Question

It is believed that the first organisms which inhabited earth's surface were

• A. Autotrophs
• B. Chemoheterotrophs
• C. Heterotrophs
• D. Chemoautotrophs

Answer 1

The correct option is B Chemoheterotrophs

The primitive atmosphere of earth was reducing atmosphere with little or no oxygen but was rich in water vapour, carbon monoxide, carbon dioxide, nitrogen and hydrogen. Complex organic molecules were formed in oceans as facilitated by presence of high temperature and monomers. These organic molecules served as source of carbon and energy source for the first organism on the earth. The organisms that use organic/inorganic compounds as their carbon source are called as heterotrophs while those that can synthesize their two organic compounds are known as autotrophs. Since, the first life forms fed on available organic compounds, they were heterotrophs.

Therefore, the correct answer is option C.