Published May 2024
| Published
Journal Article
Open
New Estimates of Nitrogen Fixation on Early Earth
Abstract
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. A previous study estimated nitrogen fixation in the Hadean Earth’s N2/CO2-dominated atmosphere; however, that previous 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 Hadean Earth. We use the Chemical Equilibrium with Applications (CEA) thermochemical model to estimate lightning-induced NO and HCN formation and an updated version of 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. Our updated 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 generating HCN via HCN2, inspired by the experimental results which suggest that reactions with CH radicals (from CH4 photolysis) may facilitate the incorporation of N into the molecular structure of aerosols. When the HCN2 reactions are added, we find that the HCN rainout rate rises by a factor of five in our 1-bar case and is about the same in our 2- and 12-bar cases. Finally, we estimate the equilibrium concentration of fixed nitrogen species under a kinetic steady state in the Hadean ocean, considering loss by hydrothermal vent circulation, photoreduction, and hydrolysis. These results inform our understanding of environments that may have been relevant to the formation of life on Earth, as well as processes that could lead to the emergence of life elsewhere in the universe.
Copyright and License
© 2024 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).
Acknowledgement
We thank our three anonymous peer reviewers for constructive comments on our paper.
Funding
This research was supported in part by Caltech GPS Discovery Grant P2639826. This research was supported in part by a JPL RTD grant, “ASSESSING ORIGIN OF LIFE (OOL) SCENARIOS FOR EXOPLANET STUDIES.” M.L.W. and D.A. are funded by NASA through the NASA Hubble Fellowship awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS5-26555.
Contributions
Conceptualization, D.A. and M.L.W.; Methodology, M.C., D.A. and M.L.W.; Software, M.C., D.A., M.L.W., P.D. and Y.L.Y.; Validation, D.A. and M.L.W.; Formal analysis, M.C., D.A., M.L.W. and P.D.; Investigation, M.C.; Data curation, M.C. and P.D.; Writing—original draft, M.C.; Writing—review & editing, M.C., D.A., M.L.W., P.D. and Y.L.Y.; Visualization, M.C.; Supervision, D.A. and M.L.W.; Project administration, Y.L.Y. All authors have read and agreed to the published version of the manuscript.
Data Availability
This study was a theoretical study and the models we used are appropriately referenced.
Conflict of Interest
The authors declare no conflict of interest.
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Additional details
- PMCID
- PMC11122333
- California Institute of Technology
- Division of Geological and Planetary Sciences P2639826
- Jet Propulsion Laboratory
- National Aeronautics and Space Administration
- NASA Hubble Fellowship
- National Aeronautics and Space Administration
- NAS5-26555
- Caltech groups
- Division of Geological and Planetary Sciences