NCERT Solutions for Class 7 Social Science Geography Chapter 2 Inside Our Earth (अध्याय 2: हमारी पृथ्वी के अंदर) free to View online. All the NCERT Solutions are based on latest NCERT Books for the academic session 2019 – 20.
NCERT Solutions for Class 7 Social Science Geography Chapter 2
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Inside Our Earth: Question answers
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7 Social Science – Geography – Chapter 2: Question Answers
Important Notes on Chapter 2
The uppermost layer over the earth’s surface is called the crust. It is the thinnest of all the layers. It is about 35 km. on the continental masses and only 5 km. on the ocean floors. The oceanic crust mainly consists of silica and magnesium; it is therefore called sima (si-silica and ma-magnesium).
The innermost layer is the core with a radius of about 3500 km. It is mainly made up of nickel and iron and is called nife (ni – nickel and fe – ferrous i.e. iron). The central core has very high temperature and pressure.
Any natural mass of mineral matter that makes up the earth’s crust is called a rock. Rocks can be of different colour, size and texture. 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.
When 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. Sometimes the molten magma cools down deep inside the earth’s crust. Solid rocks so formed are called intrusive igneous rocks.
Rocks roll down, crack, and hit each other and are broken down into small fragments. These smaller particles are called sediments. These sediments are transported and deposited by wind, water, etc. These loose sediments are compressed and hardened to form layers of rocks. These types of rocks are called sedimentary rocks. For example, sandstone is made from grains of sand. These rocks may also contain fossils of plants, animals and other microorganisms that once lived on them.