The primeval atmosphere probably contained an abundance of fixed nitrogen in the form of NH3. But as the atmosphere became more oxidising, NH3 was replaced by N2, and the supply of fixed nitrogen was limited to nitrates, etc., produced by the action of lightning; and the need arose to develop enzymes capable of ‘fixing’ N2 itself. Micro-organisms, mainly those living symbiotically in the root nodules of legumes, now fix about 108 tons of nitrogen per year73; just about half this amount was fixed by industrial processes in 197157.
KeywordsNitrogen Fixation Mossbauer Spectrum Irreversible Evolution Sulphite Oxidase Reductive Fixation
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