Before introducing the topic 'extrusive igneous rocks' the following topics are necessary to be covered: i) Lava ii) Interior of the Earth Important Points Interior of the Earth: The earth is made up of several concentric layers with one inside another. The interior of the earth can be divided into 3 different layers – crust, mantle, and core. The uppermost layer over the earth’s surface is called the crust. The earth’s crust is made up of various types of rocks. Just beneath the crust is the mantle which extends up to a depth of 2900 km. below the crust. The innermost layer is the core with a radius of about 3500 km. It is mainly made up of nickel and iron. Lava: Lava is actually fiery red molten magma coming out from the interior of the earth on its surface. Once the students are clear about the interior of the Earth and meaning of lava, then it will be easy for them to understand about the topic 'extrusive igneous rocks'. There are three major types of rocks: igneous rocks, sedimentary rocks and metamorphic rocks. When the molten magma cools, it becomes solid. Rocks thus formed are called igneous rocks. They are also called primary rocks. There are two types of igneous rocks: intrusive rocks and extrusive rocks. Extrusive igneous rocks: ​When the molten lava comes on the earth’s surface, it rapidly cools down and becomes solid. Rocks formed in such a way on the crust are called extrusive igneous rocks. They have a very fine grained structure. For example, basalt. The Deccan plateau is made up of basalt rocks. Hence, we can conclude that the following topics are necessary to be covered BEFORE introducing the topic 'extrusive igneous rocks' i) Lava ii) Interior of the Earth