Inside Our Earth

Extra Questions

Very Short Answer Type Questions

Define crust.

Answer: The uppermost layer over the earth’s surface is called crust.

Which mineral is found in the core?

Answer: Nickel and iron

What is lava?

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

Which mineral is found in the crust?

Answer: Silicon, aluminum, magnesium

Arrange the following terms from top to bottom based on the order in which they appear in the interior of the earth: mantle, core and crust.

Answer: Crust, Mantle and Core


Which layer of the earth is the thinnest?

Answer: crust

List the minerals that are used as fuels?

Answer: Coal, natural gas, petroleum

Which factor is responsible for the difference between extrusive and intrusive rocks?

Answer: The place where the cooling of magma takes place is responsible for the difference between extrusive and intrusive rocks.

List the minerals that are used for industrial purposes?

Answer: Gold, aluminium, iron, uranium etc.

Why does granite have large grains?

Answer: The slow cooling down of the magma results in large grains in the rocks. Hence, granite has large grains.

Give an example of extrusive igneous rock.

Answer: basalt


Short Answer Type Questions

What are igneous rocks?

Answer: The rocks formed by the solidification, on the cooling of molten magma, are called igneous rocks. They are of two types – intrusive rocks and extrusive rocks.

What are minerals?

Answer: Naturally occurring substances which have certain physical properties and a definite chemical composition are called minerals. They are of a great use to mankind, both as a fuel and for industries.

What are sedimentary rocks? How are they formed?

Answer: Sedimentary rocks are one of the major types of rocks. These rocks are formed by the hardening and compression of sediments.

What are metamorphic rocks?

Answer: The rocks that are formed when the igneous and sedimentary rocks are subjected to great heat and pressure are called metamorphic rocks.


Long Answer Type Questions

Describe the interior of the earth.

Answer: The earth is made up of several concentric layers. The main three layers of the earth are as under:

  1. The crust: It is the outermost layer over the earth’s surface. It is the thinnest of all the layers and about 35 km on the continental masses and only 5 km on the ocean floors. The main minerals constituting the continental mass are – silica and alumina. The continental mass is also called ‘sial’. The main mineral constituents of the oceanic crust are –silicon and magnesium. The oceanic crust is called ‘sima’.
  2. Mantle: It is the layer just beneath the crust and extends up to a depth of 2900 km below the crust.
  3. The core: It is the innermost layer i.e. it is below the mantle. Its radius is about 3500 km. The core consists of outer core and inner core. It is mainly made up of – nickel and iron. The innermost layer is also called nife. The name ‘nife’ is derived from the word ‘ni’ from nickel and ‘fe’ from ferrous meaning iron. The temperature and pressure of the central core is very high.

What are rocks? Write in detail about their types.

Answer: Rocks are a natural mass of mineral matter that makes up the earth’s crust. They can be of different colour, size and texture. They are of the following types.

  1. Igneous rocks: The rocks formed by the solidification, on the cooling of molten magma, are called igneous rocks. Depending on where the molten magma cools, they are of the following types: Intrusive rocks and Extrusive rocks.
  2. Sedimentary rocks: These rocks are formed by the settling down of sediments. These sediments when compressed and hardened, form sedimentary rocks.
  3. Metamorphic rocks: These are the rocks that are formed when the igneous and sedimentary rocks change their form under the following two circumstances: great heat and pressure.

Write a short note on minerals.

Answer: Rocks are made up of different minerals. Minerals are naturally occurring substances. They are found on the crust and the core of the earth. They have certain physical properties and have a definite chemical composition. They are very important to humankind. They are used as fuels, for example – coal, petroleum and natural gas. They are used in industries for making medicines, fertlisers and many other items, e.g. iron, aluminium, gold, silver, etc.

Describe the rock cycle.

Answer: A cyclic manner is followed in transformation of one type of rock to another type under certain conditions. This process of transformation of rock from one to another is called the rock cycle. When the molten magma cools and solidifies, it forms igneous rocks. These 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 high heat and pressure, they change into metamorphic rocks. The metamorphic rocks that are still under great heat and pressure, they melt down to form molten magma. This molten magma cools down again and solidifies to form igneous rocks.



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