UPSC CIVIL SERVICES RESULT 2015-2016

INSIDE OUR EARTH NOTES FOR IAS PRELIMS 2015

                                   Inside Our Earth

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Earth
  • The earth is divided into many concentric layers with one inside another.
  • These concentric layers are differentiated from each other  physically and chemically.
  • Earth’s outermost layer is crust where we  live, middle layer is mantle highly viscous, innermost layer core -it has two parts outer core which is  in a liquid form and inner core which is solid.
Structure Of The Earth

Three Layers of the Earth-Crust, Mantle and Core (outer core and Inner core).

Crust-Outermost or topmost layer of the earth is called crust.
  • Crust is thinnest layer among all other layers which is mantle and core.
  • Crust is fragmented into many plates which floats on mantle (second layer of the earth) Earthquake occurs when this huge plates comes closer and hit each other.
  • Plate tectonic theory explains the motions of these plates.
  • The earth’s crust is mainly found in two forms Continental mass and Oceanic Crust.

Continental mass-Silica and Aluminium are the main mineral component of the continental mass. Continental mass is thus called Sial (Si =silica and al =aluminium or alumina)


Oceanic Crust-Silica and Magnesium are the main mineral components of the oceanic crust .Continental crust is therefore called Sima (Si=silica and ma=magnesium)


Mantle-The second layer of the earth
  • It is under the crust and extends upto a depth of 2900 km.
  • Mantle have mainly silicate rocks which is rich in Iron and magnesium
  • Mantle is the thickest layer of the earth.

Core-Core is the innermost layer of the earth

The main mineral components of the core are nickel and Iron thus it is called Nife (Ni=nickel and Fe-ferrous(iron)).
  • Core has a radius of about 3500 km.
  • Core is divided into two parts  inner core and outer core .
  •  Core has very high temperature and pressure.

Inner core
  • The inner core was discovered in 1936 by Inge Lehmann
  • Inner core is solid (may be inner core is not a solid, but, because it is able to deflect seismic waves, it is regarded as solid)
  • The inner core has a radius of about about 1,220 km.

Outer core
  • Outer core-It surrounds the inner core.
  • Outer core is liquid and mainly consists of nickel and iron.
  • Outer core is about 2,1880 km thick.

                           Rocks and Minerals

A rock is a naturally occurring solid aggregate of mineral matter.
Rocks can be of different texture, colour and size.

3 Major types of rocks

Types of rocks with example

There are mainly three types of rocks Igneous rocks, Sedimentary rocks and metamorphic rocks.

                            Igneous rocks

Latin word Ignis =fire.


  • Igneous rocks form from volcanic magma when a volcano erupts and are also referred to as volcanic rocks. When the molten magma cools it becomes igneous rocks.

Igneous rocks are of two types –Intrusive rocks and extrusive rocks

Intrusive rocks-When molten magma cools down beneath the earths crust it forms intrusive rocks. Intrusive rocks form from molten material (magma) that flows and solidifies underground.

Examples of intrusive rocks- Granite, Diorite.

Extrusive rocks-When the molten magma comes out of the earth’s surface and cools down it forms extrusive rocks.

Examples of extrusive rocks – Rhyolite, Andesite, Basalt etc

                            Sedimentary rocks

When the rocks break down into small pieces these ,small fragment are transported by wind,water .These compressed and hardened to form sedimentary rocks.

  • Erosion and deposition plays a major role in the formation of sedimentary rocks.
  • Sedimentary rocks are also called secondary rocks.      

Examples of sedimentary rocks- Shale, Sandstone, Limestone, Conglomerate etc

                             Metamorphic rocks

 Metamorphic rocks are any rock type that has been altered by heat, pressure, and/or the chemical action of fluids and gases.

Igneous and sedimentary rocks can be converted into metamorphic rocks under great heat , pressure and chemical reaction.

Example-limestone changes into marble.

Examples of Metamorphic rocks- Slate, Quartzite, Schist, marble.

              Rock cycle

Any type of rocks changes into another type under heat, pressure, chemical change and other conditions. This conversion of rocks from one type to another is called rock cycle.


Rock Cycle
Example-Molten magma cools to form igneous-These igneous rocks breaks to form sedimentary rocksunder certain conditions sedimentary rocks converted into metamorphic rocks-These metamorphic rocks under great heat and pressure below the earth melts to form magma-These magma again when comes out on the earth surface forms igneous rocks.
Above process goes on and on several times, thus these process is called rock cycle.
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