(World Geography) - Interior of The Earth, The Lithosphere and Asthenosphere


Concepts of Geography, Natural Resources


One of the earliest structuring of the earth’s interior was suggested by Edward Suess who considered the interior to be differentiated into SIAL, SIMA and NIFE. SIAL is composed of granite and dominated by Silica and Aluminum. It floats over SIMA which is denser and has Silica and Magnesium as main constituents.

However this is now replaced by more sophisticated detailed structuring Based on seismic studies, the earth’s interior has been divided into three layers- crust, mantle and core.

Mohorovicic Discontinuity

The Crust: It is the outermost solid part of the earth. It is brittle in nature. The thickness of the crust varies under the oceanic and continental areas. Oceanic crust is thinner as compared to the continental crust. The continental crust is thicker in the areas of major mountain systems . It is as much as 70 Km thick in the Himalayan region.

The Mantle

The Mantle: The portion of the interior below the crust is called the mantle. The dividing line which separates the crust above from the mantle below is called as Mohorovicic or Moho discontinuity. The crust and the uppermost part of the mantle are called lithosphere. Its thickness ranges from 10-200 Km. The upper portion of the mantle is called asthenosphere. It is the main source of magma that find its way to the surface during volcanic eruptions.

The Core: The outer core is in liquid state while the inner core is in solid state. The core is made up of very heavy material mostly constituted by nickel and iron. It is sometimes referred to as the nife layer. The core-mantle boundaries is located at the depth of 2,900 Km.


The lithosphere is the solid, brittle outermost layer of the Earth. It includes the crust and the cooler, brittle upper part of the mantle.

Some tens of kilometers deep in the Earth, the brittle lithospheric rocks gives way gradually to a plastic, or “soft, “ layer named the asthenosphere. But at still greater depth in the mantle, the strength of the rocks material increases again. You can think of the lithosphere on top of the asthenosphere as a hard, brittle shell resting on a soft, plastic underlayer.

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