World Geography Part 3 – Earth’s Interior


  1. The earth is the only known planet where life is possible
  2. Earth is spherical in shape, hot water and molten lava eject out from earth’s interior
  3. World’s deepest mining is limited only to the depth of less than 5 km as the temperature below earth is very high.
  4. The interior of the earth –
  5. Because of huge size and changing nature of its internal composition, its not possible to make direct observation.
  6. We have limited information of earth’s interior, through mining and drilling operation , its so hot that it can even melt any tool for drilling.


Structure –

  1. The innermost layer surrounding the earth surface is called core.
  2. Core is the densest layer of the earth with its density more than 11.0.
  3. It is composed mainly of iron and nickel thus known as Nife.
  4. Core consist of two sub layers, the inner one is solid (C2) and the outer one is semi liquid (C1)
  5. The layer surrounding the core is mantle, is composed of basic silicates.
  6. Major constituent of mantle are magnesium and silicon, hence it’s also known as Sima (Silica+Magnesium).
  7. Its density varies from 3.1 to 5.1 and surrounded by the outermost layer of the earth, known as lithosphere and its density varies from 2.75 to 2.90.
  8. Major constituent elements of lithosphere are silica (Si) and aluminium (Al), it is also known as Sial.
  9. The outermost part of lithosphere is known as crust.


The sources which provide knowledge about the interior of the earth may be classified into

  1. Artificial sources
  2. Natural sources
  3. Evidence from the theories of the origin of earth


Artificial sources to understand Interior of the earth

We can know about the interior of the earth with the help of following sources

  • Temperature
  • Pressure
  • Density


  1. It increases with the depth, as observed in the mines and deep wells
  2. The molten lava erupted from the earth’s interior also support this fact.
  3. It’s not uniform from the surface towards the earth’s centre, in beginning its increases at an average rate of 1 degree Celsius for every 32 meters increase in depth.
  4. With such a speed it will be 300 degree celcius at a depth of 10 km, and 1200 degree celcius at 40 km.
  5. But its interior is not in molten state, because rocks buried under the pressure of several km thicknesses of overlying rocks melt at higher temperature
  6. Than similar rock on the surface, a basaltic lava rock which will melt at 1250 degree celcius at surface, will take 1400 degree celcius at 32 km of depth.

So from where we get extra heat –

It is being produced by radioactivity, as the result of breakdown of atomic nuclei of minerals emitting radiant energy from in the form of heat from the rocks.

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