Our Changing Earth – Class 7

Question. Explain about different layers of the interior of the earth.
Answer: The earth is internally divided into three layers, such as the crust, mantle and the core of the earth.

The crust:

  • The earth crust means the uppermost part of the earth.
  • In this crust all living beings are found.
  • The earth crust is mainly made up of Silicon (Si) and Aluminium (Al) known as ‘Sial’.
  • This layer is about 35 km in the continental part and 5 km in the oceanic part.
  • oceanic part of the crust is mainly made up of silicon and magnesium known as ‘sima’.


  • Just beneath the earth crust this mantle layer is situated.
  • This layer is extended up to 2900 km from the earth surface.
  • This layer is very hot.
  • Mantle layer is mainly made up of cromium, ferrous, silicon and magnesium etc.

The core:

  • Under the mantle core is the deepest layer of the earth.
  • This layer is mainly made up of  nickel and ferrous, known as ‘Nife’.
  • This layer is extends up to the depth of 6371 km.
  • It is the hottest layer of the earth.

Question. What do you mean by rocks? explain its classification.
Answer: Rocks are the combination of several minerals. This earth surface is made up of different kinds of rocks. Rocks are generally very hard. There are generally three types of rocks, which are as follows:

Igneous rocks: 
  • This rock is formed just after the formation of the earth. and hence this rock is called as the basic rocks.
  • Generally these rocks forms when the molten magma cools and become solid.
  • Igneous rocks are two types: intrusive and extrusive.
  • When igneous rocks forms under the earth surface, such type of rocks are called as intrusive rocks.Like granite is an example of intrusive igneous rock. and
  • When igneous rocks after the process on the earth surface is called as extrusive igneous rocks. Basalt is an example of extrusive igneous rock.

Sedimentary rocks:

  • After the creation of igneous rocks, various erosional process also start to erode these rocks. All the erosional materials of igneous rocks deposits on the low land areas. After that due to the high pressure and temperature forms hard rock. This type of rocks are called as sedimentary rocks.
  • Sandstone is an example of sedimentary rock.
  • This rocks may form biologically like coal formation.

Metamorphic rocks:

  • Due to the high pressure or temperature, when igneous or sedimentary rocks changes and forms a new type of rocks, they are called as metamorphic rocks.
  • For example granite changes into gneiss. or limestone changes into marble.
  • Metamorphic rocks are generally soft as compare to igneous or sedimentary rocks.

Question. Explain about rock cycle.
Answer: This is the cyclic process of transformation of rocks from one form to another. For example after the formation of igneous rocks eroded and form sedimentary rocks through the depositional materials. Then both types of rock may change into metamorphic rock and lastly again goes under the earth surface and become the part of magma or components of igneous rocks.

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