A Late-Hadean Window for Life’s Origin Defined by Co-Evolving Nitrogen and Carbon Cycles

The origin of life required ample bioavailable nitrogen, yet its abundance and cycling on the prebiotic Earth remain uncertain. We couple a global abiotic nitrogen cycle to a self-consistent model of carbon cycling and ocean chemistry to estimate nitrogen speciation in evolving Hadean surface environments. This whole-Earth-system framework reveals a previously unrecognized planetary transition: as atmospheric CO₂ declined, lightning-driven production of oxidized nitrogen weakened, while oceanic sinks intensified under high dissolved Fe²⁺ and rapid continental and sediment growth enhanced ammonia burial. These coupled processes maintained abundant reduced nitrogen but drove oxidized species below prebiotic thresholds after ~4.1 Ga, constraining the plausible timing of life’s origin to the late Hadean—consistent with geochemical and phylogenetic constraints on Earth’s earliest life. When combined with trends in surface temperature, ocean pH, and late accretion, our results delineate a chemically and physically optimal interval when both nitrogen availability and planetary conditions favored prebiotic chemistry, establishing a quantitative framework for assessing life’s emergence on Earth and other worlds.