Interior of the Earth

Interior Of The Earth: An understanding of the earth's interior is essential to understand the nature of changes going on over the earth's surface, which are related to the deep-laid internal forces operating from within the earth.

Evidences about the Earth Interior: Exploring earth beneath our feet is a very difficult task, t is, in fact, more difficult than studying the Spaces The deepest mine in the world in South Africa is only about 4 km deep. Only upper part of the earth's crust just below its surface could be known more or less by direct observations. The lower part  is beyond the reach of direct observation and our knowledge about it is based upon indirect scientific evidences, These indirect sources are temperature and pressure inside the earth, density of its different shells, behaviour of earthquake waves and evidence from meteorites.By using seismograph, a graphic recording of the earthquake waves or vibrations is made, and scientists are able to get some idea of the kind of rocks which are found below the earth's surface.

A Sectional Profile of Earth's Structure:  The structure of the earth's interior is layered, and broadly three layers can be identified- crust, mantle and the core.

Crust is the outermost layer with an average thickness of about 100 km. It forms 0.5 per cent of the earth's volume. Below its outer covering which comprises sedimentary material, their lies the crystalline,igneous and metamorphic rocks, which are acidic in nature.

Mantle is the second layer, which lies below the crust. It forms 80% of the earth's volume. It is also known as a solid rocky layer. Peridotite is the most important rock forming  mineral here. The trend of increase fn temperature with depth, which is noticed in the crust does not continue downward in the mantle. This shows that the mantle can transmit heat through some form of convection. The Mantle exhibits a plastic behaviour, which means that the material behaves like an elastic solid when it is subjected to short lived stress, such as seismic waves. However, under long-term stresses, the same rocky material will flow and this allows the S waves to penetrate through the mantle. But as this layer is not capable of storing elastic energy, it is thus incapable of generating the earthquakes..

Core lies between 2900 km to 6400 km below the earth's surface and accounts for 1/6 of the earth's volume. The central core has the heaviest mineral of highest density. It is composed of nickel and iron (ferrous).

Core comprises 1/3rd of the total mass of the earth and 1/6 of its volume, The pressure in this layer B million of times that of atmospheric pressure at the surface and the average temperature here is 4000 C-5000° C. It is divided into:

Inner Core: It is solid in nature. Iron and Nickel are main minerals here,

Outer Core: It is in liquid form. Here the pressure is comparatively lesser and this allows the hot iron to melt. This molten iron gradually flows to the outer core and helps in maintaining earth's magnetism.

Earth's rotation and unequal distribution of heat in the earth's interiors contributes to this solid nature of inner core despite the higher temperature in this layer, It is believed that initially the earth would have been in liguid state where vigorous mixing of liquid iron happened. But gradually, the material of the core started segregating. With the cooling of the core, some iron particles started migrating downward, and further pushed the lighter material towards the outer edge of the core. The sinking iron rich Earth's rotation and unequal distribution of heat in the earth's interiors contributes to this solid nature of  components, depleted of the lighter elements which act to depress the melting point, began to solidify