.png)
The earth, our homeland is a dynamic planet. It is constantly undergoing changes inside and outside. Have you ever wondered what lies in the interior of the earth? What is the earth made up of?
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 main mineral constituents of the continental mass are silica and alumina. It is thus called sial (si-silica and al-alumina). The oceanic crust mainly consists of silica and magnesium; it is therefore called sima (si-silica and ma-magnesium)
Let`s see video to understand these which we saw already in the Smart classroom.
1. Structure of the earth
2. Inside the earth
You will be surprised to know that one type of rock
changes to another type under certain conditions in a
cyclic manner. This process of transformation of the rock
from one to another is known as the rock cycle. You
have already learnt when the
molten magma cools; it solidifies
to become igneous rock. These
igneous rocks are broken down
into small particles that are
transported and deposited to
form sedimentary rocks. When
the igneous and sedimentary
rocks are subjected to heat
and pressure they change
into metamorphic rocks. The
metamorphic rocks which are still
under great heat and pressure
melt down to form molten magma.
This molten magma again can
cool down and solidify into
igneous rocks.
Do You know?
The deepest mine in the world, is in South Africa. It is about 4 km. deep. In search for oil engineers have dug a hole about 6 km. deep. • To reach to the centre of the earth (which is not possible!) you will have to dig a hole 6000 km. deep on the ocean floor.
