Earth Layers

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Earth Layers

Earth layers

The velocity and the path followed by earthquake waves, temperature and pressure conditions inside the earth tells us of varying physical properties, density and composition prevailing there. The structure of earth's interior is therefore layered. Below the surface capped by sedimentary material, upper layer of the crust is mainly composed of crystalline igneous and metamorphic rocks, acid in nature. The lower layer of the crust has basaltic and ultra-basic rocks. The layer of heavier or inner silicates is not found beneath oceans. The oceans are mostly underlaid by dark coloured basalt followed down by a thick greenish and tremendously hot layer. The continents are composed of lighter silicates termed as 'Sial' or Silica + Aluminium. The oceans have heavier silicates named as 'Sinia' or Silica + Magnesium. The continents of lighter material are floating in a sea of heavier and denser material. The central core has the heaviest mineral materials of highest density. It is composed of what is termed as 'Nife' or Nickel + Iron. A zone of mixed heavy metals and silicates separates the core from the other layers.

The table above summarizes the names, density and approximate thickness of different layers of earth's interior in order to know its structure.

Based upon variations in temperature and pressure, changes in density and velocity of earthquake waves along boundaries of different layers, their chemical composition and physical properties, layered nature of earth's structure is confirmed. Broadly, there are three layers - the crust, the mantle and the core. While the crust forms only 0.5 per cent of the volume of the earth. 16 per cent consists of the mantle and 83 percent makes the core. Earth being a spherical body, it has its centre at 6,400 km, namely the mean radius of the earth.

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