Summary

Nitrogen is the major component of Earth's atmosphere and plays important roles in biochemistry. Biological systems have evolved a variety of mechanisms for fixing and recycling environmental nitrogen sources, which links them tightly with terrestrial nitrogen reservoirs. However, prior to the emergence of biology, all nitrogen cycling was abiological and this cycling may have set the stage for the origin of life.

To study this, a microbiologist, a planetary scientist and a geochemist came together to build a global systems model to understand how nitrogen cycling would proceed on terrestrial planets with comparable geodynamic activity to the Earth, but on which life does not arise. We constructed a kinetic mass-flux model of nitrogen cycling in its various major chemical forms (e.g., N₂, reduced (NHx) and oxidized (NOx) species) between major planetary reservoirs (the atmosphere, oceans, crust and mantle), and including inputs from space. The total amount of nitrogen species which can
be accommodated in each reservoir and the ways fluxes and reservoir sizes may have changed over time in the absence of biology were explored. Given a partition of volcanism between arc and hotspot types similar to the modern ones, our global nitrogen cycling model predicts a signifcant increase in oceanic nitrogen content over time, mostly as NHx, while atmospheric N₂ content could be lower than today. The transport timescales between reservoirs are fast compared to the evolution of the environment, thus atmospheric composition is tightly linked to surface and interior processes.
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ELSI Researchers｜Cleaves, H. James