Inside Our Earth

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Topics in the Chapter

Planet Earth
Interior of the Earth

→ Crust

→ Mantle

→ Core

Rocks and their Types

→ Igneous rocks

→ Sedimentary rocks

→ Metamorphic rocks

Use of Rocks
Rock Cycle
Minerals

Planet Earth

The earth in which humans live is not absolute spherical in shape.

Interior of Earth

The earth is like onion which is made up of several layers.

Layers of the Earth

Crust

The uppermost layer over the earth’s surface is called the crust.
It is the thinnest of all the layers.

→ It is 35 km thick on the landmass (continental masses) and only 5 km on the ocean floors.

Main mineral constituents of the continental mass: Silica and Alumina.

→ Thus, it is called sial (si-silica and al-alumina).

The oceanic crust mainly consists of silica and magnesium.

→ Thus, it is called sima (si-silica and ma-magnesium).

Mantle

This layer extends up to a depth of 2900 km below the crust.

Core

The innermost layer is the core.
The radius of core is about 3500 km.
It is mainly made up of nickel and iron.

→ Thus, it is called nife (ni – nickel and fe – ferrous i.e. iron).

The central core has very high temperature and pressure.

Rocks

Any natural mass of mineral matter that makes up the earth’s crust is called a rock.
It can be of different colour, size and texture.
There are three major types of rocks:

→ Igneous rocks

→ Sedimentary rocks

→ Metamorphic rocks

Igneous Rocks

When the molten magma cools, it becomes solid and is called igneous rock.
They are also called primary rocks.
Two types of igneous rocks:

→ Intrusive rocks

→ Extrusive rocks

When the molten lava comes on the earth’s surface, it rapidly cools down and becomes solid on the crust.

→ They have a very fine grained structure.

→ Example: Basalt. The Deccan plateau is made up of basalt rocks.

When the molten magma cools down deep inside the earth’s crust it forms intrusive igneous rocks.

→ Since they cool down slowly they form large grains.

→ Example: Granite. Grinding stones are made of granite.

Sedimentary Rocks

Rocks break into small fragments called sediments.
These are transported and deposited by wind, water, etc., and form sedimentary rocks.

→ Example: Sandstone is made from grains of sand.

They may also contain fossils of plants and animals.

Metamorphic Rocks

Under great heat and pressure, Igneous and sedimentary rocks change into metamorphic rocks.

→ Example: Clay changes into slate and limestone into marble.

Use of Rocks

Used for construction like buildings and roads.
They are source of useful minerals.

Rock Cycle

The process of transformation of rock from one type to another is called rock cycle.
It describes changes among Igneous, Sedimentary and Metamorphic rocks.

→ When the molten magma cools, it solidifies to become igneous rock.

→ These rocks break into small particles by weathering and form sedimentary rocks.

→ Smaller grains move to basins and form layers of sedimentary rocks.

→ These rocks under heat and pressure become metamorphic rocks.

→ Metamorphic rocks under extreme heat melt to become magma again.

→ The magma cools and solidifies again to form igneous rocks.

Note: These processes take hundreds and thousands of years.

Minerals

Minerals are naturally occurring substances with definite physical and chemical properties.
They are important to humans.
Examples: Coal, natural gas, petroleum, iron, aluminium, gold, uranium, etc.
They are used in industries, medicines, fertilisers and more.

MCQs

1. The innermost layer of the earth is

(a) Mantle

(b) Sima

(d) Core

► (d) Core

2. Red fort is made up of

(a) Red sandstone

(b) Black sandstone

(d) Black marble

► (a) Red sandstone

3. ____ rocks are hard where ____ rocks are soft.

(a) sedimentary, lava

(b) sedimentary, magma

(d) igneous, sedimentary

► (d) igneous, sedimentary

4. The molten magma cools down deep inside the earth's crust. Solid rocks so formed are called

(a) Intrusive Sedimentary rocks

(b) Intrusive Metamorphic rocks

(d) Intrusive igneous rocks

► (d) Intrusive igneous rocks

5. Lithosphere is

(a) Mantle

(b) Magma

(d) Crust

► (d) Crust

6. Which layer is having a radius of about 3500 km

(a) Sial

(b) Crust

(d) Mantle

► (c) Outer core

7. Fossils are the remains of dead _______

(a) Plants

(b) Animals

(d) None of the above

► (c) Both a and b

8. The remains of the dead plants and animals trapped in the layers of rocks are called

(a) Rocks

(b) Conventional

(d) Minerals

► (c) Fossils

9. The Taj Mahal is made of

(a) White marble

(b) Black marble

(d) Yellow marble

► (a) White marble

10. Like an onion, the Earth is made up of several concentric layers (one inside the other). What is the uppermost layer of Earth called?

(a) Mantle

(b) Core

(d) Magma

► (c) Crust

11. Sandstone is made from

(a) Grains of soil

(b) Grains of plants

(d) Grains of sand

► (d) Grains of sand

12. The main mineral constituents of the continental mass are

(a) Silica and alcohol

(b) Silver and alcohol

(d) Silica and alumina

► (d) Silica and alumina

13. When magma from deep below forces its way up to earth's surface, it is called

(a) Sand

(b) Marble

(d) Volcano

► (d) Volcano

14. Thinnest layer of the earth is

(a) Crust

(b) Nife

(d) Mantle

► (a) Crust

15. Which type of rocks is called primary rocks

(a) Fossils

(b) Igneous

(d) Sedimentary

► (b) Igneous

16. Rocks roll down, crack, and hit each other and are broken down into small fragments. These smaller particles are called

(a) Sediments

(b) Sand

(d) Units

► (a) Sediments

17. There are three major types of rocks except

(a) Metamorphic rocks

(b) Sedimentary rocks

(d) Mantle rocks

► (d) Mantle rocks

18. Silica and magnesium are the constituents of

(a) Rock

(b) Inner Core

(d) Mantle

► (d) Mantle