The earth, our homeland, is a dynamic planet. It is constantly undergoing changes, inside and outside. The earth is made up of several concentric intricate layers, just like an onion. Its three layers are: Outer shell: Crust Middle shell: Mantle Inner shell: Core The Crust is the outermost and the thinnest layer, which covers the mantle. It comprises of 0.5% of the volume of earth, and it is the hard shell on which we live.

The Mantle lies between the crust and the core. Its thickness is 2,900 km and it is highly viscous. It comprises of 83% of the volume of earth. The Core is the innermost and the hottest layer of earth. It is composed of Nickel (Ni) and Iron (Fe) and comprises of 16% of the volume of earth. We’ll also learn about rocks in this chapter. Any natural mass of mineral matter that makes up the crust of the earth is called rock. Rocks can be hard or soft, as small as a grain or as large as a building. There are mainly three types of rocks:

1. Igneous Rocks - These are formed by the solidification of the molten material that originated within the earth. They are classified on the basis of texture.

2. Sedimentary Rocks - These are formed from the material derived from other rocks and are laid down under water.

3. Metamorphic Rocks - These are formed as a result of transformation of sedimentary and igneous rocks, when they are subjected to high temperature and great pressure in the interior of the earth.

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