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SUMMARY:The Oxygen Valve on Hydrogen Escape Since the Great Oxidation Even
 t - Greg Cooke / IoA
DTSTART:20250507T121500Z
DTEND:20250507T124000Z
UID:TALK231727@talks.cam.ac.uk
CONTACT:128254
DESCRIPTION: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 h
 ave 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 esc
 ape 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 indirec
 tly acts as a control valve on the amount of hydrogen atoms reaching the h
 omopause in the simulations: less  O2 leads to decreased O3 densities\, re
 ducing local temperatures by up to 5 K\, which increases H2O freeze-drying
 . For the considered scenarios\, the maximum difference in the total H mix
 ing ratio at the homopause and calculated diffusion-limited escape rates i
 s 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. 
LOCATION:The Hoyle Lecture Theatre + Zoom 
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