NCERT Class 7 Geography Chapter 2 - Inside our Earth Notes

Chapter 2 - Inside our Earth Notes

1. The uppermost layer over the earth’s surface is called the crust. It is the thinnest layer and its depth is about 40 km its range is about 35 km on the continental masses and only 5 km. on the ocean floors.

2. The earth’s crust is made up of various types of rocks. Any natural mass of mineral matter that makes up the earth’s crust is called a rock. Rocks can be of different colour, size and texture.

3. The main mineral constituents of the continental mass are silica and alumina. It is known as ‘sial’. The oceanic crust mainly consists of silica and magnesium. It is therefore known as ‘sima’.

4. Below the crust is the mantle which extends up to a depth of 2900 km.

5. In the earth, the innermost layer is the core with a radius of about 3500 km. It is mainly made up of nickel and iron and is called ‘nife’. The core has very high temperature and pressure.

6. There are three major types of rocks: igneous rocks (primary rocks), sedimentary rocks and metamorphic rocks.

7. Igneous rocks further can be divided as Intrusive rocks and Extrusive rocks.

8. Rocks roll down, crack, and hit each other and are broken down into small fragments. These smaller particles are called sediments. These sediments form sedimentary rocks.

9. Rocks are very useful to us. The hard rocks are used for making roads, houses and buildings.

10. Under certain conditions, one type of rock changes to another type in a cyclic manner. This process of transformation of the rock from one to another is known as the rock cycle.

11. The deepest mine in the world, is in South Africa. It is about 4 km deep. In search of oil engineers have dug a hole about 6 km deep.

12. To reach the centre of the Earth which is impossible you will have to dig a hole 6000 km deep in the ocean floor.

13. The crust forms only 1% of the volume of the Earth, 84% consists of the mantle and 15% makes the core.

14. The radius of the Earth is 6371 km.

15. The word Igneous is derived from the Latin word Ignis which means fire.

16. The word Sedimentary is derived from the Latin word sedimentum which means settle down.

17. The word Metamorphic is derived from the Greek word metamorphose which means change of form.

18. Fossils are the remains of dead plants and animals trapped in layers of rocks.

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