Nitrogen fixation is a process by which molecular nitrogen in the air is converted into ammonia or related nitrogenous compounds in soil. Atmospheric nitrogen is molecular dinitrogen, a relatively nonreactive molecule that is metabolically useless to all but a few microorganisms.
This solar energy conversion process is known as photosynthesis. ... At this time, the oxygen level was approximately 10% of its present atmospheric concentration. ... The presence of ozone enabled organisms to develop and live on the land.
