Here is the notes for Class 7 NCERT Geography – Chapter 2: Inside our Earth

 

Interior of the Earth

  • The earth is made up of several concentric layers with one inside another .

Crust

  • 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
  • The oceanic crust mainly consists of silica and magnesium; it is therefore called sima.

Mantle

  • It is just beneath the crust.
  • It extends up to a depth of 2900 km.

Core

  • The innermost layer is the core with a radius of about 3500 km.
  • It is mainly made up of nickel and iron and is called nife.
  • The central core has very high temperature and pressure.

Volume of the Earth

  • Crust- 1%
  • Mantle- 84%
  • Core- 15%

Radius of the Earth- 6371 km.

ROCKS AND MINERALS

  • The earth’s crust is made up of various types of rocks.
  • 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
        • Extrusive rocks
          • When the molten magma 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
          • example, basalt (Deccan plateau is made up of basalt rocks)
        • Intrusive 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.
          • Example, Granite

Sedimentary rocks

  • Rocks roll down, crack, and hit each other and are broken down into small fragments called sediments.
  • These sediments are transported and deposited by wind, water, etc.
  • These loose sediments are compressed and hardened to form layers of rocks known as Sedimentary rocks.
  • This rocks contains fossils of plants, animals and other micro-organisms that once lived on them.
  • Example, sandstone is made from grains of sand.

Metamorphic rocks

  • Igneous and sedimentary rocks can change into metamorphic rocks under great heat and pressure.
  • Example, clay changes into slate and limestone into marble.

Rock cycle

  • The process of transformation of the rock from one to another is known as the rock cycle.

Steps of the rock cycle

  • When the molten magma cools; it solidifies to become igneous rock.
  • These igneous rocks are broken down into small particles that are transported and deposited to form sedimentary rocks.
  •  When the igneous and sedimentary rocks are subjected to heat and pressure they change into metamorphic rocks.
  • The metamorphic rocks which are still under great heat and pressure melt down to form molten magma. This molten magma again can cool down and solidify into igneous rocks .

Minerals

  • Rocks are made up of different minerals.
  • Minerals are naturally occurring substances which have certain physical properties and definite chemical composition.
  • Example, coal, petroleum, gold, silver, fertilisers, etc
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