NCERT Book Class 7 Social Science (Geography) Chapter 2 Inside Our Earth

2 Inside Our Earth

The earth, our homeland is a dynamic planet. It is
constantly undergoing changes inside and outside. Have
Do you know?
you ever wondered what lies in the interior of the earth?
What is the earth made up of? • The deepest mine in
the world, is in
INTERIOR OF THE EARTH South Africa. It is
Crust
Just like an onion, the Lithosphere about 4 km. deep. In
search for oil
earth is made up of Mantle
engineers have dug a
several concentric
Core-mantle hole about 6 km.
layers with one inside boundary deep.
another (Fig. 2.1). The • To reach to the
Inner core Outer
uppermost layer over core centre of the earth
the earth’s surface is (which is not
called the crust. It is the possible!) you will
thinnest of all the have to dig a hole
layers. It is about 35 km. 6000 km. deep on
on the continental the ocean floor.
masses and only 5 km. Fig. 2.1: Interior of the Earth
on the ocean floors.
The main mineral
constituents of the
Continental Oceanic
continental mass are Crust Continent Ocean Crust
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) (Fig. 2.2).
Just beneath the crust
is the mantle which
extends up to a depth of
2900 km. below the crust. Fig. 2.2: Continental Crust and Oceanic Crust