Geomorphology Notes PDF

 GS-1 (Geography) UNIVERSE.....................................................................................................................

 GS-1 (Geography) UNIVERSE.................................................................................................................................................................2 GALAXIES................................................................................................................................................................. 5 STARS.......................................................................................................................................................................5 SOLAR SYSTEM........................................................................................................................................................ 7 THE SUN.................................................................................................................................................................. 8 PLANETS................................................................................................................................................................ 10 EVOLUTION OF EARTH.......................................................................................................................................... 11 EARTH FACTS:........................................................................................................................................................ 12 MILANKOVITCH CYCLES........................................................................................................................................ 12 MOON.....................................................................................................................................................................13 ECLIPSES:.............................................................................................................................................................. 14 PYQ.........................................................................................................................................................................15 INTERIOR OF THE EARTH...................................................................................................................................... 18 EARTHQUAKES...................................................................................................................................................... 20 EARTH MOVEMENTS..............................................................................................................................................25 CONTINENTAL DRIFT & SEA FLOOR SPREAD THEORIES......................................................................................29 PLATE TECTONICS THEORY.................................................................................................................................. 32 VOLCANISM............................................................................................................................................................35 OROGENY...............................................................................................................................................................41 ROCKS & ROCK CYCLE...........................................................................................................................................43 CYCLES OF EROSION............................................................................................................................................. 46 “All material appearing on the “Sarrthi IAS” ("content") is protected by © copyright. You may not copy, reproduce, distribute, publish, display, perform, modify, create derivative works, transmit, or in any way exploit any such content” ©Sarrthi IAS 9569093856 www.sarrthiias.com 1  GS-1 (Geography) UNIVERSE Gaseous Hypothesis: Given by Kant Large particles of primordial matter were scattered in the universe. They started colliding against each other due to gravitational attraction. Collision resulted in the generation of heat. Heat changed the primordial matter from solid to liquid and from liquid to gaseous state, creating a nebula. Nebula started rotating around its axis, creating a bulge in the center of the gaseous mass. When this bulge increased in size, the rings started forming one by one and were separated from the middle part of the nebula. Residual central mass became the sun and the rest of the rings became the planets. How did the moons form? ○ Repetition of the same process at the planet level. ○ Rings were separated from the newly formed planets. ○ Material of each ring condensed to form satellites of the concerned planets. Drawback: ○ Not explained the source of the primordial matter. ○ Not explained the source of energy which caused the collision of primordial particles. ○ According to the science of the law of motion, the collision of particles doesn’t generate rotatory motion. Nebular Hypothesis: 1796. By Laplace Modified version of Kant’s theory Assumptions: ○ A huge and hot gaseous nebula is present in the space. Thus, he solved the problem of heat of the nebula through this assumption. ○ From the very beginning, a huge and hot nebula was rotating (spinning) on its axis. ©Sarrthi IAS 9569093856 www.sarrthiias.com 2  GS-1 (Geography) ○ A huge and hot gaseous matter called a nebula existed in space which was continuously rotating on its axis. ○ Nebula was losing heat from its outer surface due to the process of radiation and was thus reducing in size and volume due to contraction. ○ As its size reduced, its velocity of rotatory motion began to increase. With increased velocity, the rings started detaching. Each ring condensed at a point in the form of a gaseous mass which started rotating around the nebula. Gaseous mass later cooled and formed the planets. The remaining part of the nebula thus became the sun. Limitations: ○ Did not explain the source of origin of the nebula. ○ If the planets have been formed from the rotating nebula, then the residual part of the nebula i.e., the Sun should rotate at the highest speed due to the decrease in its size, but it is not so. Chamberlin–Moulton planetesimal hypothesis According to this hypothesis, a star passed close to the young Sun, causing tidal bulges and solar prominences that led to repeated ejections of material from the Sun. Gravitational effects from the passing star created spiral arms of ejected material, with some of it remaining in orbit. This material cooled and condensed into small bodies called planetesimals and larger protoplanets. Over time, collisions among these objects formed the planets and their moons, with comets and asteroids as leftover debris. Accretion Model By Otto Schmidt (1944) and Viktor Safronov (1969). Constant accretion of particles convert them from a nebula to planets eventually. Nebula 🡪 Dust grains 🡪 Boulders 🡪 Planetesimals 🡪 Planets ©Sarrthi IAS 9569093856 www.sarrthiias.com 3  GS-1 (Geography) Big Bang Hypothesis: Georges Lemaitre proposed in 1920s. He theorized that the universe began from a single primordial atom. The idea received major boosts from Edwin Hubble's observations that galaxies are speeding away from us in all directions, as well as from the 1960s discovery of cosmic microwave radiation—interpreted as echoes of the big bang—by Arno Penzias and Robert Wilson. Theory was finally validated in 1972. All matter in the universe existed in the form of dense and huge primordial matter. A violent explosion took place in this primordial matter. Due to this, the dust particles present in this matter were scattered in the universe. Over several million years, slightly denser regions become gravitationally attracted to each other. They grew even denser, forming gas clouds, stars, galaxies, and other astronomical structures. PROOF: Hubble’s Law (Hubble-Lemaitre law): galaxies farther away from us are moving away at faster speeds, indicating the expansion of the universe. ○ Basis of Hubble’s law is redshift, which is the elongation of light waves to longer wavelengths, often toward the red end of the spectrum, caused by an object moving away from the observer, commonly observed in distant galaxies due to the expansion of the universe. Cosmic Microwave Background Emissions: ○ Discovered by American physicists Arno Penzias and Robert Wilson, who detected it in 1965. ○ It is the faint glow of electromagnetic radiation that fills the universe. It is the oldest light in the universe, dating back to about 380,000 years after the Big Bang. It is essentially the afterglow of the hot, dense state of the early universe, when photons decoupled from matter and began to travel freely through space. ○ It also confirms the Big bang theory. ©Sarrthi IAS 9569093856 www.sarrthiias.com 4  GS-1 (Geography) GALAXIES Formation ○ After the Big Bang (13.8 billion years ago): Initial fluctuations in the density of matter. The role of Dark matter’s gravity is considered here. ○ First Galaxies (about 1 billion years post-Big Bang): Gas clouds collapse under gravity, forming the first stars and galaxies. ○ Galaxy Evolution (1 billion years to present): Galaxies grow and evolve through mergers and interactions. Types of Galaxies ○ Elliptical Galaxies: Spherical or oval-shaped with little gas and dust; older, redder stars dominate. ○ Spiral Galaxies: Flat, disk-shaped with spiral arms; contain young, blue stars and significant gas and dust (e.g., Milky Way). ○ Irregular Galaxies: No defined shape, often rich in gas and dust, leading to star formation. ○ Peculiar Galaxies: Unusual shapes or features due to interactions or mergers with other galaxies. Active Galactic Nuclei: highly energetic regions at the centers of some galaxies, powered by supermassive black holes accreting matter. These regions emit enormous amounts of radiation across the electromagnetic spectrum and are categorized based on their observational characteristics. Types of AGN: ○ Seyfert Galaxies: Spiral galaxies with extremely bright cores. Strong emissions in the infrared and optical wavelengths. ○ Blazars: AGN with jets oriented toward Earth. Highly variable and intense emissions across the electromagnetic spectrum, including gamma rays; are notable for rapid brightness changes and polarization. ○ Quasars: The most luminous type of AGN, visible across vast distances. Emit massive amounts of energy, primarily in light and radio waves; were more common in the early universe. STARS Their formation after the Big Bang: ○ Big Bang (13.8 billion years ago): The universe begins with a hot, dense state. ○ Formation of Hydrogen and Helium: As the universe expands and cools, protons and neutrons form hydrogen and helium. ○ Cosmic Microwave Background (CMB): Approximately 380,000 years post-Big Bang, the universe cools enough for electrons to combine with protons and form neutral atoms, releasing the CMB. ○ Formation of Gas Clouds (100 million to 200 million years post-Big Bang): Gravity causes hydrogen and helium gas to clump together, forming large clouds. ○ Protostar Formation (200 million to 400 million years post-Big Bang): These gas clouds collapse under gravity, increasing temperature and pressure, forming protostars. ○ Nuclear Fusion Ignition (200 million to 400 million years post-Big Bang): When core temperatures are high enough, nuclear fusion ignites, and stars are born. Lifecycle of stars: ○ Stellar Nebula: Stars form from collapsing clouds of gas and dust. ○ Protostar: As the nebula collapses, a protostar forms and heats up. ○ Main Sequence: Star enters a stable phase, fusing hydrogen into helium. Low-Mass Stars (mass < 8 times that of Sun): Red Giant: Exhausts hydrogen, expands, and cools. Planetary Nebula: Outer layers shed. White Dwarf: Core remains, cools over time. It may convert into a black dwarf over time, but we do not have any solid proof of this as of now. High-Mass Stars (mass > 8 times that of the sun): Red Supergiant: Similar process but on a larger scale. Supernova: Catastrophic explosion after iron buildup in core. ©Sarrthi IAS 9569093856 www.sarrthiias.com 5  GS-1 (Geography) Neutron Star/Black Hole: The remnant core collapses into a neutron star or black hole, depending on mass. Chandrashekhar Limit: If after the shedding of the outer layers, due to supernova, or without it, the mass of the remaining core is less than 1.44 times that of the sun, we get a white dwarf. Otherwise, we get a neutron star (1.44-3) or a black hole (>3). Population 3, 2 and 1 stars Stars are classified into populations based on their metallicity, which refers to the abundance of elements heavier than hydrogen and helium. Population III Stars (Hypothetical): These are theorized to be the very first stars born in the universe, hundreds of millions of years after the Big Bang. ○ Extremely Metal-Poor: They are believed to have been almost entirely composed of hydrogen and helium, with virtually no heavier elements because those elements hadn't been forged in abundance yet. ○ Massive and Short-Lived: Due to their large size, they are thought to have been incredibly massive and short-lived, burning out rapidly in a few million years. ○ Direct evidence for their existence has not yet been found. ○ Do not have a planetary system. Population II Stars (Oldest Observed; 5-10 bya): These are the oldest stars still observable in the Milky Way galaxy. ○ Metal-Poor: They contain very little of the heavier elements compared to younger stars. ○ Location: Population II stars are typically found in the galactic halo (spherical region surrounding the disk) and globular clusters (dense collections of millions of old stars). ○ Slower Evolution: Due to their lower metallicity, they evolve more slowly and have longer lifespans than stars with higher metal content. Population I Stars (Younger and Richer in Metals; 4-5 bya): These are the younger stars, including our Sun. ○ Metal-Rich: They contain a higher proportion of heavier elements compared to Population II stars. This enrichment is due to previous generations of stars that lived, died, and scattered these elements into the interstellar medium. ○ Location: Population I stars are found in the galactic disk (flattened disc where most stars and gas reside) and spiral arms of the Milky Way. ○ Faster Evolution: Their higher metallicity can lead to faster stellar evolution and shorter lifespans compared to Population II stars. Neutron Stars Neutron stars are extremely dense stellar remnants formed from the collapsed core of massive stars (about 8-25 times the mass of the Sun) after a supernova explosion. They are composed almost entirely of neutrons and have incredibly strong gravitational and magnetic fields. Pulsars: Rapidly rotating neutron stars that emit beams of electromagnetic radiation from their magnetic poles, observed as regular pulses. Black Holes Black holes are regions of spacetime with gravitational pull so strong that nothing, not even light, can escape from them. They form from the remnants of massive stars (more than 25 times the mass of the Sun) after they undergo a supernova explosion and collapse under their own gravity. ©Sarrthi IAS 9569093856 www.sarrthiias.com 6  GS-1 (Geography) Event Horizon: The boundary around a black hole beyond which nothing can escape. Accretion Disks: Disks of gas and dust spiraling into black holes, emitting intense radiation due to friction and heating. Gravitational Waves: Ripples in spacetime produced by the acceleration of massive objects like merging black holes, detectable by observatories like LIGO and Virgo. Spaghettification: Spaghettification is the process where objects are stretched and torn apart by intense tidal forces as they approach a black hole. Hawking Radiation: Hawking radiation is the theoretical emission of particles from black holes due to quantum effects near the event horizon, leading to gradual black hole evaporation. SOLAR SYSTEM Components of the Solar System The Sun: The central star of the solar system, a massive ball of hydrogen and helium undergoing nuclear fusion. Planets: Major celestial bodies orbiting the Sun, classified as terrestrial (Mercury, Venus, Earth, Mars) and gas giants (Jupiter, Saturn) or ice giants (Uranus, Neptune). Dwarf Planets: Celestial bodies orbiting the Sun that are spherical but have not cleared their orbital path. The solar system has 5 known dwarf planets: Pluto, Ceres (the biggest), Eris, Haumea, and Makemake (the newest). What is the criteria for calling a body dwarf planet? ○ In orbit around the Sun: The object must be gravitationally bound to the Sun and travel in an orbit around it. ○ Massive enough for hydrostatic equilibrium (nearly round shape): The object's own gravity must be strong enough to pull it into a roughly round shape, overcoming the forces of its rigid body. This is in contrast to asteroids, which are irregularly shaped due to their weaker gravity. ○ Not a satellite (moon) of another object: The object cannot be gravitationally bound to another planet or large object and act as its moon. ○ Has not cleared the neighborhood around its orbit: This is the key distinction between a dwarf planet and a full-fledged planet. The object's gravity must not be strong enough to have cleared the path around its orbit of other objects of comparable size. Moons: Natural satellites orbiting planets and dwarf planets. According to NASA, the current tally of total moons in the solar system is 293 (1 for Earth; 2 for Mars; 95 at Jupiter; 146 at Saturn; 28 at Uranus; 16 at Neptune; and five for dwarf planet Pluto.) Asteroids: Small rocky bodies, primarily found in the asteroid belt between Mars and Jupiter. Comets: Icy bodies that release gas and dust, forming a glowing coma and tail when near the Sun, originating from the Kuiper Belt or Oort Cloud. Meteoroids: Small particles from comets or asteroids that travel through space. Meteor: When a meteoroid enters Earth's atmosphere, it heats up due to friction with air molecules. This burning object, streaking across the sky, is what we call a meteor, commonly known as a "shooting star." Most meteors are completely vaporized by the heat before reaching the ground. Meteorite: If a meteoroid is large and sturdy enough to survive its fiery passage through the atmosphere and impact Earth's surface, it becomes a meteorite. Meteorites can be of various sizes, from a pebble to a massive rock. Kuiper Belt: A region beyond Neptune filled with icy bodies and dwarf planets. Oort Cloud: A distant spherical shell of icy objects surrounding the solar system, believed to be the source of long-period comets. Heliosphere: The bubble of solar wind surrounding the solar system. Termination Shock: Where the solar wind slows from supersonic to subsonic speeds. This slowing down is due to the solar wind particles encountering the denser interstellar medium's pressure. Heliosheath: The turbulent region beyond the termination shock. In this region, the solar wind's velocity decreases further, and the magnetic field becomes more irregular. The heliosheath acts as the outer layer of the heliosphere and is a turbulent region where the solar wind's influence weakens. ©Sarrthi IAS 9569093856 www.sarrthiias.com 7  GS-1 (Geography) Heliopause: The boundary where solar wind pressure balances with interstellar pressure. It marks the outer edge of the heliosphere. Beyond the heliopause, the interstellar medium predominates, and the influence of the solar wind ceases. The heliopause is considered the final frontier of the solar wind's reach, marking the transition between the heliosphere and interstellar space. Bow Shock: The shockwave formed as the heliosphere moves through the interstellar medium. It is analogous to the shock wave that forms in front of a moving boat or a supersonic aircraft. As the heliosphere plows through the interstellar medium, it creates this shockwave, where the interstellar medium is abruptly heated and slowed down due to the presence of the heliosphere. However, the existence of such a region has been contested by the data received from the Voyager 1 and 2 missions by NASA. THE SUN Composition: 92% hydrogen 8% helium Interior: ○ Core: Nuclear fusion takes place here. The temperature here is over 15 million degrees C. ○ Radiative Zone: Region in which energy transfer is through thermal radiation instead of convection. (Radiation: emission or transmission of energy in the form of electromagnetic waves or particles.) ○ Convective Zone: The convection cells move in this zone for energy transportation. (Convection: transfer of heat through the movement of a fluid (such as air or water) caused by differences in temperature and density.) The Sun is made up of hot gases, so it lacks any "surface" like earth. Instead, as we move from the Sun’s outer atmosphere toward the Sun's core, the gas gets denser and denser. Atmosphere: ○ Photosphere: Sun’s outer atmosphere is transparent, but when we try to look through the atmosphere deeper into the Sun, our view is blocked. The photosphere is the layer that begins where the Sun starts to look opaque. ○ Chromosphere: layer above the photosphere. Outer chromosphere is about 10,000 degrees C. ○ Corona: Layer of hot plasma which extends millions of kilometers into the space from the surface of the chromosphere and has an irregular shape. Coronal Mass Ejection: ○ Large expulsions of plasma and magnetic field from the Sun’s corona. ○ 15-18 hours to reach Earth. Can be slower. ○ Expand as they move away from the sun. Solar flares: ○ Tremendous explosions due to the release of energy in twisted magnetic fields (Like when rubber bands come back to their original size.) ○ It causes a sudden flash of increased brightness on the Sun. ○ Can be, but not always, associated with CMEs. ©Sarrthi IAS 9569093856 www.sarrthiias.com 8  GS-1 (Geography) ○ Flares are categorized according to their strength. The smallest ones are B-class, followed by C, M and X, the largest. Solar Winds: ○ Solar wind is a stream of charged particles released from the upper atmosphere of the Sun (Corona). ○ Solar wind is created by the outward expansion of plasma. ○ Plasma is continually heated to the point that the Sun's gravity can't hold it down. Auroras: ○ Aurora (polar light) is a natural phenomenon which is characterised by a display of lights in the Polar region skies. ○ Solar wind has charged protons and electrons that excite atmospheric Oxygen and Nitrogen. ○ When Oxygen and Nitrogen return from excited states to the ground state, they release Photons, which are displayed as the Aurora lights. ○ Northern Hemisphere: Aurora Borealis ○ Southern Hemisphere: Aurora Australis ○ Why are auroras only on the poles? Earth is a magnet. Currently, the North and the South Poles of this magnet are near our geographical North and South Poles. The charged particles get attracted towards the magnetic Poles. This causes auroras at the geographical north and south poles. Van Allen Radiation Belt: The Van Allen radiation belts consist of charged particles trapped by Earth's magnetic field, forming doughnut-shaped regions around the planet. They protect Earth from solar radiation but can pose risks to spacecraft passing through them. ○ The inner and outer radiation belts are two distinct regions within the Van Allen radiation belts surrounding Earth. The inner belt is composed mainly of protons and extends from about 1,000 ©Sarrthi IAS 9569093856 www.sarrthiias.com 9  GS-1 (Geography) to 6,000 kilometers above the Earth's surface, while the outer belt consists mostly of electrons and extends from about 13,000 to 60,000 kilometers above the surface. Sunspots: darker (cooler) areas on the solar surface. Solar Maxima & Solar Minima: ○ Solar minima and maxima are the two extremes of the Sun's 11-year and 400-year activity cycles. ○ Solar maximum: During this period, the highest solar activity is observed. The Sun has many sunspots and eruptions of solar flares. ○ Solar minimum is the period of least solar activity in the 11-year solar cycle. Goldilocks Zone: ○ Distance from the star where a planet’s atmospheric conditions are such that water remains liquid. ○ Distance from the star where the Goldilocks zone exists depends on the size and the strength of the star. ○ E.g. Earth; Kepler-186f. PLANETS Feature Inner Planets Outer Planets Number 4 (Mercury, Venus, Earth, Mars) 4 (Jupiter, Saturn, Uranus, Neptune) Primarily gaseous (hydrogen, helium) Composition Primarily rocky (iron, silicon) with some icy components Size Smaller diameter and mass Significantly larger diameter and mass Density Higher density Lower density Solid surfaces with craters, No solid surface; thick atmosphere Surface volcanoes, and canyons (except composed mostly of hydrogen and Venus which has a thick atmosphere) helium Weaker magnetic fields (except Magnetic Field Strong magnetic fields Earth) Most have rings composed of dust and Rings No rings ice particles (Jupiter: 1, Saturn: 2, Uranus: 2, Neptune: 6) Many moons (Jupiter: 95, Saturn: 146, Moons Fewer moons (Earth: 1, Mars: 2) Uranus: 28, Neptune: 14) Wider range of temperatures, with Colder temperatures due to distance Temperature hot days and cold nights (except from the Sun Venus with a constant hot surface) ©Sarrthi IAS 9569093856 www.sarrthiias.com 10  GS-1 (Geography) Closer to the Sun, formed from Farther from the Sun, formed from Formation denser material in the early solar leftover icy material and gases system Shorter orbital periods (Mercury: 88 Longer orbital periods (Jupiter: 12 Orbit days, Earth: 365 days, Mars: 687 years, Saturn: 29 years, Uranus: 84 days) years, Neptune: 165 years) Venus and Uranus rotate from East to West. The Axis of Uranus is parallel to its orbit. The Giant and the Little red spots are a defining feature of Jupiter. They are huge storms. The former is 16000 km in diameter while the latter is 3500 km in diameter. Atmosphere of different Planets: ○ Mercury: Very thin, most of it is lost due to solar storms ○ Venus: thick atmosphere, mainly made of CO2, making the planet super-hot due to the greenhouse effect. ○ Mars: Very thin, rich in CO2 ○ Jupiter and Saturn: Hydrogen and Helium with the addition of some sulphurous and carbon gases. ○ Uranus and Neptune: Mainly Methane and Ammonia. EVOLUTION OF EARTH Phases: Crust formation: ○ Light substances floated up from deep inside, and then they changed into hard rocks after cooling. ○ As the earth’s interior continued to cool, it contracted, and the outer crust wrinkled forming ridges and basins. Atmosphere Formation: ○ Degassing: lighter substances swarmed up above the earth’s surface forming an atmosphere of gases. ○ Happened in 3 phases: Early Atmosphere was rich in Hydrogen and Helium. These gases were eventually stripped away by solar wind. Stage 2: The volcanic activities on partially solidified Earth, led to the release of gases like Co2, Nitrogen Oxides, and water vapour. The water vapour released formed clouds and led to the formation of oceans through rainfall. Stage 3: As life evolved on Earth, the configuration of the atmosphere changed, and the concentration of Oxygen started to increase. Ocean Formation: ○ Atmospheric Gases formed the Clouds, which cause heavy rains for thousands of years. ○ This water was collected in basins, forming oceans. ○ Then life started in the ocean. Life on Earth: ©Sarrthi IAS 9569093856 www.sarrthiias.com 11  GS-1 (Geography) ○ 4.5 Billion Years Ago: Earth forms, hot and bombarded by asteroids. ○ Over the next billion years: As Earth cools, conditions become favorable for complex molecules to form in the oceans. ○ Around 3.8 Billion Years Ago: Simple life emerges, possibly near deep-sea vents, utilizing chemicals for energy (not sunlight). These were likely single-celled organisms (blue-green algae) with basic building blocks of life. ○ Proof: Chemical Biogenesis or the Miller-Urey experiment, conducted in 1953 by Stanley Miller and Harold Urey. It proved that in plausible early Earth conditions, organic molecules important for life could arise naturally. Inorganic molecules could convert to organic ones. This can lead to the creation of necessary amino acids, essential for the creation of single-celled organisms that could divide. EARTH FACTS: Titled on Axis: 23.5 degrees from the vertical. (North Star) 1 rotation: 23 hrs 46 mins 4 seconds. Speed of rotation is reducing (due to wind and wave friction). Looking down at the North Pole from space, Earth is rotating in a counterclockwise direction. Revolution in elliptical orbit. 365 days, 5 hours and 48 minutes. Aphelion: Point of the Earth’s orbit that is farthest away from the Sun. Perihelion: Point of the Earth’s orbit that is nearest to the Sun. Latitudes and Longitudes: ○ Imaginary lines created to make it easy to locate places on the Earth. ○ Parallel lines running in east-west directions are latitudes. ○ Lines running North to South and meeting each other at the poles are the longitudes. MILANKOVITCH CYCLES Glaciers have come and gone many times on earth Variation in Earth–Sun relations cause annual insolation variation on earth leading to climate change. Milutin Milankovitch said Earth’s climate is influenced by changes in the Earth–Sun relations in terms of amount and direction of Earth’s axial tilt and Earth’s orbital shape. Such climatic changes are known as the Milankovitch cycles. Eccentricity: ○ Earth’s orbit shape varies on a 100,000-year cycle becoming more elliptical and then more circular. ○ This alters the Earth-Sun distance, therefore altering the amount of solar energy the Earth receives through the annual cycle. ©Sarrthi IAS 9569093856 www.sarrthiias.com 12  GS-1 (Geography) Obliquity/Axial Tilt: ○ Angle at which the Earth’s axis is tilted with respect to the Earth’s orbital plane. ○ Greater inclination means that the seasonal variation between the low latitudes and high latitudes tends to be greater. ○ Variation between 22-24.5 degrees ○ Periodicity: 41,000 years. Precession (wobble): ○ The direction in which the Earth’s axis of rotation is pointed. ○ Precession alters the timing of the seasons relative to Earth’s position in its orbit around the Sun. ○ The orientation of earth's axis varies in the 25,800-year cycle of precession. Collective effects of changes in the Sun-Earth relations on Earth’s climate in geological history plotted on a graph known as the Milankovitch curve. MOON The moon is Earth's only natural satellite. It orbits the Earth at an average distance of 384,400 km. The moon is a bit more than one-fourth (27%) the size of Earth. Its gravity influences Earth's tides. Orbital distance: 384400 km (average). Size: 27% of the Earth. Perigee: The point on the Moon's orbit closest to the Earth. Apogee: The point on the Moon's orbit farthest away from the Earth. Tidally locked to the Earth: ○ This means that the moon always shows one face to the Earth. ○ Earth’s gravitational interaction slowed down moon’s rotation until it became tidally locked. ○ Earlier its rotation duration was only 10 days. ©Sarrthi IAS 9569093856 www.sarrthiias.com 13  GS-1 (Geography) Creation: ○ Fission Theory, George Darwin (1838): The Moon once formed part of the rapidly spinning Earth, which flung off a large chunk due to the centrifugal force, creating the Moon. This explains the Moon's receding path from Earth and Earth's slightly bulging equatorial region. Not accepted anymore. ○ Giant Impact Hypothesis (Big Splash): collision between the proto-Earth and a Mars-sized planet (called Theia), around 4.5 bn years ago created the Moon. ECLIPSES: Lunar Eclipse: Earth between the Sun and the Moon ○ Umbra: darkest region of a shadow ○ Penumbra: region in which only a portion of the light source is blocked by the occluding body. ○ Blood Moon: When the whole of the lunar disc enters the Earthʼs umbra, the Moon appears reddish. ○ Blue Moon: Not related to the eclipses. When we get 2 full moons in a month, the 2nd one is called Blue Moon. Solar Eclipse: Moon Between Earth and the Sun. ○ The moon blocks the light of the sun from reaching the Earth’s surface and casts a shadow (Umbra) on the Earth. ○ Annular Solar Eclipse: When the Moon passes directly between the Earth and the Sun but does not completely cover the Sun's disk, as the Moon is farther away from Earth, making its shadow on Earth smaller. ○ Total Solar Eclipse: When the moon completely covers the sun, as it is closer to the Earth. It also leads to the Diamond ring effect (As the Moon moves across the face of the Sun, a point comes when only a single bright spot of sunlight remains visible, looking much like a shining diamond.) ○ Partial Solar eclipse can be due to 2 reasons: When sun, moon and the earth are not in a straight line, only a penumbra region is formed, causing partial eclipse. ©Sarrthi IAS 9569093856 www.sarrthiias.com 14  GS-1 (Geography) When they are in a straight line, some regions see a full solar eclipse (umbra) while some see a partial one (penumbra). PYQ Q.1) If a major solar storm (solar flare) reaches the Earth, which of the following are the possible effects on the Earth ? (2022) 1. GPS and navigation systems could fail. 2. Tsunamis could occur at equatorial regions. 3. Power grids could be damaged. 4. Intense auroras could occur over much of the Earth. 5. Forest fires could take place over much of the planet. 6. Orbits of the satellites could be disturbed. 7. Shortwave radio communication of the aircraft flying over polar regions could be interrupted. Select the correct answer using the code given below: (a) 1, 2, 4 and 5 only (b) 2, 3, 5, 6 and 7 only (c) 1, 3, 4, 6 and 7 only (d) 1, 2, 3, 4, 5, 6 and 7 Answer - C Explanation: Solar storms can play a havoc on the electrical and electronic systems of the Earth, affecting power systems, satellite communication, nd can cause intense auroras. In May 2024 one such intense solar storm caused the auroras to be seen as far away from the pole as Leh in India. Tsunamis require vertical shift of water which is not caused by the flares. These flare are not related to increased temperature on earth, so they do not cause forest fires. Q.2) The term 'Goldilocks Zone' is often seen in the news in the context of (2015) (a) the limits of habitable zone above the surface of the Earth (b) regions inside the Earth where shale gas is available (c) search for the Earth-like planets in outer space (d) search for meteorites containing precious metals Answer - C Explanation: Goldilocks zone is the distance from the star, where the temperature is such that water can stay in Liquid form. Earth lies in the Goldilocks Zone of the Sun. If we wish to find life form similar to that found on the Earth, then we need to search for the planets lying in the Goldilocks zone of their respective stars. Q.3) What is the difference between asteroids and comets? (2011) 1. Asteroids are small rocky planetoids, while comets are formed of frozen gases held together by a rocky and metallic material. 2. Asteroids are found mostly between the orbits of Jupiter and Mars, while comets are found mostly between Venus and mercury. 3. Comets show a perceptible glowing tail, while asteroids do not. Which of the statements given above is/are correct ? (a) 1 and 2 only (b) 1 and 3 only (c) 3 only ©Sarrthi IAS 9569093856 www.sarrthiias.com 15  GS-1 (Geography) (d) 1, 2 and 3 Answer. B Explanation The main difference between asteroids and comets is their composition, as in, what they are made of Asteroids are made up of metals and rocky material, while comets are made up of ice, dust and rocky material. Both asteroids and comets were formed early in the history of the solar system about 4.5 billion years ago. Asteroids formed much closer to the Sun, where it was too warm for ice to remain solid. Comets formed farther from the Sun where ice would not melt. Comets which approach the Sun lose material with each orbit because some of their ice melts and evaporates to form a tail. Asteroids are a series of very small planets or fragments of planets lying between the orbits of Mars and Jupiter. They revolve around the Sun in the same way as planets, unlike comets. Q.4) Which one of the following sets of elements was primarily responsible for the origin of life on the Earth? (2012) (a) Hydrogen, Oxygen, Sodium (b) Carbon, Hydrogen, Nitrogen (c) Oxygen, Calcium, Phosphorus (d) Carbon, Hydrogen, Potassium Answer. B Explanation The correct answer to this question, as most of you know, is Carbon, Hydrogen and Nitrogen. In fact, the early biochemistry was not simply the reactions of Carbon, Hydrogen, Nitrogen and Oxygen was a bit far from it, was CO2, N and water resulting in the organic acids such as oxalic acid. The infrared part of solar radiation. The increasing amount of carbon dioxide in the air is slowly raising the temperature of the atmosphere because it absorbs the infrared part of the solar radiation. Only water vapour has the ability to absorb both incoming UV and outgoing infrared radiation. Q.5) A person stood alone in a desert on a dark night and wanted to reach his village which was situated 5 km east of the point where he was standing. He had no instruments to find the direction but he located the polestar. The most convenient way now to reach his village is to walk in the: (2012) (a) direction facing the polestar (b) a direction opposite to the polestar (c) direction keeping the polestar to his left (d) direction keeping the polestar to his right Answer. C Explanation The correct answer is direction, keeping the pole star to his left. In ancient times, people used to determine directions during the night with the help of stars. The North star indicates the north direction. It is also called the Pole Star. Q.6) Variations in the length of daytime and nighttime from season to season are due to - (2013) (a) The earth’s rotation on its axis (b) Revolution of the earth on a tilted axis (c) Latitudinal position of the place (d) The earth’s revolution around the sun in an elliptical manner ©Sarrthi IAS 9569093856 www.sarrthiias.com 16  GS-1 (Geography) Answer. B Explanation Had the axis of the Earth been perfectly perpendicular to the plane of the ecliptic, the sun rays would have been vertical over the equator all year round and the amount of energy received at any place would have remained constant throughout the year; hence no change of seasons. Also in that situation, the days and nights all over the earth would have been exactly equal throughout the year as it happens at the time of equinoxes. The change between day and night is caused by the rotation of the Earth on its axis.... The changing length of days and nights depends on where you are on Earth and the time of year. Also, daylight hours are affected by the tilt of the Earth's axis and its path around the sun. As the Earth moves around the Sun, the length of the day changes.... This is all caused by the 23.5-degree tilt of the Earth's axis as it travels around the sun. In the Northern Hemisphere, days are longest at the time of the summer solstice in June, and the shortest days are at the winter solstice in December. Q.7) Consider the following statements: 1. The Earth's magnetic field has reversed every few hundred thousand years. 2. When the Earth was created more than 4000 million years ago, there was 54% oxygen and no carbon dioxide. 3. When living organisms originated, they modified the early atmosphere of the Earth. Which of the statements given above is/are correct? (2018) (a) 1 only (b) 2 and 3 only (c) 1 and 3 only (d) 1, 2 and 3 Answer. C Explanation A geomagnetic reversal is a change in a planet's magnetic field such that the positions of magnetic north and magnetic south are interchanged. The Earth's field has alternated between periods of normal polarity, in which the predominant direction of the field was the same as the present direction, and reverse polarity, in which it was the opposite. These periods are called chrons. Reversal occurrences are statistically random. There have been 183 reversals over the last 83 million years. The Earth formed approximately 4.5 billion years ago, along with the other seven planets in the solar system. As the Earth cooled, a primitive atmosphere was created by the out-gassing of early volcanoes. The early atmosphere contained no oxygen and would have been toxic to human beings, as well as most other life on Earth today. Based on an analysis of gases vented by modern volcanoes, it seems likely that this early atmosphere consisted mostly of water vapour (H2O) and carbon dioxide (CO2) and nitrogen gas (N2). In the whole process of evolution, the living organism changed the chemical composition of the Atmosphere. For example, oxygen came from photosynthesis. Q.8) On 21st June, the Sun (2019) (a) does not set below the horizon at the Arctic Circle (b) does not set below the horizon at Antarctic Circle (c) shines vertically overhead at noon on the Equator (d) shines vertically overhead at the Tropic of Capricorn Answer. A Explanation The Sun is directly overhead at "high-noon" on the equator twice per year, at the two equinoxes. On the Arctic Circle, the Sun does not set at all on the Summer Solstice which occurs on 21st June. On that one day, the Sun traces a complete circle just above the horizon as the Earth rotates. ©Sarrthi IAS 9569093856 www.sarrthiias.com 17  GS-1 (Geography) INTERIOR OF THE EARTH Why do we need to know about this? Understanding the earth's interior is essential to understanding the nature of changes that take place over and below the earth's surface. To understand geophysical phenomena like volcanism, earthquakes, etc. To understand the internal structure of various objects of the solar system. To understand the evolution and present composition of the atmosphere. Future deep-sea mineral exploration etc. Sources: Direct Sources: Facilitate direct observation of what’s under the surface. ○ Deep Earth mining and Drilling (deepest mine: Mponeng gold mine and TauTona gold mine in South Africa at 3.6km; deepest drilling 12km in Kola peninsula, Russia). ○ Volcanic Eruptions: Bring the material inside the Earth to the surface, giving us an insight into what is present under the Earth. Indirect Sources: Help us statistically extrapolate what’s inside the Earth. ○ Meteors and other celestial bodies (other planets, moons, etc): Similar formation Process as Earth. So, the internal structure of these bodies will be similar to that of the Earth. Helps in expanding our imagination as to how Earth would look from the inside. ○ Gravitation: Gravity value is not the same everywhere, and this is known as a gravitational anomaly; helps us identify material distribution inside the earth. Wherever heavier materials have accumulated, gravitational force will be higher as it is directly proportional to the mass of the bodies in question. ○ Shifts in our magnetic fields: Our magnetic field constantly keeps moving. It reverses in approximately 200000 to 300000 years. It is the material inside the earth that is responsible for the magnetic field. This reversal gives us the idea that the material inside the earth can move. ○ Earthquake waves: Body waves that are generated during earthquakes are by far the best indirect source of information. (Details in the earthquake section.) Other minor sources and observations: ○ Volcanic eruptions and existence of hot springs, geysers etc. point to an interior which is very hot. ○ The high temperatures are attributed to automatic disintegration of the radioactive substances. ○ Gravitation and the diameter of the earth helps in estimating pressures deep inside LAYERS OF EARTH Earth’s layers are identified by studying various direct and indirect sources. The structure of the earth's interior is made up of several concentric layers. Broadly based on chemical properties, three layers of earth can be identified— crust, mantle, and core. ©Sarrthi IAS 9569093856 www.sarrthiias.com 18  GS-1 (Geography) Crust: 30-50km. The outer thin layer of the Earth. It has 2 parts: the denser oceanic (basaltic) and the lighter continental (granitic) crust. The outer covering of the crust is of sedimentary material (granitic rocks) and below that lie crystalline, igneous and metamorphic rocks which are acidic in nature. The lower layer of the crust consists of basaltic and ultra-basic rocks. Oceanic crust (SiMa) denser and thinner (5-30km) Continental Crust (SiAl) lighter and thicker (50-70km). The continental crust is thicker in the areas of major mountain systems. It is as much as 70 -100 km thick in the Himalayan region. The continental and the oceanic crusts are separated by the Conrad discontinuity. It forms 0.5-1.0 per cent of the earth’s volume. Mantle: Mohorovicic Discontinuity to 2900km (Gutenberg Discontinuity). It forms 83% of Earth’s volume. Denser than crust (upper is 2.9-3.3g/cm3; lower is 3.3-5.7g/cm3; average density 4.5g/cm3). The crust and the uppermost part of the mantle are called LITHOSPHERE. Its thickness ranges from 10-200 km. It is Brittle in nature. Below the Lithosphere lies the ASTHENOSPHERE, till 400 km depth. It is a semi-solid molten layer, entirely within the mantle. This layer is the source of Magma. The lower mantle extends beyond the asthenosphere. It is in solid state. The upper and the lower mantle are separated by Repetti Discontinuity. The mantle and the core are separated by Gutenberg Discontinuity. Core: 2900-6400km Lies between 2900 km and 6400 km below the earth's surface. It accounts for 16 per cent of the earth's volume. Core has the heaviest mineral materials of the highest density. It is composed of nickel and iron [NiFe]. The outer core is liquid while the inner core is solid. They are separated by Lehman’s Discontinuity. ©Sarrthi IAS 9569093856 www.sarrthiias.com 19  GS-1 (Geography) Discontinuities: the places inside the Earth’s crust where the seismic waves experience an abrupt change in their velocities and/or direction. PYQ Q.1) How does the Juno Mission of NASA help to understand the origin and evolution of the Earth? (2017, 10m) EARTHQUAKES Abrupt release of energy along a fault causes earthquake waves. A fault is a sharp break in the crustal rock layer. Rocks along a fault tend to move in opposite directions. But the friction exerted by the overlying rock strata prevents the movement of the rock layer. With time pressure builds up. Under intense pressure, the rock layer, at a certain point, overcomes the friction offered by the overlying layer and undergoes an abrupt movement generating shockwaves. This causes a release of energy, and the energy waves travel in all directions. The point where the energy is released is called the focus of an earthquake, alternatively, it is called the hypocentre. The point on the surface, nearest to the focus, is called the epicentre. Earthquake waves: Body Waves and Surface Waves. Recorded by Seismographs installed across the world in Seismic stations. ©Sarrthi IAS 9569093856 www.sarrthiias.com 20  GS-1 (Geography) Body Waves: Generated due to the release of energy at the focus and move in all directions travelling through the body of the earth. P-waves & S-waves are the 2 body waves. The velocity of the Body waves changes as they travel through materials with different elasticity (stiffness) (Generally density with few exceptions). The more elastic the material is, the higher the velocity. Their direction also changes as they reflect or refract when coming across materials with different densities. When an earthquake or underground nuclear test sends shock waves through the Earth, the cooler areas, which generally are rigid, transmit these waves at a higher velocity than the hotter areas. The body waves interact with the surface rocks and generate new sets of waves called surface waves. P-waves: ○ Longitudinal or Compressional Waves ○ Particles of the medium vibrate along the direction of propagation of the wave. ○ Fastest, first to arrive; Primary Waves ○ Their velocity depends on the shear strength or elasticity of the material. ○ Can travel in all mediums: Velocity in Solids > Liquids > Gases. ○ Shadow zone: 103-143 degrees on both sides. ○ This gives clues about Solid inner core S-waves: ○ Transverse or distortional waves. ○ Analogous to water ripples or light waves. ○ Arrive at the surface with some time lag. Secondary waves. ○ Travel at varying velocities (proportional to shear strength) through the solid part of the Earth's crust, mantle. ○ Cannot pass through gases or liquids. ○ Particles move perpendicular to the direction of propagation of the wave. ○ Shadow zone: between 103 degrees and 180 degrees. ○ This observation led to the discovery of a liquid outer core. Since S waves cannot travel through liquid, they do not pass through the liquid outer core. ©Sarrthi IAS 9569093856 www.sarrthiias.com 21  GS-1 (Geography) L-Waves: ○ Love waves. ○ Shear surface waves (transverse like the S-waves) ○ Have the highest velocity of all surface waves and can cause significant horizontal shaking of the ground. ○ 3rd to reach the seismograph. ○ Cause displacement of rocks, and hence, the collapse of structures occurs. R-Waves: ○ Rayleigh Waves. ○ They are characterized by an elliptical or rolling motion that combines both vertical and horizontal particle motion. This motion is similar to the motion of ocean waves. ○ Slowest surface waves and typically cause the most damage during earthquakes due to their strong shaking and rolling motion. ○ Responsible for Tsunamis due to the vertical shift. ©Sarrthi IAS 9569093856 www.sarrthiias.com 22  GS-1 (Geography) Shadow Zones: ○ Earthquake waves get recorded in seismographs located at far-off locations. However, there exist some specific areas where the waves are not reported. Such a zone is called the ‘shadow zone’. ○ The study of different events reveals that for each earthquake, there exists an altogether different shadow zone. ○ It was observed that seismographs located at any distance within 103° from the epicentre, recorded the arrival of both P and S-waves. ○ However, the seismographs located beyond 143 ° from the epicentre, record the arrival of P-waves, but not that of S-waves. ○ Thus, a zone between 103° and 143° from the epicentre was identified as the shadow zone for both types of waves. The entire zone beyond 103 ° does not receive S-waves. ○ The shadow zone of the S-wave is much larger than that of the P-wave. The shadow zone of P-waves appears as a band around the earth between 103 ° and 142 ° away from the epicentre. ○ The shadow zone of S-waves is not only larger in extent, but it is also a little over 40 per cent of the earth's surface. How does this help us determine Earth’s interior ? ○ Reflection causes waves to rebound whereas refraction makes waves move in different directions. ○ The variations in the direction of waves are inferred with the help of their record on seismographs. ○ Change in densities greatly varies the wave velocity. By observing the changes in velocity, the density of the earth can be estimated. ○ By observing the changes in the direction of the waves (emergence of shadow zones), different layers can be identified. Distribution: ○ Mostly at the plate boundaries ○ 2 major belts: Circum-Pacific belt; Mid continental belt. ○ Deep focussed earthquakes at convergent boundaries. ○ Shallow focussed earthquakes at Oceanic Ridge regions and diverging boundaries. How are Earthquakes Measured ? ○ Richter’s Scale: Measures earthquake magnitude by calculating the amplitude of the surface waves generated during the event. It is a logarithmic scale, which means that the amplitude of earthquake waves at Ritcher scale 5 is 10 times less than that at 6. The number indicating magnitude ranges between 0 to 10. ○ Mercalli’s Scale: Measures the intensity of the earthquakes, based on the actual level of destruction caused by the event. The number indicating intensity ranges between 1 to 12 ©Sarrthi IAS 9569093856 www.sarrthiias.com 23  GS-1 (Geography) ○ Moment Magnitude Scale: Most widely used now. Unlike the Richter scale, which measures the amplitude of seismic waves recorded by seismographs, the moment magnitude scale considers the total energy released by an earthquake, including the area of the fault rupture, the average slip along the fault, and the rigidity of the rocks involved. Also, a logarithmic scale. Impact of Earthquakes: Short-term Impacts of Earthquakes ○ Loss of Life and Injuries: Immediate casualties and injuries due to collapsing buildings and infrastructure. ○ Infrastructure Damage: Destruction of buildings, roads, bridges, and utilities. ○ Displacement: Immediate displacement of residents, leading to temporary shelters and emergency relief camps. ○ Economic Disruption: Immediate economic losses due to the halt in commercial activities and destruction of property. ○ Communication Breakdown: Interruption of communication networks and emergency services. ○ Psychological Impact: Immediate trauma and stress among the affected population. Long-term Impacts of Earthquakes ○ Reconstruction Costs: High costs associated with rebuilding infrastructure and homes, often stretching over several years. ○ Economic Recovery: Long-term economic setbacks, including loss of businesses and jobs, and the impact on local and national economies. ○ Population Migration: Long-term displacement can lead to migration and demographic changes. ○ Psychological Effects: Long-lasting mental health issues such as PTSD among survivors. ○ Land Use Changes: Changes in land use patterns, including shifts in residential and commercial areas due to perceived risk. ○ Policy and Preparedness: Implementation of stricter building codes, improved disaster preparedness and response strategies, and increased investment in earthquake-resistant infrastructure. Some recent Earthquakes: Date Location Magnitude Plates Involved Destruction Arabian Plate pushing Southern against Anatolian Devastating earthquake, widespread Feb 6, 2023 Turkey, near 7.8 Plate (Eurasian Plate damage and casualties Syria border fragment) Near Oukaïmeden African Plate and Devastation in remote areas, heavy Sept 8, 2023 e, Morocco 6.8 Eurasian Plate damage in Marrakesh, over 2900 (Atlas boundary deaths Mountains) Noto Philippine Sea Plate Severe shaking, landslides, building Jan 1, 2024 Peninsula, 7.6 subducts under the collapses, tsunami (3ft waves), Japan Eurasian Plate coastline uplift (up to 820ft) ©Sarrthi IAS 9569093856 www.sarrthiias.com 24  GS-1 (Geography) EARTH MOVEMENTS Endogenic Forces: Caused due to the internal energy of the Earth. This energy is mostly generated by radioactivity, rotational and tidal friction 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. Can be of 2 types: Diastrophic and Sudden movements. Diastrophism: bending, folding, warping (bending and twisting of a large area) and fracturing. ○ Orogenic processes involving mountain building through severe folding and affecting long and narrow belts of the earth’s crust. Tension and Compression. Horizontal forces and vertical effects. ○ Epeirogenic processes involving uplift/subsidence or warping of large parts of the earth’s crust. Vertical forces and horizontal effects. Epeirogenic or continent-forming movements act along the radius of the earth; therefore, they are also called radial movements. Their direction may be towards (subsidence) or away (uplift) from the centre. The results of such movements may be clearly defined in the relief. Upliftment examples: Colorado Plateau, Brazilian Highlands, Australian Shield, Siberian Platform. Subsidence examples: Siberian Basin, Kachchh region. ○ Orogeny is a mountain-building process whereas epeirogeny is a continent-building process. Sudden Movements: ○ Include earthquakes and volcanism involving local relatively minor movements. ○ Due to their sudden-ness, cause a large amount of destruction, and are included under natural disasters. ○ Can also cause upliftment or submergence. ○ The 2004 Indian Ocean earthquake caused Indira Point to submerge. An earthquake in New Zealand (1885) caused an upliftment of up to 3 metres in some areas while some areas in Japan (1891) subsided by 6 metres after an earthquake. Through the processes of orogeny, epeirogeny, earthquakes and plate tectonics, there can be faulting and fracturing of the crust. All these processes cause pressure, volume and temperature (PVT) changes which in turn induce the metamorphism of rocks. ©Sarrthi IAS 9569093856 www.sarrthiias.com 25  GS-1 (Geography) Exogenic Forces: A direct result of stress induced in earth materials due to various forces that come into existence due to the sun's heat. Temperature and precipitation are the two important climatic elements that control various processes by inducing stress in earth materials. ○ Weathering, Erosion, Deposition & Mass Movement. Denudation All the exogenic geomorphic processes are covered under a general term, denudation. Types of Weathering: Chemical: Change in chemical composition ○ Solution: Rocks formed of water-soluble minerals. Soluble rock-forming minerals like nitrates, sulphates, potassium, etc. are affected. ○ Carbonation: CO2 and water form Carbonic acid, which reacts with rocks. ○ Hydration: Hybrid form of weathering. Addition of water to mineral expands it, and removal contracts it. Fatigue causes disintegration. ○ Oxidation: combination of a mineral with oxygen to form oxides. Iron, Manganese, Sulphur rich rocks experience this. ○ Reduction: When oxidized minerals are placed in an environment where oxygen is absent. E.g. Red iron oxides turn greenish or bluish grey. Physical: ○ Due to gravity, temperature and moisture changes, agents of erosion, biological activity. ○ Unloading and Expansion ○ Granular Disintegration (sedimentary rocks): Rocks composed of coarse mineral grains commonly fall apart grain by grain or undergo granular disintegration. ○ Exfoliation (diurnal temperature changes): With rise in temperature, every mineral expands and pushes against its neighbor and as temperature falls, a corresponding contraction takes place. Because of diurnal changes in the temperatures, this internal movement among the mineral grains takes place regularly. ©Sarrthi IAS 9569093856 www.sarrthiias.com 26  GS-1 (Geography) This process is most effective in dry climates and high elevations where diurnal temperature changes are drastic. The surface layers of the rocks tend to expand more than the rock at depth and this leads to the formation of stress within the rock resulting in heaving and fracturing parallel to the surface. Exfoliation results in smooth rounded surfaces in rocks. ○ Block separation: This type of disintegration takes place in rocks with numerous joints acquired by mountain-making pressures or by shrinkage due to cooling. This type of disintegration in rocks can be achieved by comparatively weaker forces. ○ Shattering (angular pieces): A huge rock may undergo disintegration along weak zones to produce highly angular pieces with sharp corners and edges through the process of shattering. This occurs when there is a temperature change; when the rock is exposed to the effects of wind, rain and waves also contributes to disintegration. ○ Frost wedging: During the warm season, the water penetrates the pore spaces or fractures in rocks. During the cold season, the water freezes into ice and its volume expands as a result. This exerts tremendous pressure on rock walls to tear apart even where the rocks are massive. Frost weathering occurs due to the growth of ice within pores and cracks of rocks during repeated cycles of freezing and melting. ○ Salt weathering (crystallization): Salts in rocks expand due to thermal action, hydration, and crystallisation. Many salts like calcium, sodium, magnesium, potassium, and barium tend to expand. High-temperature ranges in deserts favour such salt expansion. Salt crystals in near-surface pores cause the splitting of individual grains within rocks, which eventually fall off. This process of falling off of individual grains may result in granular disintegration or granular foliation. Biological: Burrowing and wedging exposes more surface for physical or chemical weathering Physical weathering by plant roots Human actions Decaying plant and animal matter help in the production of humic, carbonic, and other acids which enhance decay and solubility of some elements. Removal of minerals by algae and plants. Mass movements: ○ Movement of material ONLY under the impact of gravity. ©Sarrthi IAS 9569093856 www.sarrthiias.com 27  GS-1 (Geography) Significance of Denudation: Soil formation and enrichment Helps in the enrichment and concentrations of certain valuable ores of iron, manganese, aluminium, copper etc. Degradation and Aggradation PYQ Q.) Consider the following statements : 1. In a seismograph, P waves are recorded earlier than S waves. 2. In P waves, the individual particles vibrate to and fro in the direction of Wave propagation whereas. in S waves, the particles vibrate up and down at right angles to the direction of wave propagation. ©Sarrthi IAS 9569093856 www.sarrthiias.com 28  GS-1 (Geography) Which of the statements given above is/are correct? (2023) (a) 1 only (b) 2 only (c) Both 1 & 2 (d) Neither 1 nor 2 Ans: C Explanation: P or Primary waves are the fastest seismic waves, thats why they are the first to be received. P waves are longitudinal, i.e. direction of propagation of waves and the direction of movement of particles is the same. S waves are transverse i.e. particles move perpendicular to the movement of the wave. CONTINENTAL DRIFT & SEA FLOOR SPREAD THEORIES PLATE TECTONICS Earlier Theories: Permanency Theory Works of Antonio Pellegrini (1858): identical fossil plants in North American and European coal deposits could be explained if the two continents had formerly been connected. Edward Suess (late 19th century): large ancient continents had been composed of several of the present-day smaller ones Continental Drift Theory by F. B. Taylor: arcuate (bow-shaped) mountain belts of Asia and Europe resulted from the creep of the continents toward the Equator. Continental Drift Theory By Alfred Wegener in 1912. There existed one big landmass which he called Pangaea which was covered by one big ocean called Panthalassa. Later, a sea called Tethys divided the Pangaea into two huge landmasses: Laurentia (Laurasia) to the north and Gondwanaland to the south of Tethys. Assumptions: ○ Free Float of SiAl over SiMa. ○ Oceanic Crust was passive. ○ Forces responsible: Tidal force (caused the Westward Movement) & Gravity + Polar Fleeing Force (caused the Equator-ward Movement). Tidal forces played a bigger role. ○ Disintegration of Pangea in the Triassic Period (251-199.6 mya; Mesozoic Era). Arguments supporting the theory: ○ Jigsaw fit of shape: South America and Africa seem to fit in with each other, especially, the bulge of Brazil fits into the Gulf of Guinea. Greenland seems to fit in well with Ellesmere and Baffin islands. The east coast of India, Madagascar and Africa seem to have been joined. ○ Jigsaw fit of structure (rocks, minerals and fossil deposits): The Caledonian and Hercynian mountains of Europe and the Appalachians of the USA seem to be one continuous series. ©Sarrthi IAS 9569093856 www.sarrthiias.com 29  GS-1 (Geography) Radiometric Dating has confirmed the presence of similar rocks, 2 billion years old, on both the Brazilian coast as well as West African Coast. Rich placer deposits of gold are found on the Ghana coast (West Africa), but the source (gold-bearing veins) is in Brazil and it is obvious that the gold deposits of Ghana are derived from the Brazil plateau when the two continents lay side by side. Mesosaurus was a small reptile adapted to shallow brackish water. The skeletons of these are found only in South Africa and Iraver formations of Brazil. The two localities presently are 4,800 km apart with an ocean in between them. ○ Paleoclimatic Evidence: Tillite sedimentary rock formed out of deposits of glaciers. The Gondwana system of sediments from India is known to have its counterparts in six different landmasses of the Southern Hemisphere. The glacial Tillite provides unambiguous evidence of paleoclimates and of the drifting of continents. ○ Paleomagnetic evidence (will be covered below) Drawbacks: ○ No free float of SiAl over SiMa. It is the lithosphere that moves over the Asthenosphere. ○ Ocean Floor is not passive: Hess’s Sea Floor Spread Theory. ○ Tidal and Gravitational Forces are not enough to cause such massive land masses to move. Convective Currents cause this movement. ○ He talked about the movement of landmasses only towards the Equator, and the West direction, when the movement was seen in all directions. E.g. Antarctica moved away from the Equator, and Australia moved East. Moreover, India moved in the Northeast direction, initially towards the equator, and later passing it altogether. ○ Did not mention why the Pangea suddenly broke only precisely in the Triassic period. Why did nothing happen before it? Seafloor Spread Theory: By Harry Hess in 1960. Detailed research during World Wars revealed that the ocean floor is not just a vast plain but it is full of relief with mountain ranges, deep trenches, etc. The mid-oceanic ridges were found to be most active in terms of volcanic eruptions. Mid-oceanic ridges prove that ocean floors are not static. Rocks on either side of the crest of oceanic ridges and having equidistant locations from the crest were found to have remarkable similarities both in terms of their constituents and their age. Shallow focus earthquakes at mid-oceanic ridge areas. (Deep focus EQs at the Himalayan belt) Oceanic rocks are much younger than continental, as former subduct. ©Sarrthi IAS 9569093856 www.sarrthiias.com 30  GS-1 (Geography) Convectional Current Theory Arthur Holmes in the 1930s According to this theory, the intense heat generated by radioactive substances in the mantle (100-2900 km below the earth's surface) seeks a path to escape and gives rise to the formation of convection currents in the mantle. Rising limbs 🡪 divergence; falling limbs 🡪 convergence Paleomagnetism Certain minerals in rocks lock in a record of the direction and intensity of the magnetic field when they form. Give details of both age and the location of formation of the rocks. Basaltic rocks formed in the sea floor spread regions contain magnetic material that locks in the information. Paleomagnetic studies of rocks and ocean sediment have demonstrated that the orientation of the earth's magnetic field has frequently alternated over geologic time. Periods of "normal" polarity (i.e., when the north-seeking end of the compass needle points toward the present north magnetic pole, as it does today) have alternated with periods of "reversed" polarity (when the north-seeking end of the compass needle points southward). As today's magnetic field is close to the earth's rotational axis, continental drift could be tested by ascertaining the magnetic characteristics of ancient rocks. When paleomagnetists [scientists who study past magnetic fields], took a look at the ocean floor going out away from oceanic ridges (either side of the oceanic ridges), they found magnetic stripes that were flipped so that one stripe would be normal polarity and the next reversed. As the new rock is formed near the ridge, older rock, which formed millions of years ago when the magnetic field was reversed, got pushed farther away, resulting in this magnetic striping. When Earth’s geomagnetic field undergoes a reversal, the change in polarity is recorded in the magma, which contributes to the alternating pattern of magnetic striping on the seafloor. PYQ Q.1) Which of the following phenomena might have influenced the evolution of organisms ? 1. Continental drift 2. Glacial cycles Select the correct answer using the code given below. (2014) (a) 1 only (b) 2 only (c) Both 1 and 2 (d) Neither 1 nor 2. ©Sarrthi IAS 9569093856 www.sarrthiias.com 31  GS-1 (Geography) Ans. C About 200 million years ago, all the continents on Earth were actually one huge "supercontinent" surrounded by one enormous ocean. This gigantic continent, called Pangaea , slowly broke apart and spread out to form the continents we know today. All Earth's continents were once combined in one supercontinent, Pangaea. One of the most prominent examples of the effect of continental drift on the evolution of organisms is the unique primates found in Australia and South America. The final stages of evolution of Genus Homo occur in the last 3 glacial cycles. Mains Qn: Q.1) What do you understand by the theory of continental drift? Discuss the prominent evidences in its support. (2013, 5m) PLATE TECTONICS THEORY First suggested by McKenzie and Parker in 1967 First outlined by Morgan in 1968. Both ‘convectional current theory’ and ‘seafloor spreading’ paved the way for the Theory of Plate Tectonics. Theory: Lithosphere is broken into multiple plates (7 major, numerous minor) It floats on the Asthenosphere under the impact of Convectional Currents. Lithospheric plates (sometimes called crustal plates, or tectonic plates) vary from minor plates to major plates, continental plates (Arabian plate) to oceanic plates (Pacific plate), and sometimes a combination of both continental and oceanic plates (Indo-Australian plate). The oceanic plates contain mainly the Simatic crust and are relatively thinner, while the continental plates contain Sialic material and are relatively thicker. Major Plates: ○ Antarctica and the surrounding oceanic plate ○ North American plate ○ South American plate ○ Pacific plate ○ India-Australia-New Zealand plate ○ Africa with the eastern Atlantic floor plate ○ Eurasia and the adjacent oceanic plate Minor Plates: There are many more minor plates other than the above-mentioned plates. Most of these minor plates were formed due to stress created by converging major plates. For example: the Mediterranean Sea is divided into numerous minor plates due to the compressive force exerted by the Eurasian and African plates. Forces for plate movement: the convectional currents. Arthur Holmes gave the idea about these in 1930s. Explains Earthquakes, Volcanoes, Fold and Block Mountains 70% earthquakes; 90% of volcanoes (75% active) in the Circum-Pacific Ring of Fire. Circum-Pacific Ring of Fire: ○ The boundary of the Pacific plate, where it is subducting beneath the Indo-Australian, Eurasian, and American plates. ○ From New Zealand to Chile. 20% earthquakes in Mid-Continental region. The Arctic Ridge has the slowest rate (less than 2.5 cm/yr), and the East Pacific Rise in the South Pacific [about 3,400 km west of Chile], has the fastest rate (more than 15 cm/yr). ©Sarrthi IAS 9569093856 www.sarrthiias.com 32  GS-1 (Geography) Plate Boundaries: Major geomorphological features such as fold and block mountains, mid-oceanic ridges, trenches, volcanism, earthquakes etc. are a direct consequence of interaction between various lithospheric plates. Diverging/Constructive Boundaries: ○ The sites where the plates move away from each other are called spreading sites. ○ Such edges are sites of earth crust formation (hence constructive) and volcanic landforms are common along such edges. ○ Earthquakes (shallow focus) are common along divergent edges. ○ Examples: Mid-oceanic ridges (some of the longest mountain ranges of the world); On land, most prominent: Great African Rift Valley (divergence of African and Somali Plate; Lebanon in North to Mozambique in South.) ○ Leads to the formation of Volcanoes, Block Mountains and in case of Mid Oceanic ridges, volcanic Islands, like the Azores on the Mid-Atlantic Ridge. Converging/Destructive Boundaries: ○ 2 types: C-C Convergence: When it's Continent-Continent Convergence, it's called a colliding boundary. E.g., Indian and the Eurasian Plates O-C Convergence (aka Cordilleran convergence, as leads to formation of fold mountains on the continental plate): When its Ocean-Continent Convergence, it’s called a subducting boundary. E.g. Pacific Ocean and South American Plate. ○ The zone of collision may undergo crumpling and folding, and folded mountains may emerge. ○ When one of the plates is an oceanic plate, it gets embedded in the softer asthenosphere of the continental plate and as a result, trenches are formed at the zone of subduction. ○ The subducted material gets heated up and is thrown out forming volcanic islands and dynamic equilibrium is achieved. ○ Destructive: Subduction of the denser plate under the less dense one. ○ Colliding: E.g. Himalayas ○ Lead to the formation of Fold mountains, and in case of O-C convergence, formation of Oceanic Trenches and Volcanoes too. ○ Why are there no volcanoes in colliding boundaries? Since no subduction, no molten material is available to burst out from the volcanoes. That is why the Himalayas do not have any volcanoes, while the Andes and the Alps do! Transforms/Conservative: ○ Formed when two plates move past each other. ○ In this kind of interaction, two plates grind against each other and there is no creation or destruction of landform but only deformation of the existing landform. [Crust is neither produced nor destroyed as the plates slide horizontally past each other]. ©Sarrthi IAS 9569093856 www.sarrthiias.com 33  GS-1 (Geography) ○ No creation or destruction. Only deformation. ○ Generally perpendicular to oceanic ridges. ○ The San Andreas Fault along the western coast of the USA is the best example. Indian Plate: ○ Indo-Australian Plate. ○ East Margin: through Rakin Yoma Mountains (Arakan Yoma) of Myanmar towards the island arc along the Java Trench. ○ West Margin: Kirthar mountains of Pakistan ○ Northern Margin: Himalayas ○ Eurasia plate on its northern and eastern boundary; Arabian plate on its, western boundary; Somalia, Capricorn, and Australia plates to the south ○ Movement of Indian Plate: India was a large island situated off the Australian coast, in a vast ocean. The Tethys Sea separated it from the Asian continent till about 225 million years ago. India is supposed to have started her northward journey about 200 million years ago at the time when Pangaea broke. India collided with Asia about 40-50 million years ago causing rapid uplift of the Himalayas. About 140 million years before the present, the subcontinent was located as south as 50◦ S. latitude. The two major plates were separated by the Tethys Sea and the Tibetan block was closer to the Asiatic landmass. During the movement of the Indian plate towards the Asiatic plate, a major event that occurred was the outpouring of lava and formation of the Deccan Traps. This started somewhere around 65 million years ago and continued for a long period. Note that the subcontinent was still close to the equator. From 40-50 million years ago (disputed by some experts who say it started around 60 million years ago) and thereafter, the event of formation of the Himalayas took place. Scientists believe that the process is still continuing and the height of the Himalayas is rising even to this date. Comparing Continental Drift, Plate Tectonic And Sea Floor Spread Theories ©Sarrthi IAS 9569093856 www.sarrthiias.com 34  GS-1 (Geography) PYQ Q.) Consider the following: 1. Electromagnetic radiation 2. Geothermal energy 3. Gravitational force 4. Plate Movements 5. Rotation of the earth 6. Revolution of the earth Which of the above are responsible for bringing dynamic changes on the surface of the earth? (2013) (a) 1, 2, 3 and 4 only (b) 1, 3, 5 and 6 only (c) 2, 4, 5 and 6 only (d) 1, 2, 3, 4, 5 and 6 Ans. D All the factors are responsible for bringing dynamic changes on the surface of the earth. Wind, water, and ice erode and shape the land. Volcanic activity and earthquakes alter the landscape in a dramatic and often violent manner. And on a much longer timescale, the movement of earth's plates slowly reconfigures oceans and continents. Each one of these processes plays a role in the Arctic and Antarctica. Electro-magnetic radiation causes temperature change which induces metamorphism of rocks. Gravity besides being a directional force activating all down slope movements of matter also causes stresses on the earth’s materials. Plate movement results into continent building. The energy emanating from within the earth is the main force behind endo-genic geomorphic processes. This energy is mostly generated by radioactivity, rotational and tidal friction 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 variations in geothermal gradients and heat flow from within, crustal thickness and strength, the action of endo-genic forces are not uniform and hence the tectonically controlled original crustal surface is uneven. VOLCANISM Volcanism: The process by which molten rock material from the asthenosphere finds a way to enter the lithosphere, where it may or may not reach the surface of the Earth. A volcano is a vent in the earth's crust from which molten rock material (magma), explosive bursts of gases and volcanic ashes erupt, or A mountain or hill having a crater or vent through which lava, rock fragments, hot vapour, and gas are or have been erupted