Abstract NH 3 or NH 4 + is an essential component of the abiotic synthesis of organic compounds for the origin of life and an efficient greenhouse gas to address the faint young Sun paradox on the early Earth. Sustainable NH 3 or NH 4 + on the N 2 -dominated prebiotic Earth’s surface requires potent abiotic N 2 reduction (ANR) in hydrothermal systems, which has not been detected in the geological record despite numerous laboratory demonstrations. Here we report high concentrations and extreme 15 N depletions of NH 4 + in hydrothermal veins in oceanic crusts drilled from the South China Sea basin. Our data indicate that abundant 15 N-depleted NH 4 + was produced by ANR in deep fluid but progressively overprinted by 15 N-enriched biogenic NH 4 + toward the surface. Modeling suggests that ANR could supply up to 9.0 – 10.8×10 10 mol⋅year -1 NH 4 + to global oceans, which is minor to the large nitrogen inventory in modern oceans, but could quickly fertilize the oceans and supply NH 3 to the atmosphere in the prebiotic Earth.
Sun et al. (Fri,) studied this question.