The Oxygen Valve on Hydrogen Escape Since the Great Oxidation Event

The Great Oxidation Event (GOE) was a 200 Myr transition circa 2.4 billion years ago that converted the Earth’s anoxic atmosphere to one where molecular oxygen (O₂) was abundant (volume mixing ratio >10⁻⁴).

This significant rise in O₂ is thought to have substantially throttled hydrogen (H) escape and the associated water (H₂O) loss. Atmospheric estimations from the GOE onward place O₂ concentrations ranging between 0.1% to 150% PAL, where PAL is the present atmospheric level of 21% by volume.

In this study we use WACCM6, a three-dimensional Earth System Model to simulate Earth’s atmosphere and predict the diffusion-limited escape rate of hydrogen due to varying O₂ post-GOE.

We find that O₂ indirectly acts as a control valve on the amount of hydrogen atoms reaching the homopause in the simulations: less O₂ leads to decreased O₃ densities, reducing local tropical tropopause temperatures by up to 18 K, which increases H₂O freeze-drying and thus reduces the primary source of hydrogen in the considered scenarios. The maximum differences between all simulations in the total H mixing ratio at the homopause and the associated diffusion-limited escape rates are a factor of 3.2 and 4.7, respectively. The prescribed CH₄ mixing ratio (0.8 ppmv) sets a minimum diffusion escape rate of ≈2×10¹⁰ mol H yr⁻¹, effectively a negligible rate when compared to pre-GOE estimates (∼10¹²−10¹³ mol H y⁻¹).

Because the changes in our predicted escape rates are comparatively minor, our numerical predictions support geological evidence that the majority of Earth’s hydrogen escape occurred prior to the GOE. Our work demonstrates that estimations of how the hydrogen escape rate evolved through Earth’s history requires 3D chemistry-climate models which include a global treatment of water vapour microphysics.

Gregory J. Cooke, Dan R. Marsh, Catherine Walsh, Felix Sainsbury-Martinez, Marrick Braam

Comments: 32 pages, 7 figures, 1 table. Revised after first review in Climate of the Past this https URL
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Geophysics (physics.geo-ph)
Cite as: arXiv:2512.09844 [astro-ph.EP] (or arXiv:2512.09844v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2512.09844
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Submission history
From: Gregory Cooke
[v1] Wed, 10 Dec 2025 17:23:09 UTC (3,119 KB)
https://arxiv.org/abs/2512.09844

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