NCERT Solutions for Class 7 Social Science Our Environment Chapter 2 Inside Our Earth

(i) The three layers of the Earth are the crust, the mantle and the core.

(ii) A rock refers to any natural mass of mineral matter that makes up the Earth’s crust.

(iii) Igneous, sedimentary and metamorphic rocks are the three types of rocks.

(iv) Extrusive rocks are formed when the molten magma present inside the Earth’s interior comes out onto the Earth’s surface, cools down and becomes solid. When molten magma cools down and solidifies deep within the Earth’s crust, intrusive rocks are formed.

(v)The transformation of one type of rock into another, under certain conditions and in a cyclical manner is referred to as the rock cycle. For example, igneous rocks, formed as a result of the solidification of molten magma, may break down into small particles, which may then be transported and deposited to form sedimentary rocks. Sedimentary and igneous rocks transform into metamorphic rocks when subjected to heat and pressure. These metamorphic rocks may themselves get broken down to form sedimentary rocks, or they may melt under great heat and pressure to form molten magma, which would then once again solidify to form igneous rocks.

(vi) Some of the uses of rocks are as follows:

(a) For building roads, houses and buildings

(b) For making jewellery

(c) For cutting and drilling purposes

(d) The fossilised remains of plants and animals present in rocks help in scientific research.

(e) The different minerals that make up different rocks are used as fuels, medicines, fertilisers, and in various industries.

(vii) Metamorphic rocks are the rocks that get formed under great heat and pressure. Igneous and sedimentary rocks, when subjected to heat and pressure, get transformed into metamorphic rocks.