Nitrogen as it exists in our atmosphere - N2 - is too stable to be usable by most life forms, except a few bacteria. Other life forms require nitrogen in other forms - as ammonia, NH4+, nitrates or amines. The process by which N2 is converted to ammonia is called fixation.
Nitrogen is present in all amino acids, which are called that because they are both amines and organic acids. Life as we know it would be impossible without nitrogen, because there would be no amino acids and therefore no proteins.
Follow this link for an extensive treaty on the nitrogen cycle and how it is important to life on Earth.
Re: OT: Carbon Dioxide races -> known vs unknown -> terraforming mars -> is or is not
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