Geography UPSC Notes Complete

Origin and Evolution of Earth

Big Bang Theory

The most scientific theory which explains origin of universe is Big Bang Theory. It was given by Georges Lemaître, a Belgian physicist in 1927. According to this theory the universe came into being about 13.8 billion years ago after a big explosion that is called Big Bang.

• Before Big Bang the present universe was confined into an atom-sized speck/ ball.
• This was stage of singularity. Singularity means the stage when there is no space no time no matter exists.
• During this time there was infinite pressure, temperature, and density.
• The four fundamental forces which govern the entire universe were also combined together. It includes:-
  1. Gravity:- Gravity pulls objects with mass towards each other. Due to this force, planets are orbiting stars.
  2. EM-force:- It acts between electrically charged particles. It is responsible for lightning, electricity, etc.
  3. Strong Nuclear force:- It binds quarks together to form protons and neutrons. Without this force atoms could not exist.
  4. Weak Nuclear force:- It plays a key role in nuclear reaction. It has been converting one type of particle into another. It causes certain types of radioactive decay.
• About 13.8 billion years ago this atom-sized speck started expanding, this event is called the Big Bang.
• The expansion of this universe was initially relatively slow. This time is called the Planck Era ( 0 to 10^-43 second).
• After Planck's era a universe expands enormously in a tiny fraction of seconds, that is, about 10^-36 to 10^-32 seconds. This phase is called the phase of cosmic inflation.
• Thereafter a universe keeps on expanding even at the present but with relatively slower speed.
• Due to continuous expansion, universe density, temperature, and pressure decreases, in other words, cooling of the universe started.
• After the Big Bang, the fundamental forces also got separated. The force of gravity was the first one to operate.
• Due to cooling of the universe, electrons, protons, and neutrons were formed, which later on combined to form the first atom. The first element was Hydrogen, followed by Helium.
• The large clouds of Hydrogen, Helium led to the formation of galaxies and stars, and this way the universe came into being.

Main Evidence

1. Redshift theory:- It was given by Edwin Hubble in 1929. According to this theory, when a source of light moves away from an observer, its light waves get stretched and the wavelength becomes longer and shifts towards the end of the visible spectrum. Hubble observed that the stars of the distant galaxies are moving away from us, thus the universe is expanding.
2. Cosmic Microwave Background Radiation:- It was given by Wilson and Penzias in 1965. They found that Cosmic Microwave Background Radiation is left over thermal radiation from the early universe. Because of this radiation, the temperature of the universe is 2.7 K, which is nearly the same temperature in all directions. It means the universe had an origin.
3. Presence of light Elements in the Universe:- It is one of the strongest evidence for the Big Bang. According to this, the universe is filled with hydrogen (75% by mass) and helium (25% by mass).

Limitations

1. Can not explain singularity.
2. Can not explain what happens before the Big Bang.
3. Was there only the Big Bang or multiple Big Bangs, Only universe or multiverse?

Steady State Theory of Origin of Universe

It was proposed in 1948 by Hoyle, Bondi and Gold. According to this

• Universe has always existed and will always i.e. it is permanent.
• The universe is expanding but its overall appearance remains same over time.
• The galaxies move apart, new matter is continuously created in empty space to maintain a constant average density.

Difference between Big Bang Theory and Steady State Theory

Steady State Theory has now been completely discarded especially after discovery of cosmic microwave background radiation.

Galaxies

• Galaxies are huge groups of stars or vast collection of stars, planets, gas, dust, etc. held together by the gravity. There are 3 types of galaxies:
  1. Spiral Shape Galaxy:- Such galaxies have arms e.g. Milky Way galaxy has 6 arms. Our solar system lies in Orion Arm. Similarly our nearest galaxy Andromeda.

  2. Elliptical Shape:- e.g. Cygnus A
  3. Irregular shape Galaxies:- Such galaxies do not have any particular shape e.g. Magellanic Clouds Large and Small. These two galaxies are satellite galaxies of the Milky Way.
• There is a presence of high gravity in the centre of galaxy which are mostly black holes e.g. name of the black hole present in the centre of the galaxy, Milky Way, is Sagittarius A.
• Galaxies have their peripheral which are called cradles or birthplace of star from where new stars are formed.
• Quasar is one of the brightest object in universe. It is extremely bright centre powered by supermassive black hole.
• Our Milky Way galaxy is a part of local group which contains 52 to 54 galaxies. Local group is part of Virgo Supercluster.
• Virgo Supercluster is part of Laniakea Supercluster. Eventually part of Pisces-Cetus Supercluster Complex.

Stars

Nebula

Star forming Nebula is a vast cloud of gas and dust in space where new stars are born. Gravity causes parts of the cloud to collapse which forms a Protostar out of the Nebula.

Protostar

A Protostar is a young, developing star formed when a dense region within a Nebula collapses under gravity. It is not yet a true star because nuclear fusion has not started in its core. As it contracts and heats up, it eventually reaches the temperature needed for fusion.

T Tauri Stage

It is a very young star in the final stage before becoming a Main Sequence star. It has an age usually less than 10 million years.

Main Sequence Star

A main sequence star is a stable star that produces energy by converting hydrogen into helium in its core through nuclear fusion. This is the longest stage in the star lifecycle. Our sun is in Main Sequence star stage. Our Sun had become a Main Sequence star about 4.5 billion years ago. Cepheid Variable:- It is not a separate stage in the life cycle of all stars. It is a type of pulsating star that is usually found after the main sequence phase. The star repeatedly expands and contracts, causing its brightness to vary regularly.

Red Giant and Super Red Giant Star

1. Red Giant:- Small and medium-sized stars, which lose their fuel gradually, which has mass up to maximum 8 solar masses enter into the stage of red giant. In this stage, the star becomes much larger than the main sequence star.
2. Super Red Giant:- Large stars which consume their fuel faster than small stars, which have mass more than 8 times of solar mass enter into the stage of super red giant. In this stage, the size of the star becomes very large due to nuclear fusion of heavier elements like helium, carbon, oxygen, etc., in successive stages.

Planetary Nebula Stage

Small stars enter into this stage after red giant stage. In this a small core remains at the centre and the outer periphery gradually blows away.

White Dwarf

It is the end stage of small stars.

Supernova Explosion Stage

After the super red giant stage, large stars enter into the supernova stage, i.e., a supermassive explosion. It produces and disperses heavy elements such as iron, gold, uranium, etc.

Neutron Star

It is formed when the mass of the dying star is 8 to 25 solar masses.

Pulsar Star

It is subtype of neutron star. Neutron stars are made up of neutrons. When it releases huge amount of radiation it is called pulsar star.

Black Hole

It is the end stage of a dying star if its mass is more than 25 solar masses (20 to 25 solar masses). Black holes are the reason for massive gravity; even light cannot escape. If it goes or enter into event horizon of black hole. The centre of the black hole is called Singularity no space, no matter, no time.

Solar System

Sun (Star) Planets (Satellites) Dwarf Planets Asteroids Meteors Comets Kuiper Belt Oort Cloud

Sun

Sun Spots

Sunspots are those special places developed on the Sun's surface which have abnormally high electromagnetic activity. This is why the amount of heat from these areas is less than the average. These have relatively low temperatures. The darkest part in the centre of the sunspot is called the Umbra and the relatively less dark part is called the Penumbra. Sunspots go from minimum to maximum in an 11-year cycle. In every 11^th year, the Sun's magnetic polarity also reverses. When the number of sunspots is recorded at maximum, the amount of radiation is also recorded at maximum, and vice versa.

Solar winds

Solar winds are a stream of plasma particles that are ejected from the sun's atmosphere. They are caused by the sun's magnetic field and they can cause Aurora on earth poles.

Solar Flares

Solar flares are an intense burst of radiation that is caused by the release of magnetic energy from sunspots.

Solar Prominence

These are enormous, arching structure of hot, glowing gas that extends from the sun's surface to its outer atmosphere. They are often seen during total solar eclipse.

Planets

The heliocentric theory was given by Copernicus, and Kepler was the first to explain and prove that planets revolve around the Sun in elliptical paths. That is why there is a concept of Perihelion and Aphelion. Earth reaches its Aphelion on 4^th July and Perihelion on 3^rd January. Definition of Planet

• Objects which revolve around the Sun
• Should have sufficient gravity to give spherical shape
• It must have clear neighbourhood (of orbit)

Mercury

• Mercury is the first planet from the sun.
• It is about 55% the mass of the earth.
• It has about 38% of earth's gravity.
• It has prograde rotation i.e. west to east.
• It is the second hottest planet in the solar system.
• It has no moon.

Venus

• It is second planet from the sun.
• It is considered as earth's twin because of almost similar size and mass.
• It has retrograde rotation i.e. east to west.
• It completes its one rotation in 243 earth days i.e. the slowest rotation among the major planets.
• It completes its one revolution in 225 earth days, thus a day is longer than the year on Venus.
• Venus is the hottest planet of the solar system because it has a very high concentration of greenhouse gases (CO₂, i.e., about 96.5%). If it rains on Venus, it is mainly carbonic acid or sulphuric acid.
• The average temperature of Venus is 465° C.
• It is brightest planet also. It is called morning and evening star.
• It is called goddess of beauty.
• It has no satellite.

Earth

• Third Planet.
• Its average density is 5.5g/cm³.
• Only planet where water is found in liquid state. It is because of its ideal temperature.
• It has an ideal temperature because it is situated at an ideal distance from the Sun. This ideal distance is called the habitable zone or Goldilocks zone.
• It has one natural satellite called moon.
• Moon was formed 4.4 billion years ago whereas earth was formed 4.5 billion years ago.
• The Moon revolves around the Earth in about 27 days, and it takes almost the same time to complete its rotation as well.
• Earth's average orbital speed is about 30 km/s.
• Escape velocity from the earth is 11.2 km/s.

Mars

• It is fourth planet from the sun.
• It is called red planet because it contains red rock that is because of oxidation.
• It completes its rotation in 24 hours and 37 minutes, which is very close to Earth's rotation (Earth sidereal day is 23 hours 56 minutes 4 seconds, Earth solar day is 24 hours )
• Mars has 2 moons. Deimos and Phobos.
• Earlier mars had strong magnetic field (billions of years ago) but now it does not have strong magnetic field.
• Largest volcano of solar system is Olympus Mons and this is on mars.

Jupiter

• It is fifth planet from the sun.
• It is gas giant
• It has 318 times greater mass than the earth.
• It has faint ring.
• It has 95 moons
• It is the largest planet of solar system.
• It is made up of hydrogen 90%, helium 10%. It has trace amounts of methane, ammonia and water vapour.
• It completes one rotation in 9 hours 56 minutes. This makes it the fastest rotating planet in the solar system.
• It completes one revolution in 11.86 years, or on average 12 years. That's why Kumbh Mela is celebrated after every 12 years at 4 places
  1. Haridwar, Ganga river
  2. Prayagraj , Ganga river
  3. Ujjain , Shipra river
  4. Nashik, Godavari river
• Its important moons are
  • Io - most volcanically active body in the solar system.
  • Europa
  • Ganymede - It is bigger than mercury. It is largest moon in the solar system.
  • Callisto

Saturn

• It is sixth planet from the sun.
• It is gas giant.
• It has prominent ring.
• It has 270+ moons. Major moons are:
  • Titan - It is the second largest moon of the solar system, larger than Mercury.
  • Enceladus - It is covered with ice.
  • Rhea
  • Iapetus
  • Dione
  • Mimas
• Second largest planet in solar system made of 96% hydrogen and 3% helium.
• It completes its rotation in 10.7 hours, or about 10 hours 33 minutes.
• It completes its revolution in 29.5 years.
• On the North Pole of Saturn storms are developed in hexagon shape.
• The density of Saturn is less than water

Uranus

• Seventh planet
• It is an ice giant.
• It has 28 moons. Important moons are
  • Titania - Largest moon of Uranus.
  • Oberon
  • Ariel
  • Miranda Most of the moons are named after characters from William Shakespeare's plays.
• Its colour is blue-green. The reason behind the blue colour of Uranus is the high presence of methane gas. Methane gas absorbs red light and reflects blue-green light.
• Uranus is third largest by diameter and fourth largest by mass.
• Its rotation is retrograde, i.e., east to west like Venus.
• It completes its rotation in 17 hours 14 minutes and its revolution in 84 years.
• Uranus is tilted on its axis by about 98°.
• It has also a faint ring.

Neptune

• It is eighth and farthest from the sun.
• It is an ice giant.
• It has about 16 moons. Its famous moons are-
  • Proteus
  • Larissa
  • Nereid
• It has faint rings.
• It has blue colour.
• It rotates west to east and completes its one rotation in 16 hours and completes one revolution in 165 Earth years.
• Neptune experiences fastest wind blow of our solar system sometimes faster than 2000 km/h.

Dwarf Planets

Dwarf planets are those which

• revolve around the Sun
• have spherical shape
• but do not have a cleared orbit/neighbourhood. There are five dwarf planets.

1. Pluto - Largest one.
2. Makemake
3. Haumea
4. Eris These four lie in Kuiper Belt
5. Ceres - Smallest dwarf planet. It lies in asteroid belt

Asteroid Belt

The Asteroid Belt is a region of the solar system which lies between Mars and Jupiter. It contains millions of rocky substances including ceres. These are also revolving around the sun.

Meteors

Meteors are rocky substances that are attracted by Earth's gravity and enter Earth's atmosphere. There in the mesosphere, due to high friction of the air, they catch fire, and they are called shooting stars. Most of them are completely burned and change into ashes, and only a few of them hit the Earth's surface. If a number of meteors come together and start burning in the mesosphere, it is called a meteor shower.

Comets

Comets are small celestial bodies primarily made up of ice and dust. When they approach the Sun while revolving, the head starts glowing; this glowing head is called a coma. Because of the evaporation of the ice, they develop a tail, which is called a dust tail. The central rocky part is the nucleus. Comets come from mainly two places

1. the Kuiper Belt, which is located beyond Neptune. From here short period comets come
2. Oort Cloud - from here long period comets come which have time greater than 200 years. The very famous comet called Halley's Comet comes every 76 years; it last appeared in 1986 and is expected again in 2061.

Oort Cloud

It is a cloud that surrounds or envelops the entire solar system. It was first proposed by Jan Oort in 1950s.

Earth

Earth has a geoid shape. Its geoid shape is explained as:

• Earth like shape which is unique.
• It has spherical shape/ Spheroid but it is not a perfect sphere because it has flattening at the poles because of maximum centripetal and centrifugal forces.

Motion of Earth

1. Rotation Earth rotates on axis and completes its rotation in 24 hours called solar day or in 23 hours 56 minutes and 4 seconds called sidereal day. Earth completes its rotation on its axis which is tilted at 23.5 degrees at present. However, according to Milankovitch cycle the Earth's axial tilt varies between 22.1° and 24.5° in a time span of 41000 years. There is another motion on the Earth's axis, which occurs due to wobbling in the Earth. This motion is called precession, which completes one cycle in a time frame of 26 thousand years.
2. Earth Revolution Revolution is the motion of the Earth around the Sun. In its orbit, the Earth completes one orbit in 365.25 days. Because of the orbiting motion (i.e., revolution) as well as the tilt of the Earth, it experiences seasonal changes. Revolution and rotation both cause dynamic changes on the Earth's surface; rotation causes day and night as well as flattening at the poles and bulging at the equator. Eccentricity is about the change in the shape of Earth's orbit which goes from near circular to highly eccentric in time frame of 100,000 years. Eccentricity/ Obliquity/ Precession influenced the amount of insolation reaching on earth. In other words they affect climate change.

Longitude and Latitude

Time Zones

• Many countries in the world have more than one time zone because of high longitudinal extent or east to west expansion of their geographical area. e.g., Russia has more than 10 time zones, and the US has more than 5 time zones. However, France has the maximum number of time zones, especially because of its colonial past. India has only one time zone: IST (Indian Standard Time), which is based on the longitude of 82.5° E near Mirzapur/Prayagraj, Uttar Pradesh. This means that the entire country, from Gujarat in the west to Arunachal Pradesh in the east, uses the same clock time. However, the longitudinal distance between the westernmost and easternmost parts of India is about 30°. That's why a debate is going on in the country about having two time zones in India.

Why India should have two time zones?

1. Huge difference in sunrise and sunset
   1. Dong in Arunachal Pradesh experiences sunrise during summers at 4 AM approximately
   2. Bhuj of Gujarat experiences sunrise around 6 AM during summers As a result sun rises nearly two hours earlier in eastern India than in western India. Due to this people in Northeast India start their day much earlier besides this offices and school open after sunrise by a large margin which causes loss of or wastage of valuable daylight
2. Energy Savings: Research by India's scientific agencies and studies by the government expert committee suggest that advancing time in the north east could save electricity. The National Institute of Advanced Studies i.e. NIAS, Bengaluru estimated annual savings of around 200 to 270 million units if eastern India adopts a separate time zone. By doing this less artificial light is needed in the evening.
3. Better productivity and health: People naturally function according to daylight this is called circadian rhythm. In the Northeast early sunrise but late office timing create a mismatch. Children often go to school long after sunrise. Workers lose their productivity because of late start in the morning. Thus, aligning clock time with sunlight can improve sleep cycle, work productivity and health outcomes.
4. Many large countries have multiple time zones e.g. Russia, US, Canada, Australia, etc.

Why India should not have two time zones?

1. Railways and Aviation safety: India operates one of the world's largest railway networks. Historically before independence different cities of India had different time zones like Bombay time, Calcutta time, Madras time, etc. This was creating a lot of confusion. Today over 13 thousand passenger trains run daily and thousands of flights operate annually. Creation of two time zones could increase scheduling complexity and risk of error.
2. Administrative complexities: If Assam follows one time and Bihar another it would make it very difficult to operate government offices, banks, courts, national examination, stock markets etc.
3. Economic Integration: India is highly integrated economically. Thus every business prefer one clock, one market opening time and one office schedule. Multiple time zones may increase coordination costs.

Alternate solution

Instead of changing clock or time zones we can reschedule office time, school time and most things 1 or $\frac{1}{2}$ hour in advance. e.g. nationwide schools can be started at 7 AM instead of 8 and offices and banks could be started at 9 AM instead of 10. e.g. Similar arrangement is done in Chai Bagan which is one hour ahead of IST informally. In 2014 the government-appointed committee led by scientist Dr. K. Kasturirangan had given its report by saying that benefit of second time zone does exist but operational and safety challenges especially for railways outweighed the gains. Thus he recommended retaining a single time zone while allowing flexible working hours.

Geomorphology

• Earth's interior
• Continental Drift theory
• Plate Tectonics theory
• Volcanic
• Earthquake
• Mountains, Plateaus, Plains
• Weathering and Erosion
• Rock and Rock cycle
• Landforms by
  • Rivers
  • Winds
  • Glaciers
  • Ground Water
  • Coastal waves

Earth's Interior

According to the various theories explaining origin of solar system and planets the Earth also came out from the same nebula which had formed our solar sun. The important theories include

1. Nebular Hypothesis: It is most accepted hypothesis today it was given Immanuel Kant in 1755. It was later developed by Laplace in 1796. Its main idea is that the solar system was formed from a rotating cloud of gases and dust called Nebula. The gravity caused the centre of nebula to collapse. It formed sun at the centre and the remaining materials formed planets.
2. Planetesimal Hypothesis: It was proposed by Chamberlin in 1905.
3. Tidal Hypothesis: It was given by James Jeans and Jeffreys in 1917.
4. Binary star Hypothesis: It was given by Russell.
5. Dust Cloud Hypothesis: It was given by Gerard Kuiper. If we consider any of these hypotheses as correct, and knowing that the Earth was formed 4.5 billion years ago as a hot semi-molten mass that later solidified, we might expect the Earth's surface to be a smooth, plain surface, but it is not so. The Earth's surface is highly irregular and full of relief features, mainly due to endogenic forces operating from the Earth's interior.

Study of Earth's Interior

The centre of earth which is called core has a depth 6370 km no technology can lead us to such depth to make direct observation. This is why scientists used both direct and indirect methods to understand the Earth's interior because the difficulty level to reach up to the core is too high to reach.

Direct Methods

1. Deep Mining:- Till date latest scientific tools and technology we have reached up to the depth of 8 to 12 km only. However, they suggest that with increasing depth temperature and density increase.
   • Study of temperature:- with increasing depth temperature increases by 1°C/32m but this rate of increase in temperature is restricted only up to 8km beyond that temperature increases but with relatively slower rate. That's why calculation suggest that at the depth of core temperature is about 5000 to 5500°C. Causes of such high temperature
     1. Trapped primordial heat from the formation of the Earth in its interior.
     2. Concentration of radioactive elements like Uranium and Thorium which decay and produce a high amount of heat. The maximum concentration of radioactive elements is in the upper mantle.
     3. Conversion of gravity into heat.
   • Study of Pressure:- with increasing depth pressure increases. Pressure is the force per unit area applied upon the lower surface by the overlying surface. This is why core bears maximum pressure followed by mantle followed by crust. To be more precise inner core maximum pressure followed by outer core, lower mantle, upper mantle, lower crust and upper crust. with increase in pressure
     • temperature increases with increasing depth
     • melting point of the rocks also increases. with increasing depth density of rocks gradually increases this is why their melting point is also high, e.g., the top most layer of the earth surface is made up of silica and aluminium that has least density the middle layer is made up of silica and magnesium whereas innermost part is made up of nickel and ferrous. Earth's surface rocks have an average density of 2.6g/cm³ to 3g/cm³ whereas core has 10-30g/cm³ this is why average density of 5.5g/cm³

Indirect methods

1. Study of Meteors Meteors help us in gaining direct observation. Meteors are rocks flying in space attracted by earth's gravity and hit the surface of earth as a solid mass. Meteors are the remnants of the past which reveals the process of formation of solar system as well as earth. In 99% cases these meteors are made up of iron and nickel which gives clear indication that the Earth's core should also be made up of iron and nickel.
2. Study of Volcanism Volcanic eruption is eruption of molten rocks from the interior with burst which clearly suggests that in the Earth's interior temperature, pressure and density all three increases with increasing depth

3. Study of Seismic waves Seismic waves are most effective method to know about interior because this is the only method to pass through the entire interior of earth. Seismic waves are of two types:-
   1. Surface waves:- Surface waves originate from the epicentre and do not travel through the interior of the Earth. They travel only on the surface. These are of two types L waves and R waves
   2. Body waves:- Body waves originate from the focus and travel only through the interior. These are of two types:
      1. Primary waves or P waves Primary waves carry maximum energy and have maximum velocity and shortest wavelength. It can pass through solid, liquid and gaseous medium. It refracts when medium is changed.
      2. S waves S waves carry lesser amount of energy and velocity than the P and its wavelength is also longer than P. It can only travel through solid medium. It also refracts when medium is changed.

Structure of Earth Interior

The study of P and S waves suggest that the Earth's interior is not homogeneous medium it is heterogeneous. It is divided primarily into three layers, i.e., crust, mantle, and core.

1. Crust Further study suggest that the crust also has two layers, upper crust and lower crust. Upper crust is further divided into two parts
   1. Oceanic Crust:- It has thickness of 0-10km. It is primarily made up of basalt.
   2. Continental Crust:- Continental crust has thickness of 35-40km. It is primarily made up of granite. upper crust is separated from the lower crust by Conrad discontinuity.
2. Mantle Mantle has two parts
   1. Upper Mantle:- Upper mantle is separated from lower crust by Mohorovičić discontinuity. It is also called asthenosphere.
   2. Lower Mantle:- Lower mantle is separated from upper mantle by Repetti discontinuity. It extends up to depth of 2900 km.
3. Core Core is divided into two parts
   1. Outer core:- It is in liquid state. It extends from 2900km to 5150km. This layer is responsible for the electromagnetic shield of the earth. It is separated from lower mantle by Gutenberg discontinuity.
   2. Inner Core:- Inner core is in solid state. It extends between 5150km to 6370km.

Geomagnetism

Geomagnetism refers to Earth's magnetic field, which makes the earth behave like a giant bar magnet with magnetic north and south poles. The magnetic axis is inclined by about 11° to the earth's rotation axis. This magnetic field extend into space forming the magnetosphere which surrounds and protects earth.

Causes of Geomagnetism

The earth's magnetic field is generated by geodynamic mechanism operating in the liquid outer core

• The outer core consist mainly of molten iron and nickel.
• Convection currents caused by heat escaping from the core lead to the movement of these electrically conductive fluids.
• Combined with the Earth's rotation, Coriolis force, these motions generate electric currents.
• The electric current in turn produces earth's magnetic field.

Impact of Geomagnetism

• Protection from solar radiation.
• Deflects charged particles from the sun, preventing harmful radiation from reaching the earth surface.
• Formation of Auroras:- Interaction between solar winds and magnetic field produces auroras near polar regions.
• Geomagnetic Storms:- Strong solar activity can disturb the magnetic field affecting satellite, ISS, communication system, GPS and power grids.
• Magnetic Navigation:- Compasses aligned with earth's magnetic field and aid navigation.

Importance of Geomagnetism

• Essential for the existence and evolution of life by shielding earth from solar and cosmic radiation.
• Helps in navigation of ships, aircraft, migratory birds like Amur Falcon which flies from Mongolia, Southern Siberia, Northern China to South Africa, Zimbabwe, Namibia and Botswana via India, Nagaland where it rests for a few weeks or months. Similarly, Siberian birds coming from Siberia to Bharatpur of Rajasthan.
• It provides clues about the earth's interior and core dynamics.
• It support space weather forecasting and satellite operations.

Recent Development

• Scientists continue to monitor the weakening and shifting of the magnetic field particularly the South Atlantic anomaly where magnetic intensity is usually low.
• European Space Agency's Swarm satellites to study changes in earth's magnetic field to improve understanding of the earth's interior core process and space weather.

Conclusion

Geomagnetism is dynamic phenomenon generated by the Earth's liquid outer core beyond enabling navigation, it acts as a protective shield against harmful solar radiation and provide critical insights into the Earth's interior.

Auroras

Auroras are spectacular natural light occurs in the upper atmosphere, ionosphere near the polar regions. These are known as aurora borealis in the northern hemisphere. These are also called northern lights. In southern hemisphere these are called aurora australis or southern lights.

Causes of Auroras

Auroras result from the interaction between the solar winds and earth's magnetic field

• The sun continuously emits charged particles called the solar winds.
• The earth's magnetosphere channels these particles towards the polar regions.
• The particles collide with gases in the upper most atmosphere mainly between the altitude of 80-400km i.e. ionosphere.
• There is presence of oxygen and nitrogen gases which become excited due to this interaction and release energy in the form of visible light.

Colours of Auroras

1. Green Colour:- It is mainly due to the presence of oxygen between 100-300km. It is most common colour.
2. Red Colour:- It is because of oxygen between 300-400km.
3. Blue and Purple Colour:- It is because of Nitrogen.

Importance of Auroras

1. Indicator of space weather:- Auroras helps scientists to monitor solar activity and geomagnetic storm.
2. Evidence of earth-sun interaction:- Demonstrate the functioning of the earth's magnetic field and magnetosphere.
3. Scientific Significance:- Provide insights into atmospheric physics, plasma dynamics and solar terrestrial relation.
4. Importance for technology:- Aurora event often accompany geomagnetic storms that can affect satellites, ISS, GPS, radio communication, power transmission, etc.
5. Economic and tourism value:- Auroras attract millions of tourists to the countries of north like Canada, Norway, Iceland, Finland to watch northern lights specially in the months of November to February. In the southern hemisphere, tourists visit Chile, Argentina, New Zealand, etc. in the months of May to August.

Conclusion

Auroras are visible manifestation of interaction between sun and earth. Beyond this scenic beauty they provide valuable information about space weather, geomagnetism and other atmospheric processes, making them important for both scientific and technological preparedness.

Continental Drift Theory

This theory was given by German Meteorologist named Alfred Wegener in 1912 and elaborated it in his book the 'Origin of continents and Oceans' in 1915. The theory states that the present continents were once joined together as a single super continent called Pangea, which later broke apart and drifted to their present positions. This theory was the first scientific attempt to explain the similarity of coastlines, rocks, fossils and geological structures found on different continents.

Concept of Continental Drift Theory

According to Wegener:-

• Around 250 million years ago, all land masses formed one giant supercontinent called Pangea.
• Pangea was surrounded by a super ocean called Panthalassa.
• A shallow sea was formed when Pangea was divided into two parts. The northern part of Pangea, situated north of the Tethys Sea, was called Laurasia, and the southern part was called Gondwanaland. The northern part is also known as Angaraland.
• Further rupturing of Laurasia formed North America and Eurasia.
• Further rupturing of Gondwanaland formed South America, Africa, Antarctica, India, Australia and Madagascar.
• Because of rupturing of the continents and their respective movement formed different oceans also like:-
  • Between North America and Eurasia intrusion of Panthalassa water formed North Atlantic and later on South Atlantic was formed between America and Africa.
  • Indian ocean was formed between Africa, Australia and Antarctica.
  • Arctic Ocean was formed when the Panthalassa water near North pole was surrounded by North America and Eurasia almost from all the sides.
  • Pacific ocean i.e. largest ocean on the planet is remnant of the old Panthalassa.
• Over geological time due to fragmentation of the land masses and their gradual shift has led to the present arrangement of the continents.
• Wegener believed that the continents are composed of lighter rocks i.e. silica and aluminium, floating over dense oceanic crust which is made up of silica and magnesium allowing them to move.

Evidence supporting this theory

1. Jigsaw fit of continents:- The coastlines of continents appear to fit together like pieces of a puzzle. e.g. the eastern coast of Brazil/South America matches closely with the western coast of South Africa. The best fit is obtained by matching continental shelves rather than present coastline. This suggested that these 2 continents were once joined.
2. Geological Evidence:- Rock formation and mountain belts of similar age and composition are found on opposite sides of the ocean e.g. the Pre-Cambrian rock formations occur in Africa and South America. These similarities indicate a common geological stream Similarly the Appalachian mountain of North America continue into Norway also a part of Caledonian mountain range. It suggests that these mountains were formed when North America and western Europe were together.
3. Fossil Evidence:- Identical fossils are found on continents now separated by oceans. e.g.
   1. Mesosaurus:- Fossil of Mesosaurus are found in South America. It was a fresh water reptile. It could not have crossed the Atlantic ocean.
   2. Lystrosaurus and Cynognathus:- Their fossils are found across multiple southern continents. Though these were land reptiles and unable to swim.
   3. Glossopteris:- It is fossil of a plant/fern found in India, Australia, Antarctica, Africa and South America. However, this plant grows in cold climatic conditions. Such fossil distribution strongly suggest that these continents were once connected.
4. Paleoclimatic Evidence:- Evidence of ancient climates also support continental drift. e.g. Permo-Carboniferous glacial deposits are found in India, South Africa, Australia, South America and Antarctica. These regions are now widely separated but once were part of Gondwanaland near the south pole. Other examples include the presence of vast coal deposits in Russia, Kazakhstan, US, UK (near Atlantic region) and in Antarctica. Coal forms in warm humid conditions indicating these areas were once located in different climatic zones.
5. Presence of Gold Placer Deposits near Guinea coast of Africa:- Many rivers carry gold deposits/minerals and deposit them into the sea but gold reserves are not found along with West African coast instead these are found in Brazil. If we put jigsaw fit evidence and the presence of gold placer deposits along with the fact that gold reserves are found in Brazil then it clearly becomes evident that these two continents were together in their geological past.

Forces Responsible for Continental Drift

Three types of forces were suggested by Wegener which were responsible for:-

1. Rupturing of Pangea
2. Movement of continents from pole to equator
3. Movement of continents to the west like North America and South America For rupturing of Pangea he made tussle between the gravitation and force of buoyancy.

• According to him since these two forces act in the opposite direction and gravity is more powerful force thus Pangea ruptured about 200 million years ago.
• Pole-fleeing Force:- It is caused by earth's rotation it is basically centrifugal force due to which continents were believed to move from the pole to equator like India, Africa, Eurasia, etc.
• Tidal Force:- It is generated by gravitational attraction of sun and moon which rise in the east and set down in west because of the earth rotates from west to east.

Limitations of Continental Drift Theory

1. Inadequate explanation of driving force:- The theory could not explain that
   1. Why Pangea ruptured:- According to Wegener, it was because of tussle between the gravity and force of buoyancy but scientists have proved that it was a wrong interpretation. Gravity keeps the things intact.
   2. Pole-fleeing force was held responsible for continental drift from poles toward equator:- Scientists have proved that not only this force is too weak to move the continents but also it should also move the mass i.e. both continent and ocean floor instead of continents only as suggested by Wegener.
   3. The tidal force of sun and moon:- Which were made responsible for the westward drift of the continent if taken seriously then this force should be 90,000 times greater than the present tidal forces of sun and moon and in such case it could have stopped the rotation of earth itself.
2. Apart from these limitations related to insufficiency of force he also lacked some conceptual clarity also e.g.
   1. According to him continents were drifting over the ocean floors this is conceptually wrong as plate tectonics has proved that it is lithospheric slabs that are drifting over the asthenosphere.
   2. Secondly, he tried to explain the formation of folded mountains and island arcs or archipelago. To explain these he said that when continents were drifting over ocean floor where frictional resistance along their leading margin that's why continents got folded and mountains were formed. Island arcs are those continental part found at trailing margin of the continents which could not match the rate of the drift of the moving continents e.g. Japan, Indonesia, Caribbean Island.

Conclusion

Alfred Wegener's continental drift theory was a landmark contribution to geology. Although it failed to explain the exact mechanism of continental movement, its extensive geological, fossil, and climatic evidence strongly suggested that the continents were once united as Pangea. Later discoveries in sea floor spreading and plate tectonics confirmed the essence of Wegener's idea, making the continental drift theory the foundation of modern geoscience and our understanding of the Earth's dynamic nature.

Plate Tectonics Theory

Types of Plates

• On the basis of their constituents
  1. Continental Plate
  2. Oceanic Plate
  3. Oceanic cum Continental Plate
• On the basis of their size
  1. 7 Major Plates are
     • North American Plate
     • South American Plate
     • African Plate
     • European Plate
     • Indo-Australian Plate
     • Antarctic Plate
     • Pacific Plate
  2. 20+ Minor Plates
     • Juan de Fuca
     • Cocos Plate
     • Caribbean Plate
     • Nazca Plate
     • Scotia Plate
     • Somalian Plate
     • Arabian Plate
     • Turkish Plate
     • Burma Plate
     • Philippine Plate
     • Bismarck Plate

Distribution of Plates

Plate Margin

There are three types of plate margins

1. Constructive Plate Margin It is formed when two plates move apart due to divergence. Two convection currents operating beneath the lithosphere in the asthenosphere; due to this: 1. Fissure eruption of volcano occurs 2. Mid oceanic ridges are formed e.g. MOR of Atlantic 3. Earthquakes of mild magnitude occur

2. Conservative Plate Margin Conservative plate margins are those where two plates neither converge nor diverge. The two plates simply slide past each other, which is why there is no construction or destruction of crust. It only develops:
   1. Transform faults
   2. High Magnitude earthquakes
   3. No volcanism e.g. San Andreas fault of North America.

3. Destructive/Convergent Plate Margin A destructive plate margin or convergent plate boundary develops when two plates move towards each other; in this case, there are three possibilities:
   1. Continental and Oceanic Plate Convergence In this case
      • central eruption of volcanoes develop, e.g., Mt. Stromboli of Italy.
      • folded mountains are formed e.g. the Andes mountains were formed due to plate convergence between the South American plate and the Nazca plate.
      • high-magnitude earthquakess

   2. Oceanic and Oceanic Plate Convergence When two oceanic plates converge, the relatively heavier plate subducts under the lighter plate; due to this:
      • Island arcs are formed and sometimes festoons also.
      • Central eruption of volcanoes, e.g., Mt. Fuji of Japan, Mt. Mayon and Mount Taal in the Philippines, Mt. Krakatoa of Indonesia.
      • High Magnitude earthquakes and Tsunami e.g. the 2004 tsunami was near Indonesia, 2011 tsunami was due to Japan
   3. Continental and Continental Plate Convergence When two continental plates converge, the relatively heavier plate subducts beneath the lighter plate due to this
      • High mountain ranges are formed, e.g., the Himalayas.
      • No volcanic eruption because
        • Thickness of the lithosphere becomes almost double due to subduction / under thrusting
        • Due to lack of water steam support to rising magma is very weak.
        • Rising magma is very viscous.
      • High-magnitude earthquakes.

An island arc is Curved chain of volcanic islands formed at a convergent plate boundary where one oceanic subducts beneath another oceanic plate. The subducted plate melts in the mantle magma rises through cracks. Repeated volcanic eruptions form a chain of islands parallel to the ocean trenches; due to Earth's curvature and plate movement, the chain generally develops a crescent or arc shape. e.g. Japan, Philippines, Indonesia, etc. Festoons are highly curved, chain-like curved arcs that represent the most pronounced form of island arcs, resembling a garland or necklace. They are formed by intense subduction and strong compressional forces. The differential plate movement causes the arc to bend more sharply. These are often associated with deep ocean trenches and active volcanoes. Indonesia and the Philippines are examples of island arcs and festoons.

• Indonesia

• Indonesia is located where several plates meet such as the Indo-Australian Plate, Eurasian plate, the Pacific Plate and the Philippine Plate.

• Formation Process of Indonesia

  Stage 1- Subduction of Indo-Australian Plate: The oceanic part of the Indo-Australian plate moves northward. It subducts beneath the Eurasian plate Stage 2 - Formation of Ocean Trenches e.g. Java Trench and Sunda Trench Stage 3 - Magma generation: Subduction of the plate in the asthenosphere leads to its melting and formation of magma Stage 4 - Development of Volcanic arc: Magma rose to the surface and formed Volcanic islands like Sumatra, Java, Bali, Lombok, etc. Indonesia is the world's largest archipelago. It has about 17,000+ islands, over 120 active volcanoes and experiences frequent earthquakes and tsunami due to active subduction.

• Formation Process of Philippines

  Philippines lies at the junction of Philippine plate, Eurasian plate and Sunda plate Stage 1 - Oceanic plate convergence: The The Philippine Sea plate and parts of the Eurasian plate moved toward each other. One heavier oceanic plate began subducting beneath the other. Stage 2 - Formation of deep Trenches: Subduction created deep ocean trenches such as Mariana trench, Mindanao trench. Stage 3 - Magma Generation: The descending plate released water into mantle partial melting occurred. Magma rose through volcanoes. Stage 4 - Volcanic Islands are formed: These islands merge and grew into larger islands such as Luzon. Philippines has more than 7000 island and numerous active volcanoeses.

Force responsible for plate Tectonics

According to geoscientists, the most important force responsible for plate movement is the flow of convection currents operating in the asthenosphere. These convection currents are formed due to the decay of radioactive elements, which produces a huge amount of heat and melts the surrounding rock. These molten rocks form convection currents. When two convection cells converge or diverge, the overlying plates converge or diverge, respectively. There are two secondary forces also responsible for plate movement:

1. Ridge push force: This force is applied by the magma rising through the divergent plate boundary
2. Slab Pull: When a subducting plate enters into asthenosphere it pulls rest of the plate inside.

Evidence of Plate Tectonics Theory

Evidence of Plate Tectonics Theory include:

1. Sea Floor spreading
2. Palaeomagnetism
3. Hot spots (Volcanos)

Sea Floor Spreading and its support to Plate Tectonics Theory

The idea of sea floor spreading refers to the process by which new oceanic crust is formed at mid oceanic ridges and gradually moves away on either side. The concept was proposed by Harry Hess in the 1960s and became a crucial foundation for the theory of plate tectonics. According to this theory, molten magma rises from the mantle through fissures at divergent plate boundaries, especially along mid oceanic ridges such as mid Atlantic ridge. As the magma cools and solidifies, it forms new basaltic crust. Continuous addition of new material pushes the older crust away from the ridge, causing the ocean floor to spread.

Mechanism of sea floor spreading

• Upwelling of magma occurs due to convection currents in the mantle.
• New oceanic crust is created at the mid oceanic ridge.
• Older crust moves outward symmetrically.
• Oceanic crust is eventually destroyed at subduction zones or ocean trenches.

Evidence supporting Sea floor Spreading.

1. Age of Oceanic Crust:- Rocks near the mid-oceanic ridges are younger while those farther away are older.
   It clearly suggests that gradual spreading of the sea floor is a reality.
2. Thickness of Sediments:- Marine sediments are thinner near mid-oceanic ridge and thicker away from them because older crust has had more time to accumulate sediments.

3. Palaeomagnetism:- Alternating magnetic bands on either side of ocean ridges record periodic reversals in earth's magnetic field. The symmetrical arrangement proves continuous creation and outward movement of oceanic crust.