Question

select the correct answer.
how did cyanobacteria affect earths 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.

Explanation:

Cyanobacteria are photosynthetic organisms. Through photosynthesis, they take in carbon dioxide (\(CO_2\)) and release oxygen (\(O_2\)). This process gradually changed the composition of Earth's early atmosphere. Ultraviolet rays are not eliminated by cyanobacteria (ozone layer formed later from oxygen helps with UV, but cyanobacteria don't directly eliminate UV). They don't replace oxygen with carbon dioxide (it's the opposite - produce oxygen). And they don't absorb ozone (ozone is \(O_3\), cyanobacteria produce \(O_2\)).

Answer:

C. They replaced carbon dioxide with oxygen in the atmosphere.