climatic Regions of India............................................76 Operational Land Holding in India...........................87 Types of Agriculture........................................................87 16. N ATURAL HAZARDS AND Cropping Seasons in India............................................88 DISASTERS 78 Major Crops in India........................................................88 z Classification of Natural Disasters...........................78 z Minerals 91 Earthquakes........................................................................78 Mode of Occurrence of Minerals................................91 Tsunami................................................................................79 Global Distribution of Minerals..................................92 Tropical Cyclone...............................................................79 Distribution of Minerals in India..............................93 Floods....................................................................................80 Ferrous Minerals...............................................................95 Droughts...............................................................................80 Non-Ferrous Minerals....................................................95 Landslides............................................................................80 Non-metallic Minerals...................................................96 viii z Energy Resources..........................................................97 21. TRADE, TRANSPORT AND Non-Conventional Renewable COMMUNICATION 103 Sources of Energy............................................................97 z Road Transport in India...........................................103 Conventional Sources of Energy................................97 Unconventional Hydrocarbons...................................99 Classification of Roads in India...............................103 z Water Resources............................................................99 z Pipelines in India........................................................104 z Water Transport.........................................................105 20. MANUFACTURING INDUSTRIES.....100 Oceanic Waterways/Sea Routes............................105 z Classification of Industries......................................100 Inland Waterways in India........................................106 z Location of Industries...............................................100 z Industrial Corridors..................................................107 z Agro-Based Industry.................................................101 z International Connectivity Projects.....................107 Textile Industry..............................................................101 Sugar Industry................................................................101 22. POPULATION AND z Mineral Based Industries........................................101 SETTLEMENTS 108 Iron and Steel Industry...............................................101 z Population: Distribution, Density Aluminium Smelting....................................................102 and Growth...................................................................108 Fertilizer Industry.........................................................102 Introduction.....................................................................108 Petrochemical Industries...........................................102 India’s Population.........................................................108 Cement Industry............................................................102 Census 2011 (15th Census)......................................109 Automobile Industry....................................................102 z Settlements...................................................................110 z Major Industrial Regions.........................................102 Urbanisation in India...................................................110 ix 1 The Origin and Evolution of The Earth These formed the basis for the development of THEORIES OF EARTH ORIGIN z galaxies. A galaxy contains a large number of stars. Early Theories z A galaxy starts to form through the accumulation of hydrogen gas in the form of a very large cloud called z Nebular Hypothesis: German philosopher Immanuel a nebula. Kant gave the theory known as Nebular Hypothesis and Mathematician Laplace revised it in 1796. It said z Eventually, growing nebulae develop localised clumps that the planets were formed out of slowly rotating of gas. clouds of material associated with a youthful sun. z These clumps continue to grow into even denser z Revised Nebular Hypothesis: Given by Otto Schmidt gaseous bodies, giving rise to the formation of stars. (Russia) and Carl Weizascar (Germany). It said that the sun was surrounded by solar nebulae containing FORMATION OF PLANETS mostly hydrogen, helium, and dust formed due to the friction and collision of particles. The planets formed z The stars are localised lumps of gas within a nebula. through the Process of Accretion. The gravitational force within the lumps leads to the formation of a core to the gas cloud and a huge z Planetesimal Hypothesis: Given by Chamberlain rotating disc of gas and dust develops around the and Moulton in 1900, later supported by Sir James gas core. Jeans and later Sir Harold Jeffrey. According to this, a wandering star approached z In the next stage, the gas cloud starts getting the Sun. condensed and the matter around the core develops into small rounded objects. A cigar-shaped extension of material was separated from the solar surface. z These small-rounded objects formed by the process of cohesion develop into what is called planetesimals As the passing star moved away, the material (large numbers of smaller bodies). separated from the solar surface continued to revolve around the sun and it slowly condensed z Larger bodies start forming by collision, and into planets gravitational attraction causes the material to stick together. Modern Theories z In the final stage, these large numbers of small z Big Bang Theory or Expanding Universe planetesimals accrete to form fewer large bodies in Hypothesis: Formulated by Georges Lemaitre; the form of planets. strengthened by Edwin Hubble’s observations and the discovery of cosmic microwave background OUR SOLAR SYSTEM radiation (CMB) by Penzias and Wilson. It states that 13.8 billion years ago, ‘tiny ball’ Solar system is a celestial system, including a star and exploded and later expansion of universe took orbiting objects, bound by gravity. Our solar system place. consists of the Sun (central star), 8 planets, millions of smaller bodies like asteroids and comets and huge Energy was converted to matter during growth. quantities of dust-grains and gases. It orbits the Milky z An alternative to the expansion of the universe was Way Galaxy and is located in the Milky Way’s outer spiral Hoyle’s concept of steady state which considered the arm (Orion), disc-shaped. universe to be roughly the same at any point of time. z Inner or Terrestrial Planets: Higher densities, smaller in size, and their lower gravity could not STAR FORMATION hold the escaping gases; Formed in close vicinity of z The distribution of matter and energy was uneven in the sun, it was too warm for gases to condense to the early universe. These initial density differences solid particles. Intense solar winds blew off gases in gravitational forces caused the matter to get and dust, thus, leading to formation of Solid rocky drawn together. surface. E.g., Mercury, Venus, Earth and Mars. z Outer or Jovian Planet: Lower densities and bigger Origin of Life in size; Formed at a distant location from the Sun, z Initially the earth’s atmosphere was not conducive less intense solar winds resulted in retention of gases for the development of life. There was hardly any and formation of Dusty gaseous surface. E.g., Jupiter, atmosphere on Earth when it was created 4.6 billion Saturn, Uranus and Neptune. years ago. z Atmosphere was mostly created by gasses released by z Eight planets: Mercury, Venus, Earth, Mars, Jupiter, volcanoes. It contained methane, hydrogen sulfide, Saturn, Uranus and Neptune. and between 10 and 200 times the amount of carbon z Mercury : smallest and nearest to the Sun. dioxide found in the atmosphere today. [UPSC 2018] z Venus is considered as Earth’s-twin (similar shape z The process through which the gases were outpoured and size). It is probably the hottest planet (the from the interior is called degassing. atmosphere contains 90-95% of carbon dioxide with z The record of life that existed on this planet in different periods is found in rocks in the form of fossils. clouds of Sulphuric acid). z The microscopic structures closely related to the z Jupiter is the largest planet in the solar system. Its present form of blue algae have been found in atmosphere contains hydrogen, helium, methane geological formations much older than some 3,000 and ammonia. million years. It can be assumed that life began to z The tilt of the rotational axis of Venus and Uranus is so evolve sometime 3,800 million years ago. great that these planets actually rotate in a direction Latitude that is opposite to the other planets. Latitude is the angular distance of a point on the earth’s surface, measured in degrees from the Centre of the Moon earth; Parallel to the equator therefore called parallels The Moon is the only natural satellite of the Earth. Its of latitude with unequal diameters. diameter is only one-quarter that of the Earth. z The linear distance of a degree of latitude at the z The moon is tidally locked to the earth, meaning pole is somewhat longer than that at the equator due to the earth’s minor flattening at the poles. that the moon revolves around the earth in about 27 days which is the same time it takes to complete one Important Parallels of Latitudes rotation. As a result of tidal locking, only one side of z Tropic of Cancer (23½° N) in the Northern Hemisphere. the moon is visible to us on the earth. It passes through - North America: Bahamas z Generally it is believed that the formation of the Moon (Archipelago), Mexico; Africa: Egypt, Libya, Niger, Algeria, Mali, Western Sahara, Mauritani; Asia: is an outcome of giant impact or what is described as Taiwan, China, Myanmar, Bangladesh, India, Oman, the big splat. UAE, Saudi Arabia. z Super Moon: When the moon is at the minimum z Tropic of Capricorn (23½° S) in the Southern distance to the earth; Also referred to as perigee Hemisphere. or full moon. Moon appears 14% larger and 30% It passes through South America: Argentina, brighter. Brazil, Chile, Paraguay; Africa: Namibia, Botswana, South Africa, Mozambique, Madagascar; Australia. EARTH z Arctic Circle at 66½° in North of the equator. z Antarctic Circle at 66½° in South of the equator. Earth is the fifth largest planet in the Solar system; also z Largest circle is the Equator (0° latitude) while at the called Blue Planet as two-thirds surface is covered by poles they shrink to a point (90° N &S). water. z Equator passes through - South America: Ecuador, z Shape: Geoid (oblate spheroid) - slightly flattened at Colombia, Brazil; Africa: Sao Tome and Principe, the Poles and bulging at the Equator. Gabon, Congo, Democratic Republic of Congo, Uganda, z Earth lies in the Goldilocks Zone - water can exist in Kenya, Somalia; Asia: Maldives, Indonesia, Kiribati. a liquid state. Longitudes (Meridian) z Densest planet in the solar system. The longitude of a place is an angular distance east or z Speed of rotation around the axis is maximum at the west of the Prime Meridian (measured in degrees - 0° equator and decreases poleward. to 180°). They are semicircles running from the North z The axis of the earth, which is an imaginary line, Pole to the South Pole. Each degree is further divided makes an angle of 66½° with its orbital plane. into minutes, and minutes into seconds. 2 The Origin and Evolution of The Earth z Prime Meridian: In 1884, it was decided to choose Motion of Earth as zero meridian the one which passes through the z Rotation: Movement of the earth around its axis Royal Astronomical Observatory at Greenwich, near from west to east. Speed of rotation at equators is London as a Prime Meridian greater than at poles. It passes through - Europe: UK, France, Spain; Africa: Algeria, Mali, Burkina Faso, Ghana, Togo; THE EARTH’S INCLINATION ON ITS AXIS Antarctica. Right Angle Magnetic pole to Orbit of Earth z International Date Line: 180° longitude is chosen Axis of rotation as the International Date Line. The International Date 10° Line in the mid-Pacific curves from the normal 180° Equatorial Axis 23½° South Magnetic Pole North Magnetic Pole meridian at the Bering Strait, Fiji, Tonga and other islands to prevent confusion of day and date in some of the island groups that are cut through by the meridian. Tropic of Cancer A traveller crossing the Date Line from east to west loses a day and while crossing the Date Line Director of Equatorial Axis from west to east he gains a day. Tropic of Capricorn The west side of the line is always one day ahead of the Eastern side South Geographical Pole z Distance between longitudes decreases steadily ½° North Magnetic Pole 23½° from Equator to Poles until it becomes zero at the poles, where all the meridians meet (Maximum at the Inclination equator). Effects: Cycle of day & night and Coriolis Force z The circle that divides the day from night on the z Revolution: Movement of the earth around the sun globe is called the circle of illumination. This circle in an elliptical path. Distance from the sun is closest does not coincide with the axis. on 3rd Jan (Perihelion) and farthest on 4th July (Aphelion). Standard Time Effects: Varying length of day and night and The local time of places which are on different meridians Seasonality, both because of the tilt of the axis. is bound to differ. In India, for instance, there will be a Seasons change due to the change in the position difference of about 1 hour and 45 minutes in the local of the earth around the sun (Revolution) [UPSC times of Dwarka (Gujarat) and Dibrugarh (Assam). 2013]. z In India, the longitude of 82½° E (82° 30’E) is treated Places beyond the Arctic Circle experience as the standard meridian. The local time at this continuous daylight for about six months. meridian is taken as the standard time for the whole country [Indian Standard Time (IST)]. Solstice: During Solstice, the Sun shines directly over z India located east of Greenwich at 82°30’E is 5 hours one of the tropics. [UPSC 2022 and 2019] and 30 minutes ahead of GMT. z Summer Solstice: When one of the poles of the Earth has its maximum tilt towards the Sun; Heat Zones of Earth Northern Hemisphere - on June 21 and Southern z The mid-day sun is exactly overhead at least once Hemisphere - on December 22; Longest day. a year on all latitudes in between the Tropic of z Winter Solstice: When one of the poles of the Earth Cancer and the Tropic of Capricorn. This area, has its maximum tilt away from the Sun; Northern therefore, receives the maximum heat and is called Hemisphere — on December 22 and Southern the Torrid Zone. Hemisphere — on June 21; Shortest day. z Areas between the Tropic of Cancer and the Arctic Equinox: When the sun shines directly over the Circle in the Northern Hemisphere, and the Tropic of Equator - equal lengths of day and night at all points Capricorn and the Antarctic Circle in the Southern on Earth; Occurs twice in a year. Hemisphere, are called Temperate Zones. z 21 March (Spring in Northern hemisphere and z Areas lying between the Arctic Circle and the North Pole in the Northern Hemisphere and the Antarctic autumn in southern hemisphere); Circle and the South Pole in the Southern Hemisphere z 23 September (Autumn in Northern hemisphere are called Frigid Zone. and spring in Southern Hemisphere). The Origin and Evolution of The Earth 3 Equal Day and Night 66½° Equator Arctic Circle March 21 st Arctic Circle (Daylight) (Spring Equinox) (Darkness) Cancer st nd June 21 December 22 (Summer Solstice) SUN (Winter Solstice) rd Antarctic Circle September 23 Antarctic Circle (Darkness) (Autumn Equinox) (Daylight) Eq ’s Orbit Earth ua tor Equal Day and Night Eclipse It is defined as an astronomical phenomenon which occurs when one spatial object comes within the shadow of another spatial object. It happens when three celestial bodies are in a straight line called syzygy. Types of Eclipse Solar Eclipse Lunar Eclipse When moon passes in Moon passes through front of the sun the Earth’s Shadow (Observed from Earth) Occur on new Occur only during moon phase full moon On basis of distance of Depending upon the positioning moon from Earth-3 of Sun, Moon and Earth-2 Stages of Solar Eclipse Types of lunar eclipse Partial Annuals Total Partial Total Sun, Moon and Sun can be seen Sun is completely Part of moon When Moon and Sun Earth not around the edges blocked by moon moves into shadow are exactly opposite exactly lined up moon is of Earth side of Earth Sun, Moon Earth Only a portion Full Shadow on a direct line of sunlight is blocked Timeline Event 13.7 billion years ago Event of big bang 5-6 billion years ago Formation of stars 4.6 billion years ago Planets were formed 4.4 billion years ago Moon was formed 4000 million years ago Formation of oceans 3800 million years ago Life began to evolve 2500-3000 million years ago Process of Photosynthesis got evolved v v v 4 The Origin and Evolution of The Earth 2 Interior of The Earth z Upper portion of the mantle is called the STRUCTURE OF THE EARTH’S INTERIOR asthenosphere (main source of magma). The structure of the Earth’s interior is made up of z Density is higher than the continental crust. several concentric layers. Temperature and pressure z Mohorovicic Discontinuity: boundary between increase as we go deeper towards the centre of the lower crust and upper mantle. Earth because of the presence of radioactive materials. z Repetti Discontinuity: transition zone between upper mantle and lower mantle. Broadly, three layers can be identified: z Lithosphere: This solid layer comprises the crust Crust and the uppermost part of the mantle. Its thickness z Earth’s outermost layer which is solid and brittle. varies between 10 km and 200 km. z Lower Mantle: Positioned below the asthenosphere, z Continental Crust: mean thickness = 30 km & density remains solid, extending down to the Earth’s core. = 2.7g/cm3; Rock Type: Granite; Minerals - Silica + Aluminium = SIAL Core z Conrad discontinuity: boundary between upper z Starts at a depth of 2,900 km; crust and lower crust. z The outer core is liquid, mainly because of its z Oceanic Crust: Thinner than Continental Crust, Mean high temperature, while the inner core remains Thickness = 5km & density = 3g/cm3; Rock type: solid despite even greater temperatures due to the Basalt; Minerals mean thickness = Silica + Iron + immense pressures at this depth. Magnesium = SIMA z Composition: Predominantly made up of heavy materials i.e. “nife” layer (Nickel and Iron) Internal Structure of The Earth z Gutenberg Discontinuity: transition zone between Density Depth (Km) lower mantle and outer core. 2-90 Conrad Discontinuity 0 z Lehmann Discontinuity: transition zone between 30 outer and inner cores. 3-3 Mohorovicic Discontinuity 200 Sources to study the interior of the earth: Direct- surface 4-3 Repetti 700 rocks, volcanic eruption, Deep ocean drilling project etc. Discontinuity Indirect- mining activity, meteors, gravitation, magnetic field, and seismic activity. 5-5 10-5 COMPOSITION OF THE EARTH Gutenberg 2900 Discontinuity About 98 per cent of the total crust of the earth is composed of eight elements - oxygen, silicon, aluminium, iron, calcium, sodium, potassium and magnesium. 12-3 Minerals Lehmann 1500 13-3 Discontinuity Minerals are naturally occurring substances that have Inner Core an orderly atomic structure and a definite chemical composition & physical properties. 13-6 6370 z A mineral is composed of two or more elements. But, sometimes single element minerals like sulphur, Mantle copper, silver, gold, graphite etc. are found. z Extends from Moho’s discontinuity to a depth of 2,900 z The basic source of all minerals is hot magma in the km. interior of the earth. Some Major Minerals Granite: batholith generally; Felsic. z Feldspar: half of the earth’s crust is composed of Gabbro: Mafic igneous rocks equivalent to extrusive feldspar; Silicon and Oxygen are common elements of basalt. all types of feldspar; used in ceramic and glass making. Pegmatite & Diorite z Quartz: one of the most important components of 2. Extrusive Igneous Rocks sand and granite; it consists of silica. Feldspar and quartz are the most common minerals found in rocks If the magma reaches the surface and emerges as lava, z Pyroxene: consists of calcium, aluminium, magnesium, it forms extrusive igneous rock. Examples: Basalt, iron and silica; commonly found in meteorites. Andesite, Rhyolite. z Amphibole: Major elements- aluminium, calcium, Classification based on Chemical composition silica, iron, magnesium; used in the asbestos industry. z Those with a high proportion of silica are known as z Mica: comprises potassium, aluminium, magnesium, acidic rocks. iron, silica etc; commonly found in igneous and z Those with a high proportion of basic oxides are metamorphic rocks; used in electrical instruments. denser and darker in appearance are known as basic z Olivine: Major elements- magnesium, iron, and silica; rocks. used in jewellery industry; often found in basaltic rocks. Metallic minerals contain metal content z Felsic Rocks and Mafic Rocks z Precious metals: gold, silver, platinum, etc. Felsic rocks are rich in silicon, oxygen, aluminium, z Ferrous metals: iron and other metals often mixed sodium, and potassium. with iron to form various kinds of steel. Mafic rocks are rich in magnesium and iron. z Non-ferrous metals: include metals like copper, lead, If the rock is highly dominated by Magnesium and zinc, tin, aluminium etc Iron, it is called Ultramafic. Non Metallic minerals: do not contain metal content. 2. Sedimentary Rocks z Eg: Sulphur, phosphates and nitrates. Cement is a mixture of non-metallic minerals. Result of deposition of fragments of rocks by exogenous processes. These deposits through compaction turn into Rocks rocks and this process is called Lithification. Rocks are aggregates of one or more minerals that do not z Mechanically formed- sandstone, conglomerate, have definite chemical composition.. They may be hard or shale, and, loess. soft in varied colours. Petrology is the science of rocks. z Organically formed- geyserite, chalk, limestone, Types of Rocks and, coal. z Chemically formed - dolomite, rock salt, chert, 1. Igneous Rocks halite, and potash. They are solidified from magma and lava. Examples: Granite, gabbro, pegmatite, basalt, volcanic breccia and tuff. Features of Sedimentary Rocks z If molten material is cooled slowly at great depths z Consist of layers and contain fossils (intrusive igneous rocks), mineral grains may be z Most of the sedimentary rocks are permeable and very large (Granite). Sudden cooling at the surface porous (extrusive igneous rocks) results in small grains (Basalt). Intermediate conditions of cooling would 3. Metamorphic Rocks result in intermediate sizes of grains. Formed out of existing rocks that undergo recrystal- Features of Igneous Rocks lisation. Metamorphic rocks are classified into two major z They are hard, granular and crystalline. groups — foliated rocks and nonfoliated rocks. Example: z Do not contain fossils. Gneiss, slate, schist, marble, quartzite etc. z Do not allow water to percolate through them. z Foliated metamorphic rocks: such as gneiss, phyllite, z Less affected by chemical weathering. schist and slate which have a layered or banded z No layers like sedimentary rocks. appearance that is produced by exposure to heat and Classification based on Location of Magma Solidification directed pressure. 1. Intrusive Igneous Rocks z Non-foliated metamorphic rocks: such as marble It is formed by the solidification of magma below the and quartzite which do not have a layered or banded Earth’s surface. Examples: appearance. 6 Interior of The Earth z Metamorphism is a process by which already Earthquake Waves consolidated rocks undergo recrystallisation and reorganisation of materials within the original rocks. Types of Earthquake Waves z Mechanical disruption and reorganisation of the z Body Waves: Emanate from the focus and traverse original minerals within rocks due to breaking through the earth; travel only through the interior and crushing without any appreciable chemical of the earth. They are of two types- Primary Waves changes is called dynamic metamorphism. (P-waves) and Secondary Waves (S-waves) z The materials of rocks chemically alter and z Surface Waves: Originate from the interaction recrystallise due to thermal metamorphism. of body waves with the surface; move along the z Contact metamorphism: Rocks come in contact earth’s surface; recorded last of all the waves on with hot intruding magma and lava and the rock on the seismograph; more destructive. They are of 2 materials recrystallise under high temperatures types- Love waves (L-waves) and Rayleigh Waves z Regional metamorphism: Rocks undergo (R-waves). recrystallisation due to deformation caused by tectonic shearing together with high temperature P Wave Compression S Wave or pressure or both. Surface Waves Body Waves z In the process of metamorphism in some rocks grains or minerals get arranged in layers or direction of propagation dilation lines. Such an arrangement of minerals or grains in metamorphic rocks is called foliation or lineation. Rayleigh Wave Love Wave z Sometimes minerals or materials of different groups are arranged into alternating thin to thick layers, appearing in light and dark shades. Such a structure in metamorphic rocks is called banding. Rocks direction of propagation direction of propagation displaying banding are called banded rocks. Speed of different waves: Primary Waves > Secondary Features of Metamorphic Rocks Waves > Love Waves > Rayleigh Waves. Formed due to pressure and temperature. Very smooth in texture & consists of layers Mediums sometimes. Type of Shadow Wave Motion Speed Travelled Wave Zone Exhibit a wide range of colours. Through Rarely contain fossils. P-Waves Body wave, Faster Solid, Yes, Original Rock Metamorphic Rock Longitudinal than Liquid, between (particle S-waves Gas 105° and Granite Gneiss vibrates 145° Basalt Hornblend parallel to from the wave epicentre Limestone Marble direction) Coal Graphite S-Waves Body wave, Slower Solid Yes, Sandstone Quartzite Transverse than beyond (particle P-waves 105° Shale Slate vibrates from the perpendicular epicenter EARTHQUAKES to the wave direction) An earthquake is the shaking of the earth triggered by the release of energy which creates waves radiating in Love Surface wave, Faster Solid NA all directions. All natural earthquakes arise within the (L-Waves) Transverse than lithosphere, i.e., up to a depth of 200 km from the earth’s Rayleigh surface. waves Rayleigh Surface Slower Solid NA Focus/Hypocentre: Point inside the earth where the (R-Waves) waves, Both than (faster), earthquake originates. Transverse & Love Liquid Epicentre: Point on the earth’s surface directly above the Longitudinal waves (slower) focus. It’s the point that feels the earthquake waves first. Interior of The Earth 7 Shadow Zone z Reservoir-induced Earthquakes: Triggered by the weight of water in large dams. E.g., Reservoir induced P-wave shadow zone seismicity near Koyna Dam (Maharashtra) Distribution of Earthquakes z Mid oceanic ridges (Eg: Atlantic ocean); Alpine- 15 Himalayan system and the Pacific Ocean Ring of Fire. 0° z Earthquakes in mid-oceanic ridge areas are shallow, while those along the Alpine-Himalayan belt and Core Pacific rim are deep-seated. VOLCANOES AND VOLCANIC LANDFORMS 105° 105° A volcano is a geological feature from which molten rock material, gases, ash, and other debris escape to the Earth’s surface. z Asthenosphere is the source from which molten 145° 145° rock materials or magma arise. S-wave shadow zone z When magma moves towards or breaks through the Earth’s crust, it is termed lava. z Materials accompanying eruptions are lava flows, pyroclastic debris, volcanic bombs, ash, dust and gases like nitrogen and sulphur compounds, and smaller quantities of chlorine, hydrogen, and argon. Magma types based on silica content: Increasing silica content implies a lower temperature, explosive eruption Core behaviour and increasing viscosity of magma. 105° 105° 1. Felsic Lava: High silica (65-70%) content, explosive & viscous. 2. Intermediate Lava: 52-63% silica content & less viscous. 3. Mafic Magma: Low silica (45-52%) content, fluid and non-explosive. Ultramafic Lava ( mean) and negative anomaly (e.g., Mt. Everest, temp < mean). Factors Controlling Temperature Distribution z Latitude It has direct control on temperature as the insolation is inversely proportional to the latitude. z Altitude: Higher the altitude, lower is the temperature. Albedo effect reduces temperatures (Decreasing TEMPERATURE z Order of the Albedo: Fresh Snow (0.80) > Ocean ice z Temperature is the measurement in degrees of how > Sand > Green gross > Soil > Forest > Open ocean hot (or cold) a thing (or a place) is. (0.06) > Charcoal (0.04)) z Isotherms are lines connecting places with equal z Distance from the sea: The places situated near the temperatures. Isotherms shift with the apparent sea come under the moderating influence of the sea movement of the sun across the equator. and land breezes Solar Radiation, Heat Balance and Temperature 29 z Air-mass circulation and ocean currents Temperature Inversion Types Warm air-masses/ocean currents: Higher z Surface Temperature Inversion temperature. Takes place on the layers in contact with the Cold air-masses/cold currents: Low temperature. surface through the process of conduction. z Prevailing Winds: Wind origin and speed affect Fog formation is possible if the temperature of temperature distribution. surface air drops below its dew point. z Aspect of Slope: Orientation of slopes influences sunlight exposure, affecting temperature. Common in the higher latitudes; In lower & z Day-Night Cycle: Rotation-induced temperature middle latitudes it occurs during cold nights and variations. gets destroyed during the daytime. z Urban Heat Island (UHI) Effect: Human activities z Valley Inversion elevate temperatures in urban areas. Takes place in hills and mountains due to air drainage. Temperature Inversion Cold air (heavy and dense) produced during the It is a reversal of the normal behaviour of night, flows under the influence of gravity and temperature (temperature drops as altitude increases) in the troposphere, in which a layer of cool air at the moves down the slope to pile up in valley bottoms surface is overlain by a layer of warmer air. with warm air above. This is called air drainage. z Ideal conditions for temperature inversion Protects plants from frost damages Long winter night (outgoing radiation is greater z Frontal Inversion (Advectional type) than the incoming radiation); Occurs when a cold air mass undercuts a warm Clear and cloudless sky; air mass and lifts it aloft. Still air (no/slow horizontal movement of air) It is unstable and is destroyed as the weather which avoids mixing of air; changes. Dry air near the ground surface In polar regions, temperature inversion is normal Consequences of Temperature Inversion throughout the year. z Fog Formation: Warm air sits above cold air which z Effects of Surface Temperature Inversion causes fog by cooling the warm air from below; The lower atmosphere becomes stable; causing Hazardous in polluted areas, limits the diffusion of smoke, dust, and other particles to get trapped air pollutants that aid Fog or Smog formation beneath the inversion layer, leading to formation z Frost Impact: When warm air condenses at freezing of dense fog. temperatures due to cooling by cold air below; In hilly and mountainous terrains, inversion is Damages crops and orchards. due to a process called air drainage (downward flow of cold air from mountain slopes to valleys z Atmospheric Stability: Restricts vertical air during night). It acts as a protective shield for movement that discourages rainfall and promotes dry plants, saving them from frost damage. conditions and aridity. v v v 30 Solar Radiation, Heat Balance and Temperature Atmospheric Circulation and 8 Weather Systems Atmospheric pressure is the weight of a column of air Forces Affecting the Velocity and Direction contained in a unit area. It decreases with height; rate of of Wind decrease is roughly 1 millibar/10 metres. z Pressure Gradient Force from high pressure to Wind is the horizontal movement of air that flows from low pressure; closely spaced isobars indicate strong high pressure to low pressure areas. pressure gradients and hence stronger winds. Air current is the vertical or nearly vertical movement z Frictional Force: affects the speed of the wind due to of air. Earth’s surface irregularities; greatest at the surface and minimal over the sea surface and generally Distribution of Air Pressure extends up to an elevation of 1 - 3 km. It is not uniform and varies both vertically and horizontally z Coriolis Force: The rotation of the earth about its on the Earth’s surface. Lower layers have a higher density axis produces a pseudo force affecting the direction and exert more pressure. of the wind; deflects the wind to the right direction in the northern hemisphere and to the left in the Vertical Variation southern hemisphere (Buy Ballot Law), which z Decreases with an increase in altitude in the lower depends on the wind velocity; atmosphere but not at the same rate due to variations It is directly proportional to the angle of in air density controlling factors such as temperature, latitude; maximum at the poles and is absent water vapour and gravity. at the equator (thus cyclones are not formed at z The vertical pressure gradient force is much larger the equator) than that of the horizontal pressure gradient. Acts perpendicular to the pressure gradient force creating cyclonic conditions, higher the Pressure gradient is the ratio between the pressure pressure gradient force, higher the velocity of difference and the actual horizontal distance between two points. the wind and the larger is the deflection of the wind. z A rising pressure indicates stable weather whereas a falling pressure indicates cloudy and unstable GENERAL CIRCULATION OF weather. THE ATMOSPHERE Horizontal Variation Pattern of movement of the planetary winds also sets z Studied by drawing isobars (line connecting points in motion the ocean water circulation and they together that have equal values of pressure). influence the earth’s climate. The pattern of planetary z Close spacing of isobars expresses a steep pressure winds largely depends on: gradient. z Latitudinal variation of atmospheric heating. z Emergence of pressure belts. Factors Responsible for Variation z The migration of belts follows the apparent path of z High temperatures lead to rise of air, hence low the sun. pressure and vice versa. z The distribution of continents and oceans. z The Earth’s rotation leads to rise of air at equator z The rotation of the earth. and fall in tropics; hence, equator has low pressure while tropics have high pressure. Global Pressure Belts z Air with a higher quantity of water vapour has The horizontal distribution of air pressure across the lower pressure. latitudes is characterised by high or low pressure belts. Equatorial Low Pressure Belt z Winds blow out of this region towards the equator: Zone of wind convergence along the equator and within North East trade winds (Northern Hemisphere) and 5 degrees north and south; this belt has Doldrums. South East trade winds (Southern Hemisphere). These winds bring rainfall to the east and aridity Doldrums (zone of calm air) due to virtual absence of (Deserts) to the west coast of continents within the surface winds at 0° Latitude. tropics. z Thermally induced pressure belt as it is formed z Winds blow out of this region towards the Temperate because of the differential heating of the earth. low-pressure belt: South Westerlies (Northern z Due to the overhead sun throughout the year, the Hemisphere) and North Westerlies (Southern air gets warm and rises over the equatorial region, Hemisphere). These carry warm equatorial waters producing equatorial low pressure. and to western coasts of temperate lands. [UPSC z Only conventional currents are present, horizontal 2015] movement of air is absent due to excessive heating. z In the southern hemisphere Westerlies are referred z Zone of convergence of trade winds from two to as Roaring Forties, Furious Fifties; and Shrieking hemispheres from subtropical high pressure belts. or Stormy Sixties according to their speed at different z Vertical winds (convection) carry moisture to latitudes. cumulonimbus clouds and lead to thunderstorms (convectional rainfall). Sub Polar Low-Pressure Belts Zone of wind convergence towards the pole along 60° N z It is also known as Inter Tropical Convergence and 60° S latitudes. Zone (ITCZ) or Thermal Equator because the winds flowing from sub-tropical high-pressure belts z Dynamically induced pressure belt as it is formed converge here. because of the rotation of the earth. z Winds coming from the subtropical and the polar high Intertropical Convergence Zone (ITCZ) belts converge here to produce cyclonic storms or Low pressure forms due to air convection driven by low-pressure conditions. This zone of convergence intense sunlight; Winds from the tropics converge is also known as the polar front. into this low-pressure area, ascend within the convective cell, reach the troposphere’s upper limit Polar High Pressure Belt (approximately 14 km), and subsequently travel Close to the poles between 80° – 90° N and S latitudes poleward, accumulating around 30°N and 30°S latitudes. z Thermally induced pressure belt as it is formed because of the differential heating of the earth. z The position of the belt varies with the apparent z In Polar Regions, Sun Rays are always slanting, movement of the Sun. resulting in low temperatures. z ‘Zero’ Coriolis force, so no cyclones at the equator. z Because of low temperature, air compresses and its Subtropical High-Pressure Belt density increases. Hence, high pressure is found here. Zone of wind divergence along 30° N and 30° S latitude. z Winds from these belts blow towards the subpolar z Dynamically induced pressure belt as it is formed low pressure belt. because of the rotation of the earth. z Uprising air of the equatorial region moves towards the poles and gets deflected due to the earth’s rotation. After becoming cold and heavy, it descends at these high-pressure belts. z The corresponding latitudes of sub-tropical high pressure are called Horse latitudes due to calm weather conditions and absence of strong winds. z Subsiding air is warm and dry; therefore, most of the deserts are present along this belt, in both hemispheres. Cold ocean current increases the aridity of these deserts on the western margin of continents. 32 Atmospheric Circulation and Weather Systems Pressure Cells GEOSTROPHIC WINDS The wind belts girdling the planet are organised into They are the winds of upper atmosphere, 2 - 3 km three cells in each hemisphere. above the surface, that are free from frictional effect of the surface and are controlled mainly by the pressure Hadley Cell gradient and the Coriolis force. z Warm air at the ITCZ rises, creating a low pressure z They flow parallel to the isobars because of the zone and winds from the tropics blow towards this balancing of the Pressure Gradient Force by the equatorial low pressure zone. Coriolis force in the upper troposphere. z The converged air rises and moves towards the poles. z These winds can also form in a cyclonic or anticyclonic This causes accumulation of air at about 30° N and S. circulation. z This air gets cooled and sinks to ground and forms a z It is also the reason why the air rising from the Subtropical High. equatorial belt does not go straight towards the pole but descends in the subtropics. z Again this sinked air flows towards equatorial low z Gradient Wind: Considers airflow along a curved from the Subtropical High as Easterlies. path, extending the concept of geostrophic wind Ferrel Cell moving along straight and parallel isobars. z Circulation of air with sinking air at Subtropical z One important type o

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