Inside our Earth - Geography NCERT Notes for UPSC

Interior of the Earth

The interior of the Earth consists of Crust, Mantle and the Core.

• Crust: 
  • It is the uppermost layer over the Earth’s surface.
  • It is the thinnest of all the layers. 
  • It is about 35 km on the continental masses and only 5 km on the ocean floors. 
  • The main mineral constituents of the continental mass are Silica and Alumina. It is thus called SiAl (Si-Silica and Al-Alumina). The oceanic crust mainly consists of silica and magnesium; it is therefore called SiMa (Si-Silica and Ma-Magnesium).

• The Mantle: It extends up to a depth of 2900 km below the crust.
• Core: It is the innermost layer with a radius of about 3500 km. It is mainly made up of Nickel and Iron and is called NiFe (Ni-Nickel and Fe- Ferrous i.e. Iron). The central core has very high temperature and pressure. 

Rocks and Minerals

Any natural mass of mineral matter that makes up the Earth’s crust is called a rock. Rocks can be of different colour, size and texture.

Three major types of Rocks

• Igneous rocks: When the molten magma cools, it becomes solid. Rocks thus formed are called igneous rocks. They are also called primary rocks. There are two types of igneous rocks: Intrusive rocks and Extrusive rocks.
  • Extrusive igneous rocks: When this molten lava comes on the Earth’s surface, it rapidly cools down and becomes solid. Rocks formed in such a way on the crust are called extrusive igneous rocks. They have a very fine-grained structure. For example, Basalt. The Deccan plateau is made up of basalt rocks.
  • Intrusive igneous rocks: Sometimes the molten magma cools down deep inside the Earth’s crust. Solid rocks so formed are called intrusive igneous rocks. Since they cool down slowly, they form large grains. For example, Granite.

• Sedimentary rocks: These rocks are formed by broken-down small fragments of the rock which are transported and deposited by wind, water, etc.  These loose sediments are compressed and hardened to form layers of the rocks. For example, sandstone is made from grains of sand.
• Metamorphic rocks: Igneous and sedimentary rocks can change into metamorphic rocks under great heat and pressure. For example, clay changes into slate and limestone into marble.

Rock cycle

One type of rock changes to another type under certain conditions in a cyclic manner. This process of transformation of the rock from one to another is known as the Rock cycle.

Interesting Facts

• The deepest mine in the world, is in South Africa. It is about 4 km deep.
• The Crust forms only 1 per cent of the volume of the Earth, 84 per cent consists of the Mantle and 15 per cent makes the Core. 

The radius of the Earth is 6371 km.

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