Question

When earth originated, there was large amount of methane and other hydrocarbons but now in the present atmosphere it is replaced by

• A. Minerals
• B. $O_2$
• C. Coal dust
• D. $C{O}_2$, $H_2$

Answer 1

The correct option is D $C{O}_2$, $H_2$

The primitive atmosphere of earth was reducing atmosphere that lack molecular oxygen but was rich in water vapour, carbon monoxide, carbon dioxide, nitrogen and hydrogen. Absence of oxygen and various high energy sources (UV rays, high temperature and lightening) allowed chemical reaction hydrogen and carbon to produce methane and other hydrocarbons. In absence of oxygen and presence of high temperature methane was present in unspoiled gaseous form and facilitated further chemical reactions to produce more complex protein structures. With origin of photoautotrophs, the organisms that use light as source of energy and carbon dioxide as chief carbon source, earth’s atmosphere II was replaced with atmosphere III. These photoautotrophs use water as electron donor during photophosphorylation that results in production of oxygen thereby adding oxygen to otherwise primitive reducing atmosphere. This makes option B incorrect as photoautotrophs were the source of oxygen. Presence of molecular oxygen oxidized the reduced methane and other hydrocarbons into carbon dioxide which makes option D correct. Options A and C are incorrect as oxidation of methane and hydrocarbons produce carbon dioxide, not the coal dust and hydrogen gas.

Therefore, the correct answer is option D.