Question

How many years ago and in which environment did life originate on the earth?
A. 3.5 million years and reducing environment
B. 3.5 billion years and reducing environment
C. 4.5 million years and reducing environment
D. 4.5 billion years and reducing environment

Answer 1

Hint: Origin of life or evolutionary biology is termed as Abiogenesis which is a natural process by which life has arisen from the non-living matter, like simple organic compounds. The life of earth is estimated by available fossil evidence which is found on the earth.

Complete answer:
The scientist has found that the simple unicellular organisms which resemble modern Cyanobacteria were present on the earth about 3600 million years ago. The evidence on the fossils of old rocks suggests that life must have originated on this earth about 3.5 billion years ago. The atmosphere of the earth was completely different in the initial years of origin of life as compared to today. The atmosphere of the earth was reducing in the past as compared to oxidizing today.
The primitive atmosphere of the earth had water vapours, nitrogen, carbon dioxide, hydrogen, methane and ammonia. In the early stages of life on earth there was no oxygen in the Free State in sufficient quantities as compared to today. The first form of life was prokaryotic chemo-heterotrophic anaerobic organisms. The initial era on earth in which life originated on the planet was called the Azoic era.

Hence, the correct option is B. 3.5 billion years and reducing the environment.

Note: There were harsh conditions on earth and early organisms sustained themselves in these harsh conditions and after the temperature of earth cooled down, it led to formation of atmosphere and oceans. After these conditions more complex organisms were created which we can see today.