Short and Long Question Answers - Inside Our Earth - Social Studies (SST) Class 7

Short Q & A :

Ques 1: What are the uses of rocks?

Ans: Rocks are very useful to man, used for making roads, houses and building. Rocks are the source of precious metals like gold, silver, and platinum. We use stone in many games. For example, seven stone, top scotch, five stones

Ques 2: Define fossil.

Ans: The remains of dead plants and animal beneath the layer of rocks are called fossils.

Fig: Fossil

Ques 3: What is mantle?

Ans: It is an intermediate layer lies between the crust and the core of the earth .Its avg thickness is about 29,00 km. It is believed to consist of solid ultra basic rocks, rich in iron and magnesium.

Ques 4: What do you know about the core?

Ans: The innermost part of the earth is known as the core. The thickness of whole layer comprising the outer and the inner core is 4671 km. The outer core starts at the depth of 2900 km, rich in iron and nickel.

Ques 5: What is the importance of outer crust to us?

Ans: The solidified outer crust of the earth is of great importance to us .This thin crust just like the skin of an apple, forms the stage on which human life and civilization have developed. It has the valuable soil and gives us most of our minerals.

Ques 6: What is mineral?

Ans: A mineral is a naturally occurring substance having a definite chemical composition and physical properties.

Fig: Sandstone

Ques 7: Give example of all the three major forms of rocks?

Ans: Igneous-granite, basalt
Metamorphic rocks- marble, slate, graphite
Sedimentary- limestone, sandstone.

Ques 8: What do you know about extrusive and intrusive rocks formed?

Ans: When the molten lava comes on earth’s surface; it rapidly cools down and become solid. Rocks formed in such a way on the crust are called Extrusive igneous rock. Sometimes molten magma cools down deep inside the earth crust, solid rocks so formed are called Intrusive igneous rocks.

Fig: Basalt

Ques 9: Define the following?

1. Igneous rocks

2. Sedimentary rocks

3. Metamorphic rocks

Ans: 

1. Igneous rocks: Igneous rocks are formed by the solidification of hot and molten magma, also termed as primary rocks or the parent rocks.
2. Sedimentary rocks: Sedimentary rocks are formed the sediments, particles, grains or fragments derived from existing primary rocks. These sediments are soft but in course of time they become hard and compact.
3. Metamorphic rocks: Because of tremendous pressure and high temperature both igneous and sedimentary rocks may be altered so greatly in appearance and composition that they entirely lose their original character. They are termed as metamorphic rocks

 Ques 10: Match the following-

Ans:

1-c

2-a

3-b

4-d

Ques 11: What is the source of knowing of the layered structure of the earth?

Ans: The layered structure of the earth has been known on the basis of variation in temperature, pressure and the density of the material in the interior. The behaviour in the earth quake shock waves travelling from the centre of their origin in all directions has been much helpful to this end.