Question

Why were the first organisms an aerobic?

Answer 1

The first organisms. Bacteria have been the very first organisms to live on Earth. They made their appearance 3 billion years ago in the waters of the first oceans. At first, there were only anaerobic heterotrophic bacteria (the primordial atmosphere was virtually oxygen-free).

Answer 2

The first organisms were unicellular. Obviously, because of the absence of organs and organ systems, they couldn't physically respire (aerobically). Hence they respired anaerobically (chemically in the absence of free molecular oxygen)

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