The occurrence of nitrate on the early earth and its role in the evolution of the prokaryotes

It has been suggested that the evolution of the respiratory system coupled to oxidative phosphorylation occurred under anaerobic conditions in which inorganic compounds, principally nitrate, served as electron acceptors. Such a hypothesis requires that nitrate be produced, consistently and at adequate concentrations for utilization in biological processes, at a time when much of the Earth's surface was still in a relatively reduced state. This paper is directed towards a consideration of the possible sources of nitrate under primeval conditions, its stability, and its concentration in sites favorable to the evolution of the bacteria.