How did cyanobacteria affect earth's early atmosphere?
a.
they replaced oxygen with carbon dioxide in the atmosphere.
b.
they eliminated the harmful ultraviolet rays of the sun.
c.
they replaced carbon dioxide with oxygen in the atmosphere.
d.
they absorbed ozone molecules from the atmosphere.

The correct answer is option - C. They replaced carbon dioxide with oxygen in the atmosphere.

Explanation:

Cyanobacteria or Blue-green algae is a group of bacteria that is making its own food using water and carbon dioxide in the presence of sunlight, the process of photosynthesis

These organisms release oxygen as a byproduct of photosynthesis in the atmosphere. Through this process, these organisms replaced carbon dioxide with oxygen in the atmosphere in the early earth.

Thus, the correct answer is option C. They replaced carbon dioxide with oxygen in the atmosphere.

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hope that !         : )