- The planet earth initially was a barren, rocky and hot object with a thin atmosphere of hydrogen and helium. This is far from the present day picture of the earth.
- Hence, there must have been some events– processes, which may have caused this change from rocky, barren and hot earth to a beautiful planet with ample amount of water and conducive atmosphere favouring the existence of life.
- The earth has a layered structure.
- From the outermost end of the atmosphere to the centre of the earth, the material that exists is not uniform.
- The atmospheric matter has the least density.
- From the surface to deeper depths, the earth’s interior has different zones and each of these contains materials with different characteristics.
Formation of the layered structure in the lithosphere:
- The earth was mostly in a volatile state during its primordial stage.
- Due to the gradual increase in density the temperature inside has increased. As a result of the material inside started getting separated depending on their densities.
This process is called differentiation. - This allowed heavier materials (like iron) to sink towards the centre of the earth and the lighter ones to move towards the surface.
- Due to this earth got divided into layers like the crust (outermost), mantle, outer core and inner core (innermost).
- From the crust to the core, the density of the material increases.
Eolution of Atmosphere and Hydrosphere:
- The early atmosphere, with hydrogen and helium, is supposed to have been stripped off as a result of the solar winds.
- Then, during the cooling of the earth, gases and water vapour were released from the interior solid earth. This started the evolution of the present atmosphere. This process is called degassing.
- Continuous volcanic eruptions contributed water vapour and gases to the atmosphere.
- As the earth cooled, the water vapour released started getting condensed.
- The carbon dioxide in the atmosphere got dissolved in rainwater and the temperature further decreased causing more condensation and more rains.
- The rainwater falling onto the surface got collected in the depressions to give rise to oceans.
The Evolution of the Earth,The Evolution of the Earth
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