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Chapter 6 inSidE tHE EArtH

Earth is also known as the Terra. It is the third planet outward from the sun. It is the largest of
the solar system’s terrestrial planes, and the only planetary body that modern science confirms
as harbouring life. This planet formed around 4.57 billion years ago and shortly thereafter
acquired its single natural satellite, the Moon. Its dominant species is the human.

intErior of thE Earth

The earth is made up of three concentric layers of varying
thickness known as the Crust, the Mantle and the Core.

1. crust

The surface layer of the earth is known as the crust. It
consists of the thinnest of all the layers of about 35 km on
the continental masses and only 5 km on the ocean floors. Interior of the Earth

The continental mass mainly consists of silica and alumina. It is thus called sial (si – silica
and al–alumina) whereas the oceanic crust mainly consists of silica and magnesium; it is,
therefore, called sima (si–silica and ma– magnesium).

2. maNtlE

The mantle, which is the second layer, extends upto a
depth of 2900 km below the crust. It is made up of iron,
magnesium and silica. It consists of two layers – the upper
layer and the lower mantle. The average temperature of
the upper mantle is 870°C and the rock here are in semi
solid state. The average temperature of the lower mantle
would be 2,200°C and it is in a solid state.
Continental Crust and Oceanic Crust

3. corE
• It extends from 2900 km to about 6400 km below the crust.

• Its radius is about 3500 km.
• This layer has very high temperature and pressure.
• It is the innermost layer of the earth.
• It is mainly made up of nickel and iron. Therefore, it is also known as NIFE. Here, NI
stand for Nickel and FE stands for ferrous (Iron).

• It consists of about 83% of the volume of the earth.
• The density of core varies from 9.9 to 13 gm/cm3.

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