Page 102 - SST Class 07

Inside the Earth 14

q Layers of the earth q Rocks
q Rock cycle q Minerals

Introduction two chief elements in the continental crust are
silicon and aluminium, also called SIAL , and the
Earth is a unique planet which is constantly
two chief elements in the oceanic crust are silica
undergoing changes. What is the structure of this
and magnesium, also called SIMA . Its average
planet? What lies inside its crust? What is its density is less than 3 which increases with the
interior made up of?
depth. It is the most important layer as it sustains
It is not possible to undertake direct study about the life. This layer undergoes constant changes.
earth’s interior to know all this because we cannot Mantle
reach there. Our knowledge about it has to be based
on the observations of seismic or earthquake waves Under the crust lies the mantle, which is about
pattern. The interior of the earth is not composed of 2,900 km thick. It is mostly solid, but at its top,
the same material. Its density gradually increases some rocks are molten or semi-molten.
from the surface towards the centre. Core

The core is the innermost layer. It can be divided
LAYERS OF THE EARTH
into two parts—the outer core and the inner core .
The earth is like a sphere, more like a pear, The inner core is composed of nickel and iron,
bulging a little at the Equator. Its radius is about also called NIFE. It is solid. It is due to the
6,367 km. The inside of the earth is made of presence of iron and nickel in the core that the
several layers or concentric shells, one below the earth acts like a magnet. The inner core is
other, much like an onion. These layers are made surrounded by the outer core. The outer core is
up of different materials. We can divide these liquid and is about 2,100 km thick.
layers into three main layers—crust mantle and
,
core .
Info Bits
Info Bits
Crust
The crust forms only 0.5 percent of the total
The outermost layer of
volume of the earth, about 16 percent of its
the earth is called the Crust volume is the mantle and about 83 percent is the
crust. It is the thinnest Mantle
Outer Core core.
of all layers. Its average Inner Core
thickness varies from 6 The density and temperature of the earth increases
to 40 km. It is thicker with depth; the deeper it is, the denser and hotter
in the continents and it is. Temperature rises at the rate of 1°C for every
thinner in the ocean 32 metres. It is possible that the temperature at the
beds. It is made up of Layers of the earth core is as high as 5,000°C, due to which all
rocks and soils. The material there is in the molten state. This molten
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