Question

The first life forms on earth were heterotrophs and the atmosphere was reducing. The advent of first autotrophs also, however, did not immediately make the atmosphere oxidizing. The most probable reason for this was

• A. The oxygen produced was immediately consumed by the autotrophs themselves.
• B. The oxygen produced immediately escaped into environment to help in formation of ozone layer.
• C. The oxygen produced immediately escaped to outer space due to lack of ozone to trap it.
• D. The first autotrophs never released oxygen as they used sources other than water for photosynthesis.

Answer 1

Answer: (D)

The first autotrophs never released oxygen as they used sources other than water for photosynthesis.

The first life forms to be appeared on earth were much like coacervates. They were anaerobic heterotrophs as at that time the atmosphere of earth was reducing and they couldn't prepare their own food. With time, autotrophs appeared. But the first autotroph never released oxygen because they used sources other than water for photosynthesis (for example, some bacteria used amino acids) and as a result atmosphere didn't become oxidised.

So, the correct answer is 'The first autotrophs never released oxygen as they used sources other than water for photosynthesis'.