GEOGRAPHY

Just like an onion, the earth is made up of several concentric layers with one inside another 

The earth comprises three layers: crust, mantle and core. Constant changes take place inside as well as outside the earth.

The uppermost layer over the earth’s surface is called the crust. It is about 35 km thick on the continental masses and only 5 km thick on the ocean floor. It is made up of silica and alumina and thus called sial.

The oceanic crust mainly consists of silica and magnesium called sima. Just below the crust is the mantle up to an extent of 2,900 km.

Crust: The uppermost layer over the earth’s surface. It is very thin.

The innermost layer is the core with a radius of 3,500 km. As it is made of nickel and iron, it is called nife(ni-nickel and fe-ferrous i.e. iron). The central core has a very high temperature and pressure.

Rock: A rock is a natural mass of mineral matter that makes up the earth’s crust.

These rocks are formed by cooling and solidifying molten magma.

Extrusive igneous rock

Intrusive igneous rock

 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 called extrusive igneous rocks.

When the molten magma cools down deep inside the earth’s crust solid intrusive igneous rocks are formed.

When loose sediments are compressed and hardened, layers of rocks are formed. These types of rocks are known as sedimentary rocks.