NCERT Book Class 7 Social Science (Geography) Chapter 3 Our Changing Earth

3 Our Changing Earth
Activity The lithosphere is broken into a number of plates known
as the Lithospheric plates. You will be surprised to know
Take a small coloured that these plates move around very slowly – just a few
paper pellet and put it
millimetres each year. This is because of the movement
in a beaker
half filled of the molten magma inside the earth. The molten magma
with water. inside the earth moves in a circular manner as shown in
Place the the activity.
beaker on a The movement of these plates causes changes on the
tripod stand surface of the earth. The earth movements are divided
and heat it. As the on the basis of the forces which cause them. The forces
water warms up, you which act in the interior of the earth are called as
will observe that the Endogenic forces and the forces that work on the surface
paper pellet is moving
of the earth are called as Exogenic forces (Fig. 3.1).
upward along with the
warm layers of water
and then Earth movements
sinks back
along with Endogenic forces Exogenic forces
the cooler
layers of water. The Sudden forces Diastrophic forces Erosional and Depositional
molten magma inside
the earth moves in a
similar manner. Earthquake Building mountains River

Volcano Wind

Glossary
Landslides Sea-waves
Lithospheric plates:
The earth’s crust Glaciers
consists of several
large and some small, Fig. 3.1: Evolution of Landforms
rigid, irregularly-
shaped plates (slabs) Endogenic forces sometimes produce sudden movements
which carry and at the other times produce slow movements. Sudden
continents and the movements like earthquakes and volcanoes cause mass
ocean floor. destruction over the surface of the earth.