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CLASS VII GEOGRAPHY (The Surface and Interior of the Earth)

 D. Answer the following questions in brief.

1. What is the special feature of sedimentary rocks?

Answer: Sedimentary rocks are layered.

2. How are metamorphic rocks formed?

Answer: Rocks which originally are igneous or sediment in nature get changed in the metamorphic rocks due to the heat and pressure.

3. What is lava?

Answer: The fine red molten magma coming out from the interior of the earth on its surface is called lava.

4. Why are igneous rocks called the primary rocks?

Answer: Igneous rocks are called the primary rocks as they were formed first over the earth surface.

5. What are sediments?

Answer: The weathering process breaks the rocks into small pieces. These are then carried away by water and then deposited on the river beds or sea beds, these deposits are called sediments.

E. Answer the following questions.

1. Differentiate between the P-Wave and the S-Wave.

Answer: The P-Wave or primary wave which can travel through both solid and liquid mediums and is faster in speed. Whereas, the S-Wave or secondary wave can pass through only a solid medium at a slower speed.

2. Write two characteristics of each of the following:

(a) Crust (b) Mantle (c) Core

Answer: two characteristics of Crust, Mantle and Core are:

(a) Crust

  • Crust is the uppermost layer over the earth’s surface.
  • It is the thinnest of all the layers.

(b) Mantle

  • Mantle is a very thick layer of rocks.
  • It lies just beneath the crust.

(c) Core

  • Core is the innermost layer of the earth.
  • It is mainly made up of nickel and iron.

3. What are fossil fuels? Name any two fossil fuels and specify their importance.

Answer: The remains of animals and plants get buried and trapped under the layers, and over a period of time get converted into coal, oil and natural gas. They are called fossil fuels.

Oil and natural gas are the two fossil fuels. They have great economic importance all over the world as they are a major source of energy.

4. Why is the knowledge of the earth’s interior based on indirect observation?

Answer: The intensive heat neither allows us to dig deep nor is there any possibility of living organisms deep inside the earth. It is therefore, we have little knowledge about the earth’s interior. Whatever knowledge we have, is based on indirect observation.

5. What are minerals? On what basis can the minerals be identified? Give examples.

Answer: A naturally occurring substance that have a definite chemical composition is called a mineral.

They are identified on the basis of their colour, hardness and lustre. Diamond, gold and silver are some of the examples of minerals.

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