Question

What gas was present in earth's earliest atmosphere and used by cyanobacteria during photosynthesis?

A.
carbon dioxide

B.
nitrogen

C.
oxygen

D.
methane

Answer 1

C. Oxygen

These microbes conduct photosynthesis: using sunshine, water and carbon dioxide to produce carbohydrates and, yes, oxygen. In fact, all the plants on Earth incorporate symbiotic cyanobacteria (known as chloroplasts) to do their photosynthesis for them down to this day

Answer 2

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