Nitrogen Oxides in Early Earth's Atmosphere as Electron Acceptors for Life's Emergence.

We quantify the amount of nitrogen oxides (NOx) produced through lightning and photochemical processes in the Hadean atmosphere to be available in the Hadean ocean for the emergence of life. Atmospherically generated nitrate (NO) and nitrite (NO) are the most attractive high-potential electron acceptors for pulling and enabling crucial redox reactions of autotrophic metabolic pathways at submarine alkaline hydrothermal vents. The Hadean atmosphere, dominated by CO and N, will produce nitric oxide (NO) when shocked by lightning.