The Origin Of Earth’s Mantle Nitrogen: Primordial Or Early Biogeochemical Cycling?
Earth’s Mantle Nitrogen Content Is Comparable To That Found In Its Nitrogen-Rich Atmosphere.
Mantle Nitrogen has been proposed to be primordial or sourced by later subduction, yet its origin has not been elucidated. Here we model N partitioning during the magma ocean stage following planet formation and the subsequent cycling between the surface and mantle over Earth history using argon (Ar) and N isotopes as tracers.
The partitioning model, constrained by Ar, shows that only about 10% of the total N content can be trapped in the solidified mantle due to N’s low solubility in magma and low partitioning coefficients in minerals in oxidized conditions supported from geophysical and geochemical studies.
A possible solution for the primordial origin is that Earth had about 10 times more N at the time of magma ocean solidification. We show that the excess N could be removed by impact erosion during late accretion. The cycling model, constrained by N isotopes, shows that mantle N can originate from efficient N subduction, if the sedimentary N burial rate on early Earth is comparable to that of modern Earth.
Such a high N burial rate requires biotic processing. Finally, our model provides a methodology to distinguish the two possible origins with future analysis of the surface and mantle N isotope record.
H. Kurokawa, M. Laneuville, Y. Li, N. Zhang, Y. Fujii, H. Sakuraba, C. Houser, H. J. Cleaves II
Comments: 43 pages, 14 figures, accepted for publication in Geochemistry, Geophysics, Geosystems
Subjects: Geophysics (physics.geo-ph); Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2204.14002 [physics.geo-ph] (or arXiv:2204.14002v1 [physics.geo-ph] for this version)
https://doi.org/10.48550/arXiv.2204.14002
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Related DOI:
https://doi.org/10.1029/2021GC010295
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Submission history
From: Hiroyuki Kurokawa
[v1] Thu, 21 Apr 2022 02:38:37 UTC (14,022 KB)
https://arxiv.org/abs/2204.14002
Astrobiology
