Category : UPSC






Astronomy is a science that asks fundamental questions about the very basic of things, the universe. The Universe is all of time and space and its contents. The Universe includes planets, stars galaxies, the contents of intergalactic space, the smallest subatomic particles, and all matter and energy. The observable universe is about 28 billion parsecs (91 billion light-years) in diameter at the time. The size of the whole Universe is not known and may be either finite or infinite. Observations and the development of physical theories have led to inferences about the composition and evolution of the universe.





·                     Everything that exists, from the Galactic Megaclusters to the tiniest subatomic particles, comprises the Universe

·                     As for the age of Universe, scientists agree that it is about 13.82 billion years old.

·                     The universe comprises of a number of galaxies.

·                     Optical and radio telescope studies indicate the existence of between 100-200 billion galaxies in the visible universe

·                     The Big Bang Theory is most accepted for the origin of Universe in comparison to the steady state and the Pulsating




·                     Galaxy is a collection of millions or billions of stars and planets that are held together by gravitational pull.

·                     Milky Way is one such galaxy. The earth lies in this galaxy. It is called Milky Way, because it looks like a river of milky light flowing from one corner to another of the sky.

·                     It is spiral in shape.

·                     We call it Akash Ganga

·                     The nearest galaxy to Milky Way is Andromeda. Andromeda is a spiral galaxy and approximately 2.5 million light-years from the earth.

·                     Andromeda is also known as NGC224 and M31



·                     Luminous heavenly bodies which have their own light and other radiant energy are called star.

·                     They are made of extremely hot burning gases. Star looks - Red with low temperature, Yellow with higher and blue with very high temperature.


Star (Birth to Death)


·                     Star starts its life as clouds of dust and gas known as Nebula.

·                     The gaseous matter of Nebula further contracts to make dense region named Proto Star.

·                     The Proto Star further condenses to a critical stage of mass where nuclear fusion begins and star finally comes into existence.

·                     When all the hydrogen?s of a star are used up then its helium begins fusing into carbon. At a stage helium's fusion and energy production inside the star stops. As a result stars core contracts under its own weight to a very high density to make a white Dwarf star.

·                     White Dwarf star becomes dark balls of matter on cooling to make Black Dwarf Star,

·                     The mass of white Dwarf Star is less than 1.44 times the mass of the Sun named as Chandrasekhar Limiting Mass.

·                     White Dwarf Star is a dead star because of the end of fusion reaction and energy production.

·                     It shines by radiating its stored heat.

·                     Giant star expands into Red Supergiant after consuming its fuel (H & He). At a stage, it explodes as Supernova or changes into Neutron or Black Holes.

·                     The nearest star to the Earth is the Sun followed by Proxima and Alpha Centauri and radiant energy. (4.35 light years)




·                     A Constellation is a group of stars that makes an imaginary shape in the sky at night.

·                     It helps in navigation of sea vessel during night as they are seen in a fixed direction at a particular period of time in a year.

·                     Orian, Big Dipper, Great Bear, Cassiopeia are some examples of constellations.

·                     Orion or Mriga can be seen in the late evening during winter;

·                     Cassiopeia in the Northern Sky is seen during winter.

·                     Great Bear consists of Ussa Minor (Laghu Saptarishi) and Ussa Major (Vrihat Saptarishi), and can be seen in early night during summer.




·                     It is a star made up of extremely hot gases, particularly by hydrogen (71%), Helium (27.1%) and others (1.9%) gases.

·                     Its diameter 109 times bigger than the earth and weighs 2 x 1027 tonnes, and accounts for 99.83% of mass of the solar system.

·                     It is 149.6 million km away from the earth. The sun light takes 8 minutes to reach the earth's surface.

·                     It has immense gravitational pull which keeps the planets fixed in their orbit, revolving round the sun.

·                     It continuously gives off energy in the form of visible light, infra red, ultra violet, X-rays, gamma rays, radio waves and plasma gas.

·                     The period of revolution of the sun around the galactic centre is 250 million year. This period is called as cosmic or galactic year.

·                     Sudden flash of brightness observed near the sun?s surface which is a collection of magnetic energy including electrons, protons and nuclei is called as solar flares. They are consized particles and are harmful for satellite communication.

·                     The layers of sun are divided according to their brightness level which is represented in the write features of each layer shown in the figure.



·                     The core of the sun consists of hydrogen atoms which fuse together due to compression and creates helium. This is called as nuclear fusion.

·                     Nuclear fusion produces huge amount of energy. It is radiated outward to the surface, atmosphere and beyond.

·                     Convection zone is the next to the core of the sun. Here the temperature drops to 2 million degree C.

·                     Photosphere?s temperature is \[6,{{000}^{{}^\circ }}\]C.

·                     Atmosphere of the sun consists of chromosphere and corona.

·                     Corona is seen in a form of spectral lines emitted by iron, calcium and nickel ions. lonization of these elements increases temperature of corona.

·                     Recently coronal heating puzzle has been related to magnetic carpet found in corona.

·                     The solar flare (wind) is a stream of charged particles released from upper atmosphere of the sun. These changed particles when get trapped by earth's magnetic field while entering in the upper atmosphere of the earth results in auroral (light) display.

·                     These auroral display in the northern hemisphere is called as Aurora Borealis (the Northern light) and when occurs in southern hemisphere is called as Aurora Australis (the Southern lights)

·                     Sun-spots are dark appearing areas present in photosphere from where solar flares originate. They are relatively a region cooler than its surrounding. It appears and disappears after every 11 years. This period is called Sun-spot Cycle.

·                     Plage is a brighter region in the chromosphere near to sunspot.




·                     Planets means 'wanderers'. There are eight planets in our solar system (Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune).

·                     All these planets move around the sun in a fix orbit. Which is elongated in shape (elliptical).

·                     A new planet 2003 UB 313 has been included recently in solar system. It is bigger than Pluto and farthest from the Sun.

·                     International Astronomical Union (IAU) recognized five dwarf planets such as: Ceres, Pluto, Haumea, Makemake, and Seden.

·                     The planets are grouped into two :

(1) Terrestrial planets: These are dense rocky bodies and are called as earth like planets. Mercury, Venus, Earth, and Mars are included in it. They are also called as inner planets.

 (2) Jovian Planets: The outer planets which are gigantic in size and are gaseous in composition with large satellite are called as Jovian planets. These have similar features to that of Jupiter, thus called as Jupiter like planets.


Pluto, the Dwarf Planet

·                     Pluto was known as the smallest planet in the solar system and the ninth planet from the sun.

·                     Today Pluto is called a "dwarf planet".

·                     On owerage, Pluto is more than 3.6 billion miles away from the sun.

·                     Pluto is in a region called the kwpes Belt. One day on Pluto is about 61/2 days on Earth.

·                     It has five moons. Its largest moon is named Charon pluto?s four other moons are named kerberos, styx, Nix and Hydra.

Detail information about the planets











Equatorial & Diameter (km)










Mass (Kg)

\[3.28\times {{10}^{23}}\]

\[4.867\times {{10}^{24}}\]

\[5.972\times {{10}^{24}}\]

\[6.39\times {{10}^{23}}\]

\[1.8913\times {{10}^{27}}\]

\[5.683\times {{10}^{26}}\]

\[8.681\times {{10}^{25}}\]

\[1.024\times {{10}^{26}}\]

Orbital Period (in days)










Inclination to Sun?s Equator









Rotational Period (in days) and Direction

58.64 East to West

- 243.02

West to East


1 East to West

1.03 East to West

0.41 East to West

0.43 East to West

- 0.72 West to East


0.67 East to West

Distance from Sun (km)

\[57.91\times {{10}^{6}}\]

\[10.82\times {{10}^{7}}\]

\[14.96\times {{10}^{7}}\]

\[22.79\times {{10}^{7}}\]

\[77.85\times {{10}^{7}}\]

\[14.33\times {{10}^{8}}\]

\[28.77\times {{10}^{8}}\]

\[44.98\times {{10}^{8}}\]










No. of Moons









Axis Tilt









Mean density\[(g/c{{m}^{3}})\]






















·                     Mercury is the smallest planet in our solar system ? only slightly larger than the Earth's moon.

·                     It is the closest planet to the sun at a distance of about 58 million km (36 million miles) or 0.39 AU.

·                     One day on Mercury takes 59 Earth days.

·                     Mercury is a rocky planet, also known as a terrestrial planet.

·                     Mercury?s thin atmosphere, or exosphere, is composed mostly of oxygen \[({{O}_{2}})\] sodium (Na), hydrogen \[({{H}_{2}})\] helium (He), and potassium (K). Atoms that are blasted off the surface by the solar wind and micrometeoroid impacts create Mercury?s exosphere.

·                     Only two missions have visited this rocky planet: Mariner 10 in 1974-5 and MESSENGER, which flew past Mercury three times before going into orbit around Mercury in 2011.

·                      Daytime Temperatures can reach \[{{430}^{0}}\] Celsius (\[{{800}^{0}}\] Fahrenheit) and drop to -\[{{180}^{0}}\] Celsius (-\[{{290}^{0}}\] Fahrenheit) at night.




·                     Venus is only a little smaller than the Earth.

·                     Venus is the second closest planet to the sun at a distance of about 108 million km (67 million miles) or 0.72 AU.

·                     One day on Venus lasts as long as 243 Earth days (the time it takes for Venus to rotate or spin once).

·                     Venus is a rocky planet, also known as terrestrial planet, Venus? solid surface is a created and volcanic landscape.

·                     Venus' thick and toxic atmosphere is made up mostly of carbon dioxide \[(C{{O}_{2}})\] and nitrogen \[({{N}_{2}})\] with clouds of sulfuric acid \[({{H}_{2}}S{{O}_{4}})\]droplets.

·                     More than 40 spacecraft have explored Venus. The Magellan mission in the early 1990s mapped 98% of the planet's surface.

·                     The planet's extreme high temperatures of almost \[480{}^\circ \] Celsius (\[900{}^\circ \] Fahrenheit) made it seem an unlikely place for life as we know it.

·                     Venus spins backwards (retrograde rotation) when compared to the other planets. This means that the sun rises in the west and sets in the east on Venus.




·                     Earth is the third planet from the sun at a distance of about 150 million km (93 million miles). That's one Astronomical Unit (AU).

·                     A day on Earth is 24 hours (the time it takes the Earth to rotate or spin once).

·                     Earth's atmosphere is 78% nitrogen (N3), 21% oxygen \[({{O}_{2}})\]and 1% other ingredients - the perfect balance for Earthlings to breathe and live. Many planets in our solar system have atmospheres, but only Earth is breathable.

·                     Earth has one moon. Another name for a moon is natural satellite.

·                     Earth is the perfect place for life as we know it.

·                     Our atmosphere protects us from incoming meteoroids, most of which break up in our atmosphere before they can strike the surface as meteorites.




·                     Mars is the fourth planet from the sun at a distance of about 228 million km (142 million miles) or 1.52 AU.

·                     One day on Mars takes just a little over 24 hours (the time it takes for Mars to rotate or spin once).

·                     Mars is a rocky planet, also known as a terrestrial planet. Mars' solid surface has been altered by volcanoes, impacts, crustal movement and movement and atmospheric effects such as dust storms.

·                     Mars has a thin atmosphere made up mostly of carbon dioxide \[(C{{O}_{2}})\]nitrogen\[({{N}_{2}})\]and argon (Ar).

·                     Mars has two moons named Phobos and Deimos.

·                     Several missions have visited this planet, from flybys and orbiters to rovers on the surface of the Red Planet. The first true Mars mission success was Mariner 4 in 1965. At this time in the planet?s history, Mars' surface cannot support life as we know it. Current missions exploring Mars on the surface and from orbit are determining Mars? past and future potential for life.

·                     Mars is known as the Red Planet because iron minerals in the Martian soil oxidize, or rust, causing the soil and the dusty atmosphere to look red.




·                     About 1,300 Earths could fit inside Jupiter.

·                     Jupiter is the fifth planet from the sun at a distance of about 778 million km (484 million miles) or 5.2 Astronomical Units (AU). Earth is one AU from the sun.

·                     One day on Jupiter takes about 10 hours (the time it takes for Jupiter to rotate or spin once).

·                     Jupiter is a gas-giant planet and therefore does not have a solid surface. Jupiter may have a solid, inner core about the size of the Earth.

·                     Jupiter?s atmosphere is made up mostly of hydrogen \[({{H}_{2}})\] and helium (He).

·                     Jupiter has 50 known moons, with an additional 17 moons awaiting confirmation of their discovery that is a total of 67 moons.

·                     Jupiter has a faint ring system that was discovered in 1979 by the Voyager-1 mission. All four giant planets in our solar system have ring systems.

·                     Many missions have visited Jupiter and its system of moons. The Juno mission will arrive at Jupiter in 2016.

·                     Jupiter cannot support life as we know it. However, some of Jupiter's moons have oceans underneath their crusts that might support life.




·                     Saturn is the sixth planet from the sun at a distance of about 1.4 billion km (886 million miles) or 9.5 AU.

·                     One day on Saturn takes 10.7 hours (the time it takes for Saturn to rotate or spin once).

·                     Saturn is a gas-giant planet and therefore does not have a solid surface.

·                     Saturn?s atmosphere is made up mostly of hydrogen \[({{H}_{2}})\]and helium (He).

·                     Saturn has 53 known moons with an additional nine moons awaiting confirmation of their discovery that is a total of 62 moons.

·                     Only a few missions have visited Saturn: Pioneer 11, Voyager 1 and 2 and Cassini-Huygens. Since 2004, Cassini has been exploring Saturn, its moons and rings.

·                     Fact: When Galileo Galilei was observing the planet Saturn in the 1600s, he noticed strange objects on each side of the planet and drew in his notes a triple-bodied planet system and later a planet with arms or handles. These ?handles? were in fact the rings of Saturn.




·                     Uranus is the seventh planet from the sun at a distance of about 2.9 billion km (1.8 billion miles) or 19.19AU.

·                     One day on Uranus takes about 17 hours (the time it takes for Uranus to rotate or spin once).

·                     Uranus is an ice giant. Most (80 % or more) of the planet?s mass is made up of a hot dense fluid of ?icy? materials ? water \[({{H}_{2}}O)\] methane \[(C{{H}_{4}})\] and ammonia \[(N{{H}_{3}})\]-above a small rocky core.

·                     Uranus has an atmosphere which is mostly made up of hydrogen \[({{H}_{2}})\] and helium (He), with a small amount of methane \[(C{{H}_{4}})\]

·                     Uranus has 27 moons. Uranus' moons are named after characters from the works of William Shakespeare and Alexander Pope.

·                     Voyager 2 is the only spacecraft to have visited Uranus. Uranus cannot support life as we know it.

·                     Unlike any of the other planets, Uranus rotates on its side, which means it spins horizontally.








·                     Neptune is the eighth and farthest planet from the sun at a distance of about 4.5 billion km (2.8 billion miles) or 30.07 AU.

·                     One day on Neptune takes about 16 hours (the time it takes for Neptune to rotate or spin once).

·                     Neptune is a sister ice giant to Uranus.

·                     Neptune?s atmosphere is made up mostly of hydrogen \[({{H}_{2}})\] helium (He) and methane \[(C{{H}_{4}})\]

·                     Neptune has 13 moons. Neptune's moons are named after various sea gods and nymphs in Greek mythology.

·                     Neptune has six rings.

·                     Voyager 2 is the only spacecraft to have visited Neptune.




·                     The moon is Earth?s natural satellite and orbits the Earth at a distance of about 384 thousand km (239 thousand miles) or 0.00257 AU.

·                     The moon makes a complete orbit around Earth in 27 Earth days and rotates or spins at that same rate, or in that same amount of time. This causes the moon to keep the same side or face towards Earth during the course of its orbit.                                            

·                     The moon is a rocky, solid-surface body, with much of its surface cratered and pitted from impacts. The moon has a very thin and tenuous (weak) atmosphere, called an exosphere.

·                     More than 100 spacecraft?s have been launched to explore the moon. It is the only celestial body beyond Earth that has been visited by human beings. Twelve human beings have walked on the surface of the moon.




·                     Asteroids are minor planets especially those of the inner solar system.

·                     Asteroids orbit our sun in a region of space between the orbits of Mars and Jupiter known as the Asteroid Belt.

·                     Asteroids are solid, rocky and irregular bodies.

·                     Asteroids do not have atmospheres.

·                     More than 150 asteroids are known to have a small companion moop (some have two moons). The first discovery of an asteroid-moon system was of asteroid Ida and its moon Dactyl in 1993.

·                     Asteroids do not have rings.

·                     NASA space missions have flown by and observed asteroids, and one spacecraft (NEAR Shoemaker) even landed on an asteroid (Eros). The Dawn mission is the first mission to orbit (2011) a main belt asteroid (Vesta).

·                     Ceres, the first and largest asteroid to be discovered (1801) by Giuseppe Piazzi), encompasses over one-third of the estimated total mass of all the asteroids in the asteroid belt.




·                     Meteorites may vary in size from tiny grains to large boulders. One of the largest meteorite found on Earth is the Hoba meteorite from southwest Africa, which weighs roughly 54,000 kg (119,000 pounds).

·                     Meteor showers are usually named after a star or constellation which is close to the radiant. Meteors and meteorites begin as meteoroids, which are little chunks of rock and debris in space.

·                     Most meteorites are either iron, stony or stony-iron.

·                     Leonid MAC (an airborne mission that took flight during the years 1998 - 2002) studied the interaction of meteoroids with the Earth's atmosphere.

·                     Meteoroids, meteors and meteorites cannot support life. However, they may have provided the Earth with a source of amino acids: the building blocks of life.

·                     Meteoroids become meteors or shooting stars when they interact with a planet's atmosphere and cause a streak of light in the sky. Debris that makes it to the surface of a planet from meteoroids are called meteorites.

·                     Meteorites may look very much like Earth rock, or they may have a Durnea appeal (thumbprint-like), roughened or smooth exteriors.

·                     Many of the meteor showers are associated with comets. The Leonids are associated with comet Tempel-Tuttle; Aquarids and Orionids with comet Halley, and the Taurids with comet Encke.




·                     Comets are cosmic snowballs of frozen gases, rock and dust.

·                     A comet warms up as it comes near the sun and develops an atmosphere, or coma. The coma may be hundreds of thousands of kilometers in diameter.

·                     Comets do not have moons.

·                     Comets do not have rings.

·                     Several missions have visited, impacted and even collected samples from comets. Two recent missions are Stardust- NExT and Deep Impact EPOXI.

·                     When comets come around the sun, they leave a dusty tail. Every year the Earth passes through the comet tails, which allows the debris to enter our atmosphere where it burns up and creates fiery and colorful streaks (meteors) in the sky.

·                     Comets may not be able to support life themselves, but they may have brought water and organic compounds, i.e., the building blocks of life - through collisions with the Earth and other bodies in our solar system.

·                     Comet Halley makes an appearance in the Bayeux tapestry from the year 1066, which chronicles the overthrow of King Harold by William the Conqueror at the Battle of Hastings.

·                     It is a short period comet visible from Earth every 75-76 years. Halley last appeared in the inner part of the solar system in 1986 and will next appear in mid - 2061,


Who is Called What

Brightest Planet


Evening Star


Morning Star


Hottest Planet


Nearest Planet to Earth


Earth's twin


Fastest rotation in solar system


Slowest rotation in solar system


Green Planet


Blue Planet


Red Planet


Smallest Planet


Biggest Planet


Fastest revolution in Solar System


Slowest revolution in Solar System


Coldest Planet


Closest star to the Sun

Proxima Centauri

Densest Planet


Least dense Planet


Only satellite with an atmosphere like Earth


Smallest satellite


Biggest Satellite



Venus is the hottest planet even though Mercury is the closest planet to the Sun. The reason behind it is that Venus has atmosphere made of carbon dioxide.




The Earth is the only known planet where life exists. Its surface area is covered with two-third of water that is why we call it blue planet.

Earth is the third planet from the sun, the densest planet in the solar system, the largest of the solar system's four terrestrial planets.


Origin of the Earth


·                     A number of theories have been proposed by different philosophers.

·                     Immanuel Kant gave gaseous hypothesis based on Newtonian law related to gravitation and rotatory motion in 1755.

·                     Laplace gave Nebular hypothesis in 1786.

·                     Tidal hypothesis was given by James Jeans in 1929 and it was modified by Jeffrey and was called as Collision hypothesis.

·                     Big Bang theory was proposed by Georges Lemaitre (1927).

·                     According to Big Bang theory billion years ago cosmic matters were in highly compressed state. The expansion started with premordial explosion. It resulted in formation of superdensed balls which travelled at a speed of thousands mile per second and gave rise to galaxies.

·                     The expansion of universe means increase in space between galaxies and formation of new galaxies



Earth Statistice

 Age of The Earth

4.5 to 4.6 billion years

 Water-land Ratio

70.8% Water & 29.2 % Land

  Earth's Circumference at the Equator

24,901.55 miles (40,075.16 km)

 Earth's Circumference between the North and South poles  

 24,859.82 miles (40,008 km)

  Earth's Diameter at the Equator

 7,926.41 miles (12,756.32 km)

  Average Distance from the Earth to the Sun


92,9555,802 miles (149,579.870 km)

   Average Distance from the Earth to the Moon

238,855 miles (384,400.1 km)

    Highest Elevation on Earth

Mt. Everest, Asia : 29,035 feet (8848m)

   Tallest Mountain on Earth from Base to Peak


Mauna Kea. Hawaii: 33,480 feet, i.e10204 m (rising to 13796 feet above sea level (417m)

   Point Farthest from the Center of the Earth

The peak of the volcano Chimborazo in Ecoador at 20561 feet (6269m)is farthest from the center of the Earth due to its location near the equator and the oblateness of the Earth .

   Lowest Elevation on Land

Dead Sea: 1369 Feet Below sea level (417m)

  Deepest Point in the Ocean

Challenger Deep (Mariana Trench in Western Pacific Ocean: 36,740 feet (11022m)

   Highest Temperature Recorded

\[{{136.8}^{0}}\]F-AL Aziziyah, Libya, Sep. 13,1922(58.\[{{4}^{0}}\]C)

   Lowest Temperature Recorded

-128.\[{{6}^{0}}\]F-AL- Vostok, Antarction. July 21,1983(-89.\[{{2}^{0}}\]C )

  Atmosphere content

78% nitrogen, 21% oxygen and 1% traces of argon , carbon dioxide and Water.

   Rotation on Axis

23 hours and 56 minutes and 04.09053 second. But it takes an additional four minutes for the earth to revolve to the same  position as the day before relative to the sun (i.e.24 hours)

   Revolution Around Sun

365.2425 day

  Chemical Composition of the Earth

32.1% Iron,30.1% Oxygen,15.1% Silicon, 13.9%, Magnesium, 2.9% Sulfur, 1.8% Nickel, 1.5% Calcium and 2.6% other

   Standard Time zones


Size and Shape of the Earth


  • Shape of the Earth is called “geoid”
  • The sciences of earth measurement is called “Geodes
  • “ellipsoid” - reference to the Earth shape.



The geoid bulges at the North Pole and is depressed at the South Pole


  • Earth shape is affected by two main facts:
  • It bulges in midriff, because of pliability of Earth's lithosphere;
    • Its shape is therefore an oblate spheroid.
    • It has topographical irregularities.


Motions of the Earth


The Earth is constantly in motion, revolving around the Sun and rotating on its axis. These motions account for many of the phenomenon we see as normal occurrences: night and day, changing of the seasons, and different climates in different regions. With a globe ball properly mounted and rotating on its axis, the movements of the Earth around the Sun may be illustrated accurately.


The Earth spins on its axis from West to East (counter-clockwise). It takes the Earth 23 hours, 56 minutes, and 4.09 seconds to complete one full turn. Day and night are produced by the rotation of the Earth. The speed of rotation at any point upon the equator is at the rate of approximately 1,038 miles per hour, decreasing to zero at the poles.

·                     How rotation periods are calculated: The period of rotation is calculated with reference to a star and with reference to the sun. When it is calculated with reference to a star, it is called a sidereal day and when it is calculated with reference to the sun, it is called a solar day.

·                     Solar days and sidereal days: The solar day is a time period of 24 hours, and the duration of a sidereal day is 23 hours 56 minutes. This difference of four minutes between a solar day and a sidereal day is due to the fact that the position of the Earth keeps changing with reference to the sun due to the revolution around it; while with reference to a star at infinity, it will remain unchanged. Thus, a sidereal day is the actual time taken by the planet for a rotation of exactly 360 degrees on its axis.



While the Earth is spinning on its axis, it is revolving around the Sun in a counter-clockwise direction. It takes the Earth one full year to complete one full revolution around the Sun. This path is known as the Earth's orbit. It is very near a circle. The mean distance of the Earth from the Sun is about 93 milling miles and the distance varies by 3 million miles, forming a slightly oval path.

The revolution of the Earth around the Sun traverse a distance of 595 million miles in 365 days, 6 hours, 9 minutes and 9.5 seconds. This means a speed of 18 miles a second (or 66,000 miles per hour) while at the same time rotating once each twenty-four hours.



Earth rotates in an elliptical orbit around the Sun. The orbit of the Earth around the sun is elliptical and not circular. Due to this, the distance between the Earth and the sun keeps changing.

·                     When this distance is minimum, the Earth is said to be in perihelion (around January 3).

·                     When the distance is the maximum, it is said to be in aphelion (around July 4).

The Earth's axis points constantly to the same point (the polar star) in the celestial sphere. As a consequence the latitude on the surface of the earth at which the sun's rays fall vertically keeps changing as the earth moves it its orbit around the sun. Due to this the earth attains four critical positions with reference to the sun.


1.   The equinoxes: On 21st March, the Earth is     so positioned with reference to the sun that the sun's rays are vertical at the equator and the entire world experiences equal day and night.


2.   The autumnal equinox: A similar situation occurs on September 23.


3. Summer solstice: On 21st of June the sun?s rays are vertical over the Tropic of Cancer as the north pole of the Earth is inclined at its maximum towards the sun. At this time, the North Pole experiences a long continuous day and the South Pole a long continuous night (ergo, what we the summer season at this time and the southern hemisphere experiences winter now. Also the days are longer than the nights in the northern hemisphere at this time.


4. Winter solstice: On December 22, the position of the earth with respect to the sun is such that the South Pole is inclined at its maximum towards the sun and the Tropic of Cancer receives the vertical rays of the sun. This position is called the winter solstice when the sun shines continuously in the South Polar Region and it is a long continuous night at the North Pole. This is the winter season in the northern hemisphere and the summer in the southern hemisphere. During the winter solstice, the days are longer than the nights in the southern hemisphere.

·                     Thus, the variation in the duration of day and night and the change of seasons are due to the earth's revolution and the inclination of the axis of the earth. Also the seasons are reversed from the northern to the southern hemisphere.


Longitudes and Latitudes


Together, longitudes and latitudes form the Earth?s geographical coordinates, and represent the angular distance of any location on the Earth from the Earth's Equator. Both latitudes and longitudes are measured in degrees.



The Equator

The Earth is (almost, but not quite) a sphere that rotates around its axis. If we draw a line passing through the center of the Earth along its rotational axis, the line would pass through the North and the South Pole.

The Equator is an imaginary line perpendicular to this axis. It is equidistant from the two poles, and divides the globe into the Northern Hemisphere and the Southern Hemisphere. Most locations on the Equator experience consistently high temperatures throughout the year. They also experience almost 12 hours of daylight every day during the year. On the Equinoxes -50 autumnand spring - the sun is directly overhead the Equator, resulting in exactly 12 hour days and 12 hour nights.



  • Latitudes are imaginary circles drawn parallel to the They are defined by the angle created by a line connecting the latitude and the center of the Earth, and the line connecting the Equator and the center of the Earth, and are named by the angle. Latitudes specify the North-South position of a location on the globe.
  • When looking at a map, latitude lines run horizontally. Latitude lines are also known as parallels since they are parallel and are an equal distant from each other



  • Longitudes are geographical positioning markers that run from the geographical North to the geographical South Pole, intersecting the Equator. They meet at both Poles, and specify the East-West position of a location.
  • Longitudes are therefore imaginary circles that intersect the North and South Poles, and the Equator. Half of a longitudinal circle is known as a Meridians are perpendicular to every latitude.
  • Unlike, latitudes, there is no obvious central longitude. However, in order to measure the position of a location based on the longitude, cartographers and geographers over the course of history have designated different locations as the main longitudinal reference point. Today, the meridian line through Greenwich, England is considered as the reference point for longitudes. This line is also known as the Prime Meridian
  • The Prime Meridian is set as \[{{0}^{0}}\]longitude and it divides the Earth into the Eastern and the Western Hemisphere. All the other longitudes are measured, and named after the angle they make with respect to the center of the Earth from the intersection of the Meridian and the Equator.
  • Since a sphere has 360 degrees, the Earth is divided into 360 longitudes. The meridian right opposite the Prime Meridian (on the other side of the Earth) is the \[{{180}^{0}}\] longitude.
  • Modem timekeeping systems use longitudes as references to keep time. Time zones are defined by the Prime Meridian and the longitudes.


Time and Longitudes

Local Time

Local time of any place is 12 noon when the Sun is exactly overhead.

Standard Time

It is the uniform time fixed by each country. It is fixed in the relation to mean time of a certain meridian which generally passes through it.

Greenwich Mean Time (GMT)                          

The line at \[{{0}^{0}}\] longitude is called Greenwich Mean Time. It is based on local time of the meridian passing through Greenwich near London.


Indian Standard Time

It is fixed on the mean of \[{{82}^{0}}{{30}^{0}}\]E. Meridian, a place near Allahabad. It is 5’/2 hours ahead of Greenwich Mean Time.


Solstice and Equinoxes


It is a day of the year when the duration of day and night is equal and the position of the sun is in its zenith. In year equinoxes occurs twice.



Like equinoxes solstice also occur twice a year. This is the time when the sun riches either its highest are lowest point at noon. It leads to the result of longest and shortest day of the year.

  • June solstice (approximately June 20-21). This day begins summer in the Northern hemisphere and winter in the Southern hemisphere. This day is the Longest in the year. In the Northern Hemisphere and shortest. In the Southern hemisphere. On this day, the Sun is directly overhead the tropic of Cancer (23.5 degree at moon).
  • September Equinox (approximately September 22-23): This dry begins fall in the Northern hemisphere and spring in the Southern hemisphere. There are 12 hours of dry light and 12 hours of darkness at all points on the Earth's surface on the two equinoxes. Sunrise is at  60 m. and sunset is at 6 pm.
  • December Solstice (Approximately December 21-22): This dry begins summer in the Southern hemisphere and is the longest dry in the Southern hemisphere. It begins winter day in Northern hemisphere and is the shortest day of the year in the Northern hemisphere. The Sun is directly overhead the Tropic of Capricorn on the December.
  • March Equinox (Approximately March 21-21): Spring solstice equinox this day begins tell in the Southern hemisphere and spring in the Northern hemisphere. There are 12 hours of day light and 12 hours of darkness at all the points on the Earth's surface on the two equinoxes. Sunrise is at 6 a.m. and Sunset is at 6 pm. local (so far) time zone most points on the Earth's surface.




When the light of the Sun or the Moon is blocked by another body, the sun or Moon is said to be in eclipse. The Sun, Earth and Moon are in a straight line Eclipses of the Sun is a solar eclipse and the Moon is a inner eclipse.


Solar Eclipse


It is caused when the moon Revolving around the Earth comes in between the Earth and the Sun, thus making a part or whole of the sun invisible from a particular part of the Earth thus, the Day.

Type of Solar Eclipses

  • Total Eclipse: Occurs when the Sun is completely obscured from rich. Instead, the Sun intense light is replaced by dark silhouette of the Moon that is outlined by the Sun's corona (the super-heated plasma extending out from the Sun.
  • Annular Eclipse: Occurs when the Sun and Moon are exactly in line but Moon appears smaller than the Sun. During on annular eclipse, the Sun appears as a bright
  • Partial Eclipse: Occurs when the Sun and Moon are not completely aligned and the Sun is partially obscured.
  • Hybrid Eclipse: is a combination of total and annular eclipse that takes place when a total eclipse changes to an annular eclipse or vice-versa along different sections of the eclipse's path.

Lunar Eclipse

  • When the Earth comes between the Moon and the Sun, the shadow cast by tlie Earth on the Moon results in a lunar eclipse. It is occur at night.




Earth Theory

  • A large number of hypothesis were put forth by different philosophers and scientists regarding the origin of the earth. One of the earlier and popular arguments was by
  • German philosopher Immanuel Kant. Mathematician
  • Laplace revised it in 1796. It is known as Nebular
  • The hypothesis considered that the planets were formed out of a cloud of material associated with a youthful sun, which was slowly rotating. Later in 1980, Chamberlin and Moulton considered that a wandering star approached the sun. As a result, a cigar-shaped extension of material was separated from the solar surface, As the passing star moved away, the material separated from the solar surface continued to revolve around the sun and it slowly condensed into planets. Sir James Jeans and later Sir Harold Jeffrey supported this argument. At a later date, the arguments considered of a companion to the sun to have been consisting. These arguments are called binary hypothesis. In 1950, Otto Schmidt in Russia and Carl Weizasear in Germany somewhat revised the ‘nebular’ hypothesis.
  • Modern Theories: The most popular argument regarding the origin of the universe is the Big Bang theory. It is also called expanding universe hypothesis. Edwin Hubble, in 1920, provided evidence that the universe is expanding. As time passes, galaxies move further and further apart.


Continental Drift theory


  • It was proposed by Wegener in 1912.
  • According to the theory billion years ago all continents were joined together into one big landmass called as Pangaea. On the other hand all ocean joined together were called as Panthalassa.
  • Pangaea floated over Panthalassa.
  • Pangaea broke into two parts due to gravitational force and buoyancy.
  • The northern part was known as Laurasia and southern part was known as Gondwanaland. These landmass were further splitted into smaller landmass forming different continents.
  • Tethys sea was formed when Pangaea first splitted into Laurasia and Gondwanaland.
  • Jig-saw fit conventional current theory and plate tectonic theory supports it.


Plate Tectonic theory


  • It was argued that the outermost part of the earth's interior consists of two layers: the lithosphere consists of crust, and the solidified uppermost part of the mantle. Below the lithosphere lies the asthenosphere, which is the inner part of the upper mantle. Asthenosphere is in semi fluid state. Lithosphere floats on the asthenosphere and is broken up into lithospheric plates.
  • Plate Tectonics theory defined atectonicplateor lithospheric plate as a massive, irregularly shaped slab of solid rock, composed of both continental and oceanic lithosphere. The plates move horizontally over the asthenosphere as rigid units. Lithosphere is divided into seven major and some minor plates. The 7 major plates are: (i) Antarctica plate, (ii) North American plate, (iii) South American plate, (iv) Pacific plate, (v) India-Australia-New Zealand plate, (vi) Africa plate and (vii) Eurasian plate. Also there are minor plates like (i) Cocos plate, (ii) Nazca plate, (iii) Arabian plate, (iv) Philippine plate, (v) Caroline plate and (vi) Fuji plate.
  • Three types of plate boundaries are found :
  1. Transform boundaries occur where the plates slide or grind with each other (San Andreas fault).
  2. Divergent boundaries occur were two plates slides apart from each other (Mid-Atlantic Ridge).
  3. Convergent boundaries occur where two plates slide towards each other. Found near pacific boundary North and South America.


Geological Time Scale





Age/years Before Present

Life/Major Events


Cainozoic (From 65 million years to the present times)


Holocene Pleistocene

0 -10,000

10,000 - 2 million

Modern Man

Homo Sapiens








2 - 5 million

5 - 24 million


24-37 Million

37 - 58 Million

57 - 65 Million

Early Human Ancestor Ape : Flowering Plants and Treees Anthropoid Ape

Rabbits and Hare

Small Mannals :

Rats - Mice


Mesozoic 65-245 Million Mammals





65 - 144 Million

144-208 Million

208-245 Million

Extinction of Dinosaurs

Age of Dinosaurs

Frogs and turtles 


Palaeozolc 245-570Million











245-286 Million


286-360 Million


360-408 Million

408-438 Miillion


438-505 Million

505-570 Million 

Reptile dominate-replace Amphibians

First Reptiles:

Vertebrates: coal beds


First trace of life on land: plants first Fish

No terrestrial Life: 

Marine Invertebrate

Proterozolc Archean Hadean  



Pre-Cambrian  570 million 4,800 million






570-2,500 millon

2,500-3,800 million 

3,800-4,800 Million

Soft-bodied arthropods

Blue green Algae;


Oceans and Continents

from-Ocem and

atmosphere are rich in carbon dioxide

Origin of Stars Supernova Big Bang

5,000-13,700 Million



5,000 Miilion


12,000 Million

13,700 Million  

Origin of the sun


Origin of the universe


Composition of the earth

Earth’s Interior

  • Interior of the earth is composed of non-uniform material. Velocity of seismic waves proves that the earth's interior consists of three different layers; crust (ii) mantle and (iii) core. These layers are distinguished on the basis of their (i) physical and chemical properties, (ii) thickness, (iii) density, (iv) temperature, (v) metallic content and (vi) rocks.


The Outermost layer of the earth is called crust. Thickness of earths crust varies from 1 to 80 km. It is divided into upper and lower crust. On average continental crust is 50 km

  • Upper crust has the density of 2.69-2.74
  • Lower crust has the density of 3-3.25
  • The upper crust has lower density due to the presence of lower density minerals than in lower crust.
  • It composed of variety of igneous, metamorphic and sedimentary rocks.
  • Most common rock found in earth's crust are igneous rocks. It covers 90% of the earth crust's volume.
  • The temperature of crust increases with depth. Near mantle its temperature is recorded between 200°C to 400°C.
  • It consists of different minerals like oxygen (46.6%), silicon (27.7%), aluminium (8.1%), iron (5%), others (12.6 %).
    • The continent crust is thicker than the oceanic crust.
  • The boundary between crust and mantle shows sudden increase in density and velocity of sesmic wave wich is called as moho-discontinuity.



  • The second of the interior of the earth.
    • It extends form 60 km to 2900 km. depth.
  • Divided into two layers : upper mantle (60 - 1000 km) and lower mantle (1000 - 2900 km)
    • Silica and magnesium are the dominant minerals found alongwith iron.
  • The upper part of the mantle is in solid state as compared to its lower part.
  • There is sudden change in the composition and structure of the interior of the earth at mantle core boundary. This zone of change in average density (5.5 to 10) is called as Wichert-Guttenberg discontinuity.


  • Core is the inner most layer of the earth's interior.
  • Its density at the boundary of mantle is 10.3 and increases with increase in depth.
    • It contains 32 percent of the total mass of the earth.
    • It occupies 16 percent of the total volume of the earth.
    • It is divided into two sub-zones. Outer core and inner core.
  • The line dividing core into inner and outer core is at 5150 km of depth from earth's crust.
  • The outer case is mainly a liquid layer of nickel and iron. The inner care is in solid state mainly consiting of iron nickel alloy.





Movement in earth causes vast changes. The forces affecting earth, crust is divided into two on the basis of their origin:

  1. Endogenetic forces
  2. Exogenetic forces
    • Endogenetic forces result in sudden movement or diastrophic movement.
  • Sudden movement results in volcanic eruption and earthquake.
    • Diastrophic movement results in tensional and compressional forces.
    • Cracks and faulting is the result of tensional force.
    • Warping and folding is associated to compressional force.
  • Rift valley is formed due to tensional and compressional force.
    • Wave like bends in crustal rocks due to tangential compression force resulting in horizontal movement is called as fold.
    • There are five major types of folds: symmetrical, asymmetrical, monoclinal, isoclinal and recumbent folds.
    • Fracture in the crustal rock causing displacement of rock is called as fault.
    • There are four types of faults: Normal faults, Reverse faults, Lateral or strike-ship faults and Step faults.
    • Exogenetic forces are generated form the atmosphere due to varying combination of temperature and moisture.
    • Exogenetic forces result in denudational processes (denudation = weathering + erosion)





Movement of the heated material from the interior of the earth to a towards the surface is called as volcanism. Volcano is a vent opening through which these heated material like gases, water, liquid lava and fragment of rocks are ejected causing widespread of devastation.


Distribution of Volcanic activity in world

(1) Circum-Pacific belt

(2) Mid-continental belt

(3) Mid-Atlantic belt

(4) Intra-plate volcanoes


(1)        Circum-Pacific belt: The 'Ring of Fire', the belt starts from Erebus Mountain of Antarctica, running through Andes and Rockies mountains reaches Alaska from where it enters Asiatic coast turning eastward spreading over volcanoes of Island arc (Sakhaline, Kamchatka, Japan, Hawaii and Aloutin etc.) It is the subduction zone.


(2)         Mid-Continental belt: Convergent zone of continental plates. This belt includes the volcanoes of the Alpine mountain chain alongwith Mediterranean sea and reaches the fault zone of Africa in the east. It is formed due to collision of Eurasian plates with African and Indian plates.


(3)        Mid-Atlantic belts: It is a zone of divergent where two niates solit and form new landmass. Here volcanoes of Atlantic stretching 11,300 km. The HeKia volcanic mountain of Iceland makes Iceland world's largest volcanic Island.


(4)        Intra-Plate volcanoes: The massive eruption that occurs in north-western part of North America, Indian Peninsula, Parana, of Barazil and Paraguay sometimes in past are part of intra-plate volcanoes.


Types of Volcanoes

(1)        Active Volcanoes   : The volcanoes which have at least erupted once in past 10,000 years. Mt. Etna (Sicily), Hekia (Iceland), Erta Ale (Ethiopia) Bromo (Java), Nevado del Ruiz (Colombia) etc. are in active state.


(2)        Dormant Volcanoes: They are active volcanoes but are not erupting at present Mt. Fuji (Japan) and Mt. St. Helen (Washington) are such examples.


(3)        Extinct Volcanoes: They are those volcanoes which have not erupted at least for 10,000 years and are not expected to erupt in future. Mt. Kilimanjaro (Tanzania) and Mt. Buninyong Australia are examples of extinct volcanoes.


Classification based on periodicity of eruptions


(a)   Active volcano: Such volcanoes erupt frequently or at least have erupted in recent periods like barren islands in India and Mt Stromboli in Italy (Lighthouse of mediterranean sea).

(b)  Dormant volcano: They are known to have erupted and show signs of possible eruption in future like Mt Kilimanjaro.


(C) Extinct volcano: They have stopped erupting but retain the features of volcanoes.




·                     An earthquake is basically the vibration of earth produced by the rapid release of energy. This energy radiates in all directions from the source, in the form of waves. It is accompanied by a rumbling sound and tremors. The place of origin of an earthquake is its focus. The point on the earth's surface vertically above the focus is the epicenter. Intensity of vibrations is the maximum near the epicenter.

·                     Seismic sensors, located throughout the world can record the event.

·                     The magnitude of energy released by an earthquake is measured by the Richter scale. It ranges between 0 and 9.

·                     Elastic Rebound theory explains the mode and cause of earthquake.


Causes of Earthquake

·                     Most of the earthquakes are related with compressional or tenssional stresses built up at margins of the moving lithospheric plates.

·                     Plates are dynamic and often push into one another or are pulled apart at times they even slide over each other. When the stress is too much these rocks break and the beings shake causing earthquake. The process of volcanicity, along with anthropogenic and plate tectonic result in earthquake. Sometimes, the tremendous energy released by atomic explosions or by volcanic eruptions can also produce earthquakes, but these events are usually too weak and infrequent.


Earthquake Waves

Earthquakes generate pulses of energy which are called seismic waves that can pass through the entire Earth. There are three major types seismic waves.

·                     Primary (P) waves, of short wavelength and high frequency, are longitudinal waves which travel not only through the solid crust and mantle but also through the liquid part of the earth's core. This is compression wave. Its speed is highest so it reaches first at earth surface.

·                     Secondary (S) waves, of short wavelength and high frequency, are transverse waves which travel through all the solid parts of the Earth but not the liquid part of the core. It is also called distortional wave and shear wave.

·                     Long (L) Waves, of long wavelength and low frequency, are confined to the skin of the earth's crust, thereby, causing most of the earthquakes structural damage. Long (L) Wave is also called long period wave. These waves cover the longest distance of all seismic waves.


Distribution of Earthquakes belts in World


I.             Circum Pacific Belt accounts for 66% of total earthquakes. Circum Pacific belt runs through the west coasts of North and South America, Aleutian Islands and the island group along the eastern coast of Asia.


II.            Mid-Atlantic Belt causes 11% of total earthquakes. This range causes mid-atlantic Ridge, and several islands nearer the ridge. Earthquake even here are of moderate to shallow magnitude


III.       Mid Continental Belt causes 21% of total earthquakes. Mid-continental mountain belt runs through the middle of Asia from east to west and goes beyond the Mediterranean Sea. Its axis lies along the mountain belt of the Himalayas, Caucasus, and the Alps.

·                     The Himalayas, making the great mountain wall of the north, also happen to form the northern margin of the Indian plate and hence are marked by frequent and severe earthquakes.


IV.        Others

·                     Seismicity may also occur away from such regions. Such seismic activities, located within the plates away from the plate margins, are called in-plate seismicity.

·                     They are generally confined to the weaker zones of the earth?s crust.

·                     These weaker zones are represented by faults or fractures within the earth?s crust and are generally less intense than die ones found near the plate margins.

·                     One such zone of in-plate seismicity is the Narmada-Son lineament, cutting across the northern plane.

·                     The earthquake of January 26, 2001 of Gujarat was also caused by the growing 'in-plate stress?: whole Kutch is a fault. Bhuj, lies close to the Allah bund fault.

·                     Hence, in-plate seismicity is due to the reactivation of concealed shields (stable parts of the Earth) and release of energy.



The Earthquake Zones in India


On the basis of intensity of the earthquakes a map of India has been published by the Meteorological Department in collaboration of the Indian Standard Institution. The map shows the five seismic zones based on modified Mercalli scale.

Zone I - Intensity V or below (feeble, slight, moderate rather strong)

Zone II - Intensity VI (strong)

Zone III - Intensity VII (very strong)

Zone IV - Intensity VIII (Destructive Zone)

Zone V - Intensity more than VIII (Disastrous, Catastrophic)

Zone I - No area of India is currently classed, in zone I

Zone II - Includes Southern Punjab and Haryana, certain parts of Plains of Uttar Pradesh, Eastern Rajasthan, Coastal areas of Odisha and Tamilnadu. This is the low damage rests zone.

Zone III: Covers Southern and South Eastern parts of Rajasthan, larger parts of Madhya Pradesh, Maharashtra, Karnataka, Jharkhand and Northern and North-Western parts of Orissa.

Zone IV: Covers Jammu and Kashmir, Himachal Pradesh, Northern parts of Punjab, Haryana, Delhi, Eastern Uttar Pradesh, Tasai and Bhabhat regions, the Himalayan areas of Uttaranchal, Bihar and Sikkim

Zone V: Covers certain parts of Jammu and Kashmir, Himachal Pradesh, Uttranchal, Monghy, and Darbhanga districts of Bihar, Northern part of India and Kutchh region of Gujarat.

Some specific areas where the waves are not reported, such zone is called the 'shadow zone'.





Earth is composed of various elements. These are in a solid state in the outer layer of the earth and in molten state in the interior. About 98% of the total crust of the earth is composed of eight elements like oxygen, silicon, aluminum, iron, calcium, sodium, potassium and magnesium. Out of these, silicates carbonates and oxides make up a large group of them. Elements in the substances. These substances are known as minerals. Quartz, for example, has two elements, silicon and oxygen, united together form a compound known as carbonate of lime. The basic source of all minerals is the hot magma in the interior of the earth. When magma cools down, crystals of minerals appear and a systematic series of minerals are formed in sequence so as to from rocks. The earth is composed of rocks. A rock is an aggregate of one or more minerals. There are three types of rocks on the basis of their formation. (1) Igneous, (2) Sedimentary and (3) Metamorphic rocks.





The earth is composed of rocks. A rock is an aggregate of one or more minerals. There are three types of rocks on the basis of their formation.

(1) Igneous,

(2) Sedimentary and

(3) Metamorphic rocks.


Igneous Rocks


·                     Igneous Rock is derived from latin word 'ignis' meaning fire.

·                     It is formed when magma cools and solidifies either on the surface of the earth or inside the earth.

·                     Igneous rocks have been forming since the earth was born.

·                     Out of three kinds of rock - igneous, sedimentary and metamorphic- they were first to be formed and hence they are called Primary Rocks and even parent rock.

·                     It is characterised by hardness which leads to no percolation of water resulting in no chemical weathering. But the grains of igneous rocks are affected by mechanical on physical weathering.

·                     No fossil is formed and is associated with volcanic activities.

·                     Igneous rocks are classified into (1) extrusive - it is formed when lava gets solidified on reaching the surface of the earth and (2) intrusive - it is formed by solidification of magma at moderate depths beneath the earth's surface and its rate of cooling is slow.

·                     Intrusive rocks are of two types such as plutonic rocks and hypabyssal rocks.

·                     Plutonic rocks are magmas which cooled deep inside the earth with a slow speed as temperature over there is high. These rocks are of coarse grained like granite.

·                     Hypabyssal rocks are volcanic magma which cools and solidifies in cracks, pores and hollows beneath the earth's surface, pores, batholiths, lopoliths, phacoliths, laccoliths, sills and dykes are its examples.


Sedimentary Rocks


The word ?sedimentary? is derived from the Latin word sedimentum, meaning settling. These are formed by the sediments brought by rivers, wind and glaciers. Rocks of the earth's surface are exposed to denudational agents, and arebroken into smaller fragments. Such fragments are transported by different exogenous agencies and deposited. These deposits due to pressure and compression turn into rocks. Sedimentary rocks are sandstone, shale and conglomerates. These are also formed from organic matter derived from plants or animal remains and thus are called as fossil rocks. Coal and limestone are such sedimentary rocks. Sedimentary rocks are classified into three major groups:

(i)         Mechanically formed - Sandstone, Conglomerate, limestone, shale, loess.

(ii)        Organically formed - e.g. geyserite, chalk, limestone, coal etc.

(iii)       Chemically formed - like chalk, limestone, halite, potash etc.


Metamorphic Rocks


·                     Metamorphic means 'change of form'. Metamorphism covers all the processes by which rocks are altered in their mineralogy, texture and internal structure owing to external sources of heat, pressure and introduction of new chemical substances. Due to metamorphism, igneous and sedimentary rocks get totally changed in their physical state, chemical composition and crystallization of minerals. Granite is converted into gneiss, clay and shale are transformed into slate, and coal is transformed intc graphite, limestone changes into marble. Gneiss, slate, schist and marble are examples of metamorphic rocks.


Four types of metamorphic rocks are recognized on the basis; of its composition:

(1)   Contact or thermal metamorphism (due to heat)

(2)   Dynamic and regional metamorphism (due to pressure)

(3)  Hydro-metamorphism (due to hydro-static pressure)

(4)  Hydro-thermal metamorphism (due to water and heat)





·                     Oceans and continents are first order of relief.

·                     Mountains, plains and plateau are second order of relief.

·                     When the agents of erosion acts on these second order of relief the third order of relief is formed Example: land forms formed by agents like river, wind and glacier etc.







·                     Mountains are significant relief features of the second order on the earth's surface. A mountain may have several forms.

·                     Mountain Ridge - a system of long, narrow and high hills.

·                     Mountain Range - a system of mountain and hills with several ridges.

·                     Mountain Chain - Which have several parallel, long and narrow mountains belonging to different periods.

·                     Mountain Group - Consists of several unsystematic patterns of different mountain system.

·                     Mountain System - Consists of different mountain ranges belonging to the same period.


·                     Classification based on mode of origin


1.         Structural or Tectonic Mountain: These mountains come into existence due to tectonic forces. They are of three types.

(a)        Fold Mountains: These are created by compressive forces. Fold mountains are of three types:

(i) Young Fold mountain: Some young fold

mountain are Alps in Europe, the Rockies of North America, the Andes of South America, the Himalayas of Asia and Atlas of North Africa. These young fold mountains are still rising under the influence of the earth's tectonic forces.

(ii) Matured Fold mountain: The Urals, the

Appalachians, the Tien Shan and the Nan

Shan were formed during an earlier mountain-building period.

(iii) Old Fold mountain: Folded mountains which have originated before tertiary period are called old fold mountain e.g. - Caledonian and

Hercynian, Vindhyachal, Aravalis. These are also called relict fold mountain because of denudation.

(b)        Block Mountains: Originated by tensile forces

leading to the formation of rift valleys e.g. Wasatch range in Utah (USA), Vosges and Black forest mountain (Europe), Salt Range (Pakistan) and Sierra Nevada mountain (USA). They are known as fault block mountains.

(c)        Dome Mountains: Originated by magnatic intrusions and upwraping of the crustal surface e.g. Normal domes. Lava domes, Laccolithic domes, Salt domes etc.

2.         Mountain of accumulation or volcanic mountain: Formed due to accumulation of volcanic material. Mount   Mauna Loa in Hawai islands, Mt. Fuji Yoma of Japan and Mt. Popa in Central Myanmar are some of examples.

3.         Erosional or Relict Mountain: These are formed due to the erosion of the earlier mountains. Its examples are the Vindhyanchal range, Aravalis, Satpura, Eastern Ghats, and Western Ghats in India.




  • Plateaus are extensive area characterized by flat and rough top surface, steep sidewalls which rise above the neigh bouring ground surface at least for 300 metres.
  • Covers about 18% of the total earth's land  surface.


Classification of plateau

  1. Plateau formed by exogenetic processes

(i) Glacial Plateau, e.g. Garhwal plateau, Greenland, Antarctica.

(ii) Fluvial Plateau e.g. Kaimur plateau, Bhander plateau, Rewa Plateau, Rohtas Plateau.

(iii) Aeolian Plateau e.g. Potwar Plateau (Pak), Loess plateau (China)

  1. Plateau formed by endogenetic processes

(i) Intermontane Plateau: The plateaus which are partly or fully enclosed by mountains are known as intennontane plateaus. These are the results of the mountain-building process which was accompanied by a vertical uplift of the adjoining enclosed lands. e.g. Tibetan plateau, Bolivian plateau, Peruvien plateau, Columbian plateau and Mexican plateau.

(ii) Piedmont Plateau: Situated at the foot of a mountain, they are bounded on the opposite side formerly high have now been reduced in elevation by various agents of erosion, e.g. Appalachian plateau, Patagonien plateau (Argentina).

(iii) Dome Plateau:  Formed when land mass is uplifted e.g. Ozark Plateau (USA), Chotanagapur plateau (Jharkhand)

(iv) Lava Plateau:  Formed due to accumulation of thick layers of basaltic lava e.g. Columbia plateau (USA), Mahabaleshwar plateau, Panchgani tableland.

(v) Continental Plateau: They rise abruptly from the lowlands or from the sea. e.g. Deccan plateau of India, Ranchi plateau, Shillong plateau, Columbia plateau (USA), Mexican plateau etc.

(vi) Coastal Plateau : e.g. Coromandel coastal upland of India.

(vii) Desert Plateau: Arabian Plateau.

(viii)Humid Plateau: e.g. Shillong Plateau, Assam Plateau, Mahabaleshwar Plateau etc.

(ix) Young Plateau: e.g. Idaho Plateau (USA), Colorado Plateau (USA), Mahabaleshwar Plateau, Khandala Upland (Maharashtra).

(x) Mature Plateau: e.g. Ranchi Plateau, Hazaribagh Plateau (Jharkhand), Appalachian Plateau (USA).

(xi) Rejuvenated Plateau: e.g. Missouri Plateau (USA).




  • A plain is a relatively flat and low-lying land surface with least difference between its highest and lowest points. They are formed by endogenetic forces, erosion and exogenetic deposition.

Plains have been divided into:

(1)  Structural Plains

(2)  Erosional Plains

(3)  Depositional Plains


Structural Plains

  • These plains are uplift of a part of the sea floor usually bordering a continent, that is, the continental shelf.
  • Depressed areas which make up very extensive lowlands on the earth.
  • The underlying horizontal beds of rocks are relatively undisturbed by the earth's crustal movements.
  • Such plains include the great plains of Russian platform, the great plains of USA and the Central lowlands of Australia.
  • The coastal plain lying between the Appalachian Piedmont Plateau and the Atlantic coast of south-eastern United States is an example of an uplifted coastal plain.



Erosional Plains

  • These are formed when an elevated tract of land, for instance, a mountain, a hill or a plateau is worn down to a plain by the process of erosion.
  • The surface almost smooth is termed as a peneplain river, ice and wind eroded regions.
  • Northern Canada, northern Europe and west Siberia are examples of such ice-eroded plains.
  • Parts of Sahara in Africa are wind-eroded plain surface.
  • The rivers by widening their banks and lowering the higher land between them have eroded parts of the Amazon basin into streameroded type of plains.


Depositional Plains

  • The plain formed by deposition of sediments occurs due to the actions of rivers, glaciers, wind, sea wave etc. Different types of depositional plains are:
  1. River Plain: These are formed by the alluvium brought down by the rivers. The Indo-Gangetic plain in Indian subcontinent, Hwang-ho plain of north China and Povalley in North Italy are some examples of alluvial plain. (1) Food plain (2) Deltaic plain (3) Pediment plain
  2. Lacustrine plain: A plain that originally formed in a lacustrine environment. It is a lake basin Valley. Kashmir is its example.
  3. Lava Plain: It is formed due to volcanic eruption.
  4. Loess Plain: Formed due to wind deposition. Plains of N. China and Russian Turkistan is formed due to it.
  5. Marine Plain: Develops near coast of shallow sea coastal areas of Netherlands Germany, Denmark and the Gulf of Mexico in U.S.A.
  6. Galacial Plain: Formed due to deposition of galacial and debris.

(a) Till plain (b) Morainic plain (c) Out wash plain



Fluvial Landforms



  • Running water is the most important agent of denudation. Flow of a river or a stream is very strong. River action includes weathering and mass wasting causes fluvial denudation.

Erosion by rivers it is performed in two ways mechanical erosion and chemical erosion they are fertile and economic, importance is dependent on the type of sediments brought by agents of denudation.

  1. Solution/Corrosion: It is a type of chemical weathering in which most of the salts are removed from the bedrocks through the process of carbonation.
  2. Abrasion/Corrosion: Involve the removal of loosened material of the rock of valley walls and floor by actions of erosional tools.
  3. Attrition: Wear and tear of transported material when they roll and collide with each other.
  4. Hydraulic Action: It involves breakdown of  rocks of valley sides due to the impact of water currents. It is both mechanical and chemical process.

River Land Forms

  1. Upper Course landforms: V-shaped valley, gorges, canyons, rapids and water fall these are mostly erosional plain of river. The river is at youth stage when it is at upper course.
  2. Middle Course landforms: Alluvial far and cone, meanders and oxbow lake are formed in the middle course of a river. The river achieves maturity stage in this course. Depositional features are formed in this course.

III. Lower Course landforms: Delta is formed at the lower course of the river. It is also known as old stage for a river.




  • Depositional feature of triangular shape at the mouth of a river debouching either into a lake or a sea is called a delta.

Types of Delta

(a) Bird's foot delta, Ex-Mississippi delta

(b) Arcuate delta, Ex-Nile, Ganga, Mekong.

(c) Estuarine delta : Amazon, Ob, Vistula, and Tapi.

Their fertility and economic importance is dependent on the type of sediments brought by agents of denudation.


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