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write a short note on the interior structure of the earth

Just like an onion, the earth is made up of several concentric layers with one inside another.The structure of earth's interior has broadly three layers-crust,mantle and core.
Crust
1.It is a uppermost layer over the earth’s surface.
2.It is the thinnest of all the layers.
3.It is about 35 km thick on the continental masses and only 5 km thick on the oceans.
4.The continental mass mainly constituents of silica and alumina minerals. It is thus called sial whereas oceanic crust mainly consist of silica and magnesium.It is therefore called sima.
Mantle
1.Just beneath the crust lies the mantle.
2.It extends up to a depth of 2900 km. below the crust.
3.It also consist of silica and magnesium.
Core
1.The innermost layer of the earth is called the core.
2.It has a radius of about 3500 km.
3.It is mainly made up of nickel and iron and therefore it is called nife.
4.Due to very high temperature and pressure, it exist in solid state.

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The interior of Earth is not subject to direct investigation, but its properties must be indirectly deduced from the study of earthquake waves that propagate through the interior rocks. From an earthquake near the surface, both pressure (compression) waves and transverse (side‐to‐side) waves move outwards in all directions. Wave energy moving into the interior, however, has its path slowly changed by refraction as the wave moves through regions of slowly changing properties. These waves reach the surface after a time that depends on the length of the path and the velocity of propagation at each point along that path. Careful analysis at seismographic stations of the time of arrival of earthquake waves over the surface of Earth yields information about the densities, temperatures, and pressures of Earth's interior. A thin crust (at its thickest only 30 kilometers deep), which contains the continental masses and the ocean floors, overlies a denser outermantle.The uppermost layer of the mantle acts as solid material, alithosphereno more than about 80 kilometers deep. Most of the mantle slowly flows under pressure and acts as a plastic, or malleable,asthenosphere.

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