A revised lower estimate of ozone columns during Earth's oxygenated history

Gregory Cooke; Dan Marsh; Catherine Walsh; Benjamin Black; Jean-François Lamarque

doi:10.1098/rsos.211165

paper

A revised lower estimate of ozone columns during Earth's oxygenated history

arXiv:2102.11675 · doi:10.1098/rsos.211165

Abstract

The history of molecular oxygen (O $_{2}$ ) in Earth's atmosphere is still debated; however, geological evidence supports at least two major episodes where O $_{2}$ increased by an order of magnitude or more: the Great Oxidation Event (GOE) and the Neoproterozoic Oxidation Event. O $_{2}$ concentrations have likely fluctuated (between $1 0^{- 3}$ and $1.5$ times the present atmospheric level) since the GOE $\sim 2.4$ Gyr ago, resulting in a time-varying ozone (O $_{3}$ ) layer. Using a three-dimensional chemistry-climate model, we simulate changes in O $_{3}$ in Earth's atmosphere since the GOE and consider the implications for surface habitability, and glaciation during the Mesoproterozoic. We find lower O $_{3}$ columns (reduced by up to $4.68$ times for a given O $_{2}$ level) compared to previous work; hence, higher fluxes of biologically harmful UV radiation would have reached the surface. Reduced O $_{3}$ leads to enhanced tropospheric production of the hydroxyl radical (OH) which then substantially reduces the lifetime of methane (CH $_{4}$ ). We show that a CH $_{4}$ supported greenhouse effect during the Mesoproterozoic is highly unlikely. The reduced O $_{3}$ columns we simulate have important implications for astrobiological and terrestrial habitability, demonstrating the relevance of three-dimensional chemistry-climate simulations when assessing paleoclimates and the habitability of faraway worlds.

Published in Royal Society Open Science. 20 pages, 8 figures

A revised lower estimate of ozone columns during Earth's oxygenated history

Abstract

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