NCERT Revision notes for class 7 Geography Inside our earth

Interior of the earth

The earth is made of three major layers:

1. Crust
2. Mantle
3. Core

Crust

The topmost layer of the earth surface is called crust. It is about 35 km long. Silica and Alumina are the major minerals found in this layer.

Mantle

The second layer of the Earth's surface is called mental it is about 2900 km in height.

Core

The last layer of the earth's surface is called core. It is about 3500 km in height. There are are two parts of core outer Core and inner core. The major mineral found here are Nickel and iron.

Rocks and minerals

Rocks are the naturally occurring substance, which are formed of fixed chemical composition. There are major three types of Rock:

1. Igneous rock
2. Sedimentary rock
3. Metamorphic rock

Igneous rock

Igneous rocks are formed by the molten magma. When the molten Magma comes out of the volcano, it cools down slowly and turns into igneous rock. There are mainly two types of igneous rock:

1. Intrusive igneous rocks: When molten magma cools down inside the earth’s surface and become solid is called intrusive igneous rocks.
2. Extrusive igneous rocks: When the molten magma coos down on the surface of the earth and become solid is called extrusive igneous rock.

Sedimentary rock

When igneous rock rolls down and breaks into fragments, these fragments are called sediments. When these sediments are compressed together, they form sedimentary rock.

Example: Sandstone

Metamorphic rock

Igneous and sedimentary rocks are transformed into metamorphic rocks when they go under high temperature and pressure.

Example: Marble

Rock cycle

The process of conversion of one rock to another is known as Rock cycle.

Related NCERT Revision notes

• Environment