Where does most of the nitrogen in earths atmosphere come from?

A: fires

B: erosion

C: bacteria

D: the breakdown of carbon dioxide

C: bacteria.

Explanation:

This is the only answer that make sense, because nitrogen fixation is carried out by bacterias, algae and human activity. When organisms use it and release it, nitrogen is suffer a breakdown process, traveling as a gas to the atmosphere.

Most of the nitrogen in earths atmosphere comes from bacteria.