(IGP) GS Paper 1 – India & World Geography – “Lithosphere”

Integrated Guidance Programme of General Studies for IAS

Subject – India & World Geography
Chapter : Lithosphere

Our Planet Earth:

  • Earth, the home to mankind, is a unique member of the solar family.
  • The fifth biggest planet in the solar system, its uniqueness lies in its
    habitability vertically overhead at the equator on two days each year, i.e.
    on March 21st and September 23rd. These days are called equinoxes meaning
    ‘equal nights’ because on these two days all places on Earth have equal days
    and nights.
  • After the March equinox, the sun appears to move northwards and is
    vertically overhead at the Tropic of Cancer on June 21st. Thus is known as
    the summer solstice, when the northern hemisphere will have its longest day
    and shortest night.
  • By December 22nd, the sun is overhead at the Tropic of Capricorn. This
    is the winter solstice when the southern hemisphere will have its longest
    day and shortest night.

Movement of Earth:

  • The earth moves in space in two distinct ways. It rotates on its own
    axis from west to east once in every 24 hours causing day and night.
  • It also revolves round the sun in an orbit once in every 365 ¼ days
    causing the seasons and the year.
  • The earth revolves round the sun in an elliptical orbit at a speed of
    18.5 miles per second.
  • A normal year is taken to be 365 days, and an extra day is added every
    four years as a Leap Year because 1/4th day of every year becomes 1 day.

Latitudes and Longitudes:

  • Latitude is the angular distance of a point on the Earth’s surface,
    measured in degrees from the centre of the Earth.
  • Longitude is the angular distance, measured in degrees along the
    equator, east or west of the Prime Meridian (the meridian that passes
    through Greenwich near London).

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Standard Time and Time Zones:

  • Most countries adopt their standard time from the central meridian of
    their countries.
  • The whole world has been divided into 24 Standard Time Zones.
  • Each zone, therefore, is separated by 15º longitudes or by one hour.
  • Larger countries like USA, Canada and Russia having greater east-west
    stretch have to adopt several time zones.

International Date Line:

  • The International Date Line in the mid-Pacific curves from the normal
    180º meridian at the Bering Strait, Fiji, Tonga and other island to prevent
    confusion of day and date in some of the island groups that are cut through
    by the meridian.

Earth’s position with respect to Moon:

  • Apogee: The period of the farthest distance between the moon and the
    earth (407,000km) is called apogee.
  • Perigee: The period of the nearest distance between the moon and the
    earth (356,000 km) is called perigee.

Earth’s position with respect to Sun:

  • Perihelion: The period of the nearest distance between the earth
    and the sun (147 million kilometer) is perihelion. It happens on January 3.
  • Aphelion: The period of the farthest distance between the earth
    and the sun (152 million kilometers) is called aphelion.  It happens on July

Earth’s Interior:

  • Temperature inside the Earth increases with depth.
  • Experiments have confirmed that the temperature increases at the rate of
    1ºC for every 32 metres.
  • The Core and the Mantle are separated by the Guttenberg discontinuity,
    while the Mohorovicic discontinuity separates the Mantle from the Crust.
  • Besides, the upper granitic and the lower basaltic layers of the crust
    are separated by a seismically determinable boundary called the Conrad

Plate Tectonics:

  • The theory of Plate Tectonics states that the lithosphere consists of
    several individual segments called plates.
  • About twenty such plates have been identified.
  • Of these, the largest is the Pacific plate while the Juan de Fuca plate,
    of the western coast of North America, is the smallest.

Continental Drift Theory:

  • F B Taylor postulated his concept of ‘horizontal displacement of the
    continents’ in the year of 1908 to explain the problems of the origin of the
    folded mountains of tertiary period.
  • Alfred Wagener propounded his concept on continental drift in the year
    1912 which is also known as displacement hypothesis. It was propounded to
    explain the global climatic changes.

Sea Floor spreading:

  • The concept of sea floor spreading was first propounded by professor
    Hary Hess in the year 1960.
  • Collisions can occur between two oceanic plates, one oceanic and one
    continental plate or two continental plates.
  • A deep-ocean trench is formed adjacent to the zone of subduction while
    the upwelling magma generated by a complex process of melting of the
    subducting crust cause explosive volcanic eruptions.


  • An earthquake is basically the vibration of Earth produced by the rapid
    release of energy.
  • This energy radiates in all directions from the source, focus, in the
    form of waves.
  • The waves are very much analogous to those produced when a stone is
    dropped into a calm pond.
  • Seismic sensors, called seismographs located throughout the world can
    record the event.

Earthquake Waves:

  • Earthquakes generate pulses of energy called seismic waves that can pass
    through the entire Earth. Three major divisions of seismic waves have been
  • 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.
  • 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.
  • 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.

Seismic Zones of India:

  • Based on the intensities of earthquakes recorded on the Modified
    Mercalli scale, India is divided into five seismic zones.
    Zone 1             Intensity V or below
    Zone 2             Intensity VI
    Zone 3             Intensity VII
    Zone 4             Intensity VIII
    Zone 5             Intensity IX and above
    ‘Zone 5’ covers areas with a probable magnitude of 8 or more on the Richter
  • Zone I is the least seismic prone zone with magnitude of up to 4.9 on
    the Richter scale.
  • Delhi falls in ‘Zone 4’ and is prone to earthquakes of magnitude between
    7 and 7.9 on the Richter scale.
  • The Rann of Kutch, the entire Northeast, the Andamans, certain parts of
    Jammu and a good part of Uttaranchal come under ‘Zone 5’.

Classification of Rocks:

On the basis of the mode of formation, rocks are usually classified into
three major types:

1. Igneous Rocks

  • Igneous rocks are parents of all other rocks and are also known as
    primary rocks.
  • They have been forming since earth began and are still formed in regions
    of volcanic activity.
  • Extrusive igneous rock is the name given to magma eruption and
    solidifying after escape of gases as lava on reaching the surface of earth.
  • Basalt is a typical example of extrusive type, covering 500,000 sq km of
    Peninsular India in its north-western part.
  • The intrusive igneous rock is formed by solidification of magma at
    moderate depths beneath the earth’s surface.
  • The granite and the dolerite are the most common examples of such rocks.

2. Sedimentary Rock

  • Although three-fourths of the earth’s surface is covered with
    sedimentary rocks, they make up only about 5 per cent of the volume of the
    earth’s crust.
  • As sedimentation is favoured by water, most of the sedimentary rocks
    have been formed under water.
  • The loess is one example of fine sand carried by wind and deposited as
    wind-borne sedimentary rock as in north-western China and Indian
  • The conglomerate is a collection of round pebbles taken from a sea shore
    or a riverbed mixed and bound together by some cementing stuff.
  • Two well-known examples of sedimentary rocks of organic origin are coal
    and the limestone.

3. Metamorphic Rocks

  • In Greek language, the word ‘metamorphic’ means ‘change of form’.
  • These rocks are formed under conditions similar to those producing
    igneous rocks.
  • The process of metamorphism takes place at depths under the pressure of
    overlying rocks or as a result of contact with a hot igneous material.

Important Metamorphic rocks

Basic rocks                  Metamorphosed
Limestones                  Marbles
Sandstones                  Quartzites
Shales/Clays                Slates/Schist
Granites                       Gneisses
Gabbro                        Serpentine
Amphibolites               Basic granulites
Basaltic rocks               Eclogite

Classification of Landforms:

  • There are three major landforms- mountains, plateaus and plains.


  • An uplifted portion of the earth’s surface is called a hill or a
  • In our country, a mountain is differentiated from a hill, when its
    summit or top rises to more than 900 metres above the base.
  • Those with less than this elevation are called hills.
  • On the basis of their origin or mode of formation, the mountains are
    classified as structural or tectonic, residual or dissected and volcanic.


  • A plateau is an elevated area generally in contrast to the nearby areas.
  • It has a large area on its top unlike a mountain and has an extensively
    even or undulating surface.
  • The rocks of the plateau are layered with sandstones, shale’s and
  • The great Deccan Plateau with its slope towards east is a tilted plateau
    in our country.
  • The plateaus are of three types on the basis of their situation (i)
    intermontane, (ii) continental, (iii) piedmont plateaus and (iv) Lava


  • A relatively flat and a low-lying land surface with least difference
    between its highest and lowest points is called a plain.
  • A plain may be as low as 30 metres to the east of Mississippi river near
    the Appalachian range and as high as 1,500 metres above sea level to the
    west of the river.
  • Plains can be placed according to their position and surface relief but
    are better classified on the basis of their mode of formation.
  • They are sub-divided into structural, erosional and depositional plains.

Drainage Patterns:

  • The riverine topography develops in fully evolved drainage basin.
  • A main stream or a river with all its tributaries produces a river
    system or a drainage basin.
  • The higher ground separating the two drainage basins is called the
    watershed or a water divide.
  • The uplands or the mountains through which a river flows describe its
    catchment area from over which it draws its water.
  • Originally when rivers flow in the direction of the slope or as a
    consequence of the slope, they are called the consequent streams.
  • As soon as such a river is joined by its tributary, it is called the
    subsequent stream.


  • The depositional feature of almost triangular shape at the mouth of a
    river debouching either in lake or a sea is called delta.
  • The word ‘delta’ derived from Greek letter, was first used by Greek
    historian Herodotous for the triangular depositional feature at the mouth of
    the Nile river.
  • An average delta consists of three beds of sediments e.g. (i) topset
    beds, (ii) foreset beds and (iii) bottom set beds.

Ground Water:

  • There are about 1360 million km3 of water in the world of which 1322
    million km3 are in the oceans.
  • Of the remaining 4 million km3, 76.8 per cent is locked up in ice caps
    and glaciers, 22.6 percent is in ground water (water below the surface),
    0.56 per cent is in surface water (streams, rivers and lakes), and only 0.04
    per cent is in the atmosphere in the form of water vapour.


  • Fresh water from land enters the ocean through rivers, streams and
    ground water.
  • The embayment’s where fresh water from the land meets salt water from
    the ocean are called estuaries.
  • The most commercially important and heavily populated estuaries are the
    mouths of major rivers.

Artesian Wells:

  • It is special type of well, which owing to the nature of its formation
    is quite distinctive.
  • Here, rock layers are down-folded into a basin shape so that permeable
    strata may be sandwiched between impermeable layers.
  • The impermeable layer below prevents the water from passing downwards
    while the impermeable layer on top prevents any possibility of water
    escaping upwards. Such a structural basin is called an aquifer.

  • Endogenetic Forces: The forces coming from within the earth are
    called endogenetic forces which cause two types of movements in the earth
    viz. (i) Horizontal movements and (ii) Vertical movements.
  • Exogenetic Forces: The exogenetic forces or
    processes, also called as denudational processes, or destructional forces or
    processes are originated from the atomosphere. They are also known as
    plantation processes. Denudation includes both weathering and erosion.

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