Inside Our Earth

(i) The three layers of the earth are:

• Crust
• Mantle
• Core

(ii) A rock is a natural mass of mineral matter that makes up the earth's crust.
Rocks can be of different colour, size and texture.
(iii) Three types of rocks are:

• Igneous rocks also known as primary rocks.
• Sedimentary rocks.
• Metamorphic rocks.

(iv) When the molten lava comes on the earth's surface, it rapidly cools down and becomes solid. Rocks formed in this way on the crust are extrusive igneous rocks.
Sometimes the molten magma cools down deep inside the earth's crust. Solid rocks so formed are actually intrusive igneous rocks.
(v) One type of rock changes to another type under certain conditions in a cyclic manner. This process of transformation of the rock from one to another is known as the rock cycle. Let's understand it through example—Igneous rocks change into sedimentary rocks. When the igneous and sedimentary rocks are subjected to heat and pressure, they change into metamorphic rocks. The metamorphic rocks which are still under great heat and pressure meet down to form molten magma. This molten magma again can cool down and solidify into igneous rocks.
(vi)  Hard rocks are used for making roads, houses and buildings. Stones are used in many games, such as seven stones (pitthoo), hopscotch (stapu/kitkit), Five stones (gitti).
(vii) When the igneous and sedimentary rocks are subjected to heat and pressure they change into metamorphic rocks. For example, clay changes into slate and limestone into marble.