Summary of "Earth Without Life: A Systems Model of a Global Abiotic Nitrogen Cycle," by Matthieu Laneuville, Masafumi Kameya and H. James Cleaves II in *Astrobiology* (2018)

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