(a) Hydrogen, Oxygen, Sodium
(b) Carbon, Hydrogen, Nitrogen
(c) Oxygen, Calcium, Phosphorus
(d) Carbon, Hydrogen, Potassium
Answer: (b)
Option (b) is correct:
As per the OparinHaldane hypothesis, the atmosphere of the early Earth may have been chemically reducing in nature, composed primarily of methane (CH4), ammonia (NH3), water (H2O), hydrogen sulphide (H2S), carbon dioxide (CO2) or carbon monoxide (CO), with phosphate (PO43-), molecular oxygen (O2) and ozone (O3) either rare or absent. The present composition of the earth’s atmosphere is chiefly contributed by nitrogen and oxygen. There are three stages in the evolution of the present atmosphere.
O The first stage is marked by the loss of the primordial atmosphere.
O In the second stage, the hot interior of the earth contributed to the evolution of the atmosphere.
O Finally, the composition of the atmosphere was modified by the living world through the process of photosynthesis. The early atmosphere, with hydrogen and helium, is supposed to have been stripped off as a result of the solar winds. This happened not only in the case of the earth but also in all the terrestrial planets, which were supposed to have lost their primordial atmosphere through the impact of solar winds. 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. The early atmosphere largely contained water vapour, nitrogen, carbon dioxide, methane, ammonia and very little free oxygen. The process through which the gases were outpoured from the interior is called degassing. Continuous volcanic eruptions contribute to water vapour and gases.
