Interior of the Earth and its 3 Layers Upsc

Interior of the earth

The earth’s interior can only be understood by indirect methods, as no one has gone deep inside the earth, due to high temperature and pressure.

The surface of the earth is due to a number of processes that happen deep inside the earth. The surface of the earth is due to exogenic as well the endogenic forces that happen inside the earth.

The radius of the earth is 6370 km and nobody has ever reached the centre of the earth. The information which we have got today is all based on observation and analysis of materials.

the interior of the earth diagram
Inside the Earth diagram By Kelvinsong – Own work, CC BY-SA 3.0,

Inside the earth

The Interior of the earth consists of Crust, Mantle, and Core. The continental crust is made of Sial which is expanded as Silica and Al-alumina.

And Oceanic crust is made up of Sima which is expanded as Silicon and Magnesium.

The interior of the earth is extremely hot and reaches as high as 5000 degrees Celsius. This is probably because of two reasons. One is the heating when the earth is formed and the other is the heat from the decay of the radioactive elements.


The crust is the outermost part, and it is brittle. Its thickness varies from oceanic and continental areas. The crust in the oceanic region is thinner than the continental crust.

Its average thickness is 5km in the case of oceanic crust and its average thickness is 30 km in the case of continental crust.

The continental crust is thickest in mountainous regions. For example, the Continental crust is 70 km thick in the Himalayan region.


The mantle is present after the crust. It extends from Moho’s discontinuity to a depth of 2900 km. The Mantle consists of a number of layers.

The upper layer of the Mantle is called Asthenospher that is extending up to 400km. The word Astheno means Weak. The lava comes through the Asthenosphere.

The crust of the uppermost part of the mantle is called Lithosphere and its thickness is about 10-200 km. The lower mantle extends beyond the asthenosphere which is in a solid-state.


The Final layer of the Interior of the earth is the core. The core is located at the depth of 2900 km. The outermost core is in a liquid state and the innermost core is in a solid state.

The core is made of Nickel and Iron and due to it is also referred to as Nife Layer.

Cause of the interior of the earth to separate into layers

The earth is divided into layers because of gravity and density. The stratification of Earth into layers was the reason for the formation of the Earth’s iron core.

This Iron core is possibly formed by radioactive decay and strong gravitation. This might have caused high temperatures and made iron melt.

As the molten iron moved to the center of the Earth due to gravity and it displaced the materials that are less dense to the surface.

Study of Interior of Earth

Scientists study the interior of the earth by studying seismic waves. These are recorded by an instrument called Seismograph. As it is impossible to drill the center of the earth, scientists use indirect observation of the underlying matters below the surface.

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* * All the Notes in this blog, are referred from Tamil Nadu State Board Books and Samacheer Kalvi Books. Kindly check with the original Tamil Nadu state board books and Ncert Books.
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