So, the correct answer is option A.
- Life began on earth some 3.8 million years ago and was initially occupied by the single-celled prokaryotic cells, such as bacteria. Multicellular organisms evolved over a billion years later.
- However, studies conducted on the genetic material suggest that single-celled living organisms that used carbon dioxide as a source of carbon and oxidized inorganic materials to extract energy were the first forms of life on earth.
- These organisms are called chemoautotrophs.
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