'Inside Our Earth' Geography (Chap-2) class-7

Geography (Chap-2)                         Inside Our Earth

Ø  The radius of the earth is  about 6371 kms.

Ø  The earth, a dynamic planet is constantly undergoing changes inside and outside of it.

Ø  Just like an onion, the earth is made up of several concentric layers with one inside another.

Ø  The uppermost and the thinnest layer over the earth’s surface is called the Crust.

Ø  The Crust is about 35km on the continental masses and only 5km on the ocean floors.   

Ø  The main mineral constituents of the continental mass are Silica and Alumina(Sial).

Ø  The oceanic crust mainly consists of Silica and Magnesium(Sima).

Ø  Just beneath the crust is the Mantle which extends upto a depth of 2900km below the crust.

Ø  The Crust forms only 1% of the volume of the earth, 84% consists of Mantle and 15% makes the Core.

Ø  The innermost layer is the Core with a radius of about 3500km. Made up of Nickel & Iron (Nife).

Ø  The central Core has very high temperature and pressure.

Ø  The earth’s Crust is made up of various types of rocks.

Ø  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.

Ø  There are 3 major types of rocks: Igneous rocks, Sedimentary rocks & Metamorphic rocks.

Ø  When the molten magma cools, it becomes solid. Rocks thus formed are called Igneous rocks.

Ø  The word ‘Igneous’ is derived from the Latin word ‘Ignis’ means fire.

Ø  There are two types of igneous  rocks: Intrusive and Extrusive rocks

Ø  When the molten magma comes out from the interior of earth to its surface, it cools down rapidly and becomes solid. Such way of rock forming is called Extrusive Igneous rock. Ex- Basalt

Ø   Extrusive Igneous rocks have a very fine grained structure.

Ø   Deccan plateau of India is up made by Basalt rocks.                   

Ø  When the molten lava cools down deep inside the earth’s crust it is called Intrusive Igneous rocks.

Ø  As intrusive igneous rocks cool down slowly and they form large grains. Example- Granite

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

Ø  Sedimentary is derived from the Latin word ‘sedimentum’ means settle down.

Ø  The sediments are transported and deposited by wind, water etc. These loose sediments are compressed and hardened to form layers of rocks called ‘sedimentary rocks’. Ex- Sandstone

Ø  Both Igneous and Sedimentary rocks change into Metamorphic rocks under great heat and pressure. For example- Clay changes into Slate and Limestone changes into Marble.

Ø  Metamorphic is derived from the Greek word ‘Metamorphose’ means change of form.

Ø  Fossils: The remains of the dead plants and animals trapped in the layers of rocks.

Ø  The Red Fort of India made up of Sandstone while the Taj Mahal is made up of white Marble.