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New Estimates of Nitrogen Fixation on the Hadean Earth

Presentation #209.01 in the session “Astrobiology and Origins of Life”.

Published onOct 26, 2020
New Estimates of Nitrogen Fixation on the Hadean Earth

Fixed nitrogen species generated by the early Earth’s atmosphere are thought to be critical to the emergence of life and the sustenance of early metabolisms. Previously, Wong et al. (2017) estimated nitrogen fixation in the Hadean Earth’s N2/CO2-dominated atmosphere, but that study only considered a limited chemical network that produces NOx species (i.e., no HCN formation) via the thermochemical dissociation of N2 and CO2 in lightning flashes, followed by photochemistry. Here, we present an updated model of nitrogen fixation on the Hadean Earth. We use CEA (Chemical Equilibrium with Applications) to estimate lightning-induced NO and HCN formation and KINETICS, the 1-D Caltech/JPL photochemical model, to assess the photochemical production of fixed nitrogen species that rain out into the Earth’s early ocean. Finally, we estimate the equilibrium concentration of fixed nitrogen species under kinetic steady state in the Hadean ocean, considering loss by hydrothermal vent circulation and photoreduction. Our updated model photochemical model contains hydrocarbon and nitrile chemistry and we use a Geant4 simulation platform to consider nitrogen fixation stimulated by solar energetic particle deposition throughout the atmosphere. We study the impact of a novel reaction pathway for generated HCN via HCN2, inspired by the experimental results of Trainer et al. (2012), which suggest that reactions with CH radicals (from CH4 photolysis) may facilitate the incorporation of N into the molecular structure of aerosols. Preliminary results show that this new reaction pathway results in a four-fold increase in the total HCN rainout rate.

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