Question

In the ancient atmosphere free nitrogen, oxygen and carbon dioxide were not present because
A. Of a large amount of hydrogen and high temperatures.
B. Carbon would have combined with hydrogen to methane.
C. Any free oxygen would have combined with iron, silicon, aluminium etc to form minerals of the earth crust.
D. All of the above.

Answer 1

Hint: Early earth environment is not suitable to support life. Ancient earth has a reducing atmosphere, primitive environment so much hostile, due to the presence of high temperature, absence of oxygen, no ozone layer is present to prevent the earth from harmful radiations. Radiation absorption species like carbon dioxide and methane raise the earth temperature.

Complete answer:
Early earth atmosphere is reducing in nature, oxygen is not present in free form instead it is present in compound form due to reducing environment, it form oxide such as iron oxide, silicon oxide, an abundant amount of hydrogen is in a combined form with oxygen, nitrogen and carbon, that form water, methane, ammonia and cyanide like compound.

The first life form is anaerobic in nature, which can survive without consuming oxygen molecule because there no such free oxygen if present, slowly anaerobic life evolve and give rise to aerobic life form, which releases free oxygen in the atmosphere and make a suitable environment for evolved life form and create a diversity of life forms. The known organism which is fossilized gives evidence of the simplest life form and aerobic respiration by cyanobacteria.

That microorganism possesses some green colour pigment which performs photosynthesis, in which carbon dioxide is mixed with water, which is present in abundant amounts during the early period of earth, and produce free oxygen species in the atmosphere, that stabilize the earth atmosphere and make life possible on earth.

Hence, the correct answer is option (D).

Note: It is a hypothetical assumption, which states that life originates from protobionts, which is the precursor cell for the true living cells, such protobionts arise from the mixture of different kind compounds present at the early stage of earth atmosphere, which is reducing in nature.