Page 121 - SST Class 07
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Inside Our Earth
The earth is a dynamic planet because it is
Crust
constantly undergoing changes inside and
Mantle
outside. The earth is made up of several concen-
tric layers with one inside another. There are Outer Core
three types of layer— crust, mantle and core. The Inner Core
crust is the uppermost layer over the earth’s
surface which is about 35 km on the continental
masses and only 5 km on the ocean floors. The
mantle has been just beneath the crust, which is
extended up to a depth of 2900 km. below the
crust. The innermost layer is the core, with a Structure of the Earth
radius of about 3500 km. small plates, which ‘float’ on top of the mantle
beneath them. The plates themselves are made
up of 2 different types of crust, continental crust
under the land and oceanic crust under the sea.
Continental crust is thick (25-70 km) and light
because it is made of rocks with a low density.
Oceanic crust is thin (6-11km) and heavy
because it is made of rocks (mostly volcanic
rocks) that have a high density. The oceanic crust
covers 2/3 of the earth’s surface.
Mantle
Our Earth The mantle is the thickest layer of the earth at
2,900 km of thickness. It makes up nearly 80%
STRUCTURE OF THE EARTH
of the volume of the earth. The mantle itself is
The earth is made up of 4 different layers. Each divided into 2 layers, the upper and lower
have unique characteristics as described below. mantles and the heat within these layers drives
The diagram shows where each layer is located. convection currents. The upper mantle is
Crust semisolid rock called magma that flows slowly
The crust is the thinnest layer of the earth and is due to convection currents. It is less than
the layer we live on. It is made up of a variety of 1,000°C in temperature. The lower mantle is kept
rocks and can reach up to 70 km thick in places. solid due to pressure and is between 1,000°C –
The crust itself is divided into large chunks called 3,500°C. If you had to describe the mantle as a
tectonic plates. There are around 7 large and 12 whole, it is classed as a liquid.
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