Abstract

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. This rise in O2 is thought to have substantially throttled hydrogen (H) escape and the associated water (H2O) loss. 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 concentrations based on atmospheric estimations from the GOE onward, ranging between 0.1 PAL to 150 PAL , where PAL is the present atmospheric level of 21 % by volume. 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 temperatures by up to 5 K, which increases H2O freeze-drying. For the considered scenarios, the maximum difference in the total H mixing ratio at the homopause and calculated diffusion-limited escape rates is a factor of 3.2 and 4.7, respectively, with the prescribed CH4 mixing ratio setting a minimum diffusion escape rate of ≈ 2 × 10^10 mol H/yr. These numerical predictions support geological evidence that the majority of Earth’s hydrogen escape occurred prior to the GOE .