NCERT Solutions for Class 7 Social Science Chapter 12 - Interior of the Earth

Question 1:

What are the three layers of the earth?


The earth is made up of three concentric layers. The outermost layer, which covers the earth like a skin is called the crust. The crust is the thinnest among all the layers. The layer beneath the crust is called the mantle. The thickness of the mantle is 2,900 kilometres. It is the deepest and most inaccessible zone of the earth. It extends from the lower boundary of the mantle (2,900 km) to the centre of the earth (6,371 km).

Question 2:

What is rock?


A rock can be defined as an aggregate of minerals. Earth is made up of rocks and minerals. Rocks can be of different colour, size and texture.

Question 3:

Name three types of rocks.


The three types of rocks are Igneous, Sedimentary and Metamorphic.

Question 4:

How are extrusive and intrusive rocks formed?


Extrusive rocks are formed when the molten material comes on the earth’s surface, cools rapidly and solidifies. Sometimes, the molten material cools down deep inside the earth. The rocks formed in this way are called instrusive rocks.

Question 5:

What do you mean by a rock cycle?


It is a continuous process through which old rocks are transformed into new ones. It helps us to understand the origin of igneous, sedimentary and metamorphic rocks.

Question 6:

What are the uses of rocks?


Rocks are very useful to us. Roads, houses and buildings are made of hard rocks. Some rocks hold reserves of coal, oil and natural gas. Rocks are rich in minerals and other valuable substances.

Question 7:

What are metamorphic rocks?


A rock which has been changed from its original form by heat or pressure. Metamorphism may involve both physical as well as chemical changes in the characteristics of the pre-existing rocks.

Question 8:

We cannot go to the centre of the earth. Give reasons.


The temperature at the centre of the earth is extremely high, which is about 6000°C. The density of rocks in this part is highest. Such conditions restrict the direct approach to the interior of the earth.

Question 9:

Sedimentary rocks are formed from sediments. Give reasons.


These rocks are formed through consolidation of sediments deposited in water bodies like, rivers, lakes and seas. Over a period of time, a significant thickness of sediments accumulates and consolidates to form hard rocks.

Question 10:

Limestone is changed into marble. Give reasons.


Limestone is changed into marble under great heat and pressure of the above layers of the rocks. The newly formed rocks are very hard and have close-banded structure.