Page 146 - SST Class 06

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Major Relief Features
of the Earth
The earth is an enormous place. There is so
much that we don’t yet know about what hap-
pens on the surface of the earth, so how could
we possibly know about what happens deep
down below the earth’s surface? Scientists are
still working out some of the details, but with the
help of equipment used when studying earth-
quakes, they know the earth is made up of
layers. Atmosphere
Crust
Mantle
Outer core
Outer core of
molten metal
Solid metal
inner core
Layers of the Earth
THE CORE
Let’s start at the very center of the earth. The
word ‘core’ means the central part of something,
for example, an apple has a core. The earth has
an inner core and an outer core. Scientists think
that the inner core is solid and mainly made of
iron. Iron is very hard – that’s why knights used it
to make their armor. The outer core is also
mostly iron, but this layer is liquid (melted) iron.
THE MANTLE
The next layer is called the mantle. It is made of
rock. It is very hot in this part of the earth,
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causing the rock to behave a little bit like a liquid
and a solid.
THE CRUST
The crust is the part of the earth that we walk on.
Compared to the other layers, it is quite thin and
breakable. You can think of the crust of the earth
as being a bit like the crust of a pie – although
this crust is 5–70 km deep depending on whether
you are under the ocean or on top of a moun-
tain! The earth’s crust is not one continuous
surface like on a tennis or soccer ball. The crust is
‘broken’ into enormous pieces called tectonic
plates.
TECTONIC PLATES
Scientists think that the crust of the earth is made
up of six large (major) tectonic plates and a few
smaller ones. These plates fit together like puzzle
pieces and float on the partially molten mantle.
They slowly move and bump against each other
at a rate of a few millimeters to up to 20 cm per
year. It is this bumping and rubbing that causes
earthquakes and volcanoes.
The surface of the earth is neither even nor
regular. There are differences in elevation and
slope of various landforms both at the global
level as well as the local levels. This difference in
elevation and slope of landforms in a particular
area is known as relief. The relief at global level
can be categorised into two types — continents
and oceans. On the continents are found moun-
tains, plateaus, plains, lakes, etc. They are
termed as landforms. Deep under the ocean
waters are towering mountains, vast plateaus,
plains and deep trenches. They are termed as