Temperature, Pressure and Density of Earth’s Interior


Temperature

Rise in temperature with increase in depth is observed in mines and deep wells. These evidences along with molten lava erupted from the earth’s interior, support that temperature increases towards the centre of the earth.

The different observations show that the rate of increase of temperature is not uniform from the surface towards the earth’s centre. It is faster at some places than at others.

In the beginning this increase is at an average rate of 1°C for every 32 metres increase in depth. At such a constant rate of increase in temperature, at 10 km depth, the temperature will be approximately 300°C and at 40 km depth it will be 1200°C. At this rate, earth’s interior should be in a molten state. Yet it is not so because the rocks buried under the pressure of several km thickness of overlying rocks melt at higher temperature than similar rocks at the surface.

A basaltic lava rock which melts at 1250°C at the surface will melt at 1400°C at 32 km depth. The extra heat required for melting is produced by radioactivity. It is the result of breakdown of atomic nuclei of minerals emitting radiant energy in the form of heat from the rocks.

The behaviour of earthquake waves is another evidence for this phenomenon. They further confirm that the composition of different layers is as variable as is the rate of change of temperature. While in the upper 100 km, the increase in temperature is at the rate of 12°C per km, in the next 300 km it is 20°C per km but is only 10°C per km below it. Thus the rate of increase of temperature beneath the surface decreases towards the centre.

The temperature at the centre is estimated to lie somewhere between 3000°C and 5000°C.Such a high temperature inside the earth may be due to chemical reactions under high pressure conditions and disintegration of radio active elements.

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Pressure

The pressure also increases from the surface towards the centre of the earth due to huge weight of the overlying rocks. Therefore in deeper portions, the pressure is tremendously high. The pressure near the centre is considered to be 3 to 4 million times the pressure of atmosphere at sea level. At high temperature, the material beneath will melt towards the central part of the earth. This molten material under tremendous pressure conditions acquires the property of a solid and is probably in a plastic state.

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Density

Due to increase in pressure and presence of heavier materials towards the earth’s centers, the density of earth’s layers also goes on increasing. Obviously the materials of the innermost part of the earth are very dense as already stated.

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Bibliography : NIOS – Geography

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