(i) The three layers of the earth are
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Crust
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Mantle
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Core
(ii) Any natural mass of mineral matter that makes up the earth’s crust is called a rock. The earth’s crust is made up of various types of rocks of different textures, sizes and colours.
(iii) The three types of rocks are
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Igneous Rocks
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Sedimentary Rocks
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Metamorphic Rocks
(iv) The molten lava comes out of volcanoes, reaches the earth’s surface and cools down rapidly to become a solid piece of rock. This is how extrusive rocks are formed. For example, basalt.
When the molten lava solidifies deep inside the earth’s crust, the rocks so formed are called intrusive rocks. For example, granite.
(v) The process of transformation of rocks from one type to another due to changes in certain conditions in a cyclic manner is called a rock cycle.
(vi) Rocks are useful for various purposes, such as
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They help in making roads.
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They are used in the construction of houses and buildings.
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Small stones are used by children in different types of games.
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They are used in fertilisers.
(vii) The type of rocks formed when igneous and sedimentary rocks experience heat and pressure are called metamorphic rocks.