Structure of the Earth

Structure of the Earth: The interior structure of the Earth is layered in spherical shells, like an onion. These layers can be defined by their chemical and their rheological properties. Earth has an outer silicate solid crust, a highly viscous mantle, a liquid outer core that is much less viscous than the mantle, and a solid inner core. Scientific understanding of the internal structure of the Earth is based on observations of topography and bathymetry, observations of rock in outcrop, samples brought to the surface from greater depths by volcanoes or volcanic activity, analysis of the seismic waves that pass through the Earth, measurements of the gravitational and magnetic fields of the Earth.

This Topic is Part of Broad Physical features of World

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 mean thickness of oceanic crust is 5 km whereas that of the continental is around 30 km.

The Mantle

• The portion of the interior beyond the crust is called the mantle. The mantle extends from Moho’s discontinuity to a depth of 2,900 km.
• The mantle contains a weaker zone called asthenosphere.
• It is from this that the molten rock materials find their way to the surface.
• The material in the upper mantle portion is called magma.
• Once it starts moving towards the crust or it reaches the surface, it is referred to as lava.

The Core

• The coremantle boundary is located at the depth of 2,900 km. 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 is divided into two layers: Outer Core and Inner Core.
• Outer core is in liquid state. The liquid outer core surrounds the inner core and is believed to be composed of iron mixed with nickel and trace amounts of lighter elements.
• Inner core is in solid state. Inner Core was discovered in 1936 by Inge Lehmann and is generally believed to be composed primarily of iron and some nickel. It is not necessarily a solid, but, because it is able to deflect seismic waves, it must behave as a solid in some fashion.

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