Biological regulation of atmospheric chemistry en route to planetary oxygenation

Abstract

Emerging evidence suggests that atmospheric oxygen may have varied before rising irreversibly ∼2.4 billion years ago, during the Great Oxidation Event (GOE). Significantly, however, pre-GOE atmospheric aberrations toward more reducing conditions-featuring a methane-derived organic-haze-have recently been suggested, yet their occurrence, causes, and significance remain underexplored. To examine the role of haze formation in Earth's history, we targeted an episode of inferred haze development. Our redox-controlled (Fespeciation) carbon-and sulfur-isotope record reveals sustained systematic stratigraphic covariance, precluding nonatmospheric explanations. Photochemical models corroborate this inference, showing Δ 36 S/Δ 33 S ratios are sensitive to the presence of haze. Exploiting existing age constraints, we estimate that organic haze developed rapidly, stabilizing within ∼0.3 ± 0.1 million years (Myr), and persisted for upward of ∼1.4 ± 0.4 Myr. Given these temporal constraints, and the elevated atmospheric CO 2 concentrations in the Archean, the sustained methane fluxes necessary for haze formation can only be reconciled with a biological source. Correlative δ 13 C Org and total organic carbon measurements support the interpretation that atmospheric haze was a transient response of the biosphere to increased nutrient availability, with methane fluxes controlled by the relative availability of organic carbon and sulfate. Elevated atmospheric methane concentrations during haze episodes would have expedited planetary hydrogen loss, with a single episode of haze development providing up to 2.6-18 × 10 18 moles of O 2 equivalents to the Earth system. Our findings suggest the Neoarchean likely represented a unique state of the Earth system where haze development played a pivotal role in planetary oxidation, hastening the contingent biological innovations that followed.sulfur mass-independent fractionation | organic haze | planetary oxidation | hydrogen loss | Neoarchean

The effects of metamorphism on iron mineralogy and the iron speciation redox proxy

“…Canfield et al, 2008;Clarkson et al, 2016;Geboy et al, 2013;Izon et al, 2017;Johnston et al, 2013;Johnston et al, 2010;Li et al, 2015;Planavsky et al, 2011;Sperling et al, 2015;Wood et al, 2015) or where carbonate was the dominate pool of highly reactive iron (e.g. Canfield et al, 2007;El Albani et al, 2010;Farrell et al, 2013;Jin et al, 2016;Och et al, 2013;Poulton et al, 2010;Sperling et al, 2014;Sperling et al, 2013), giving ferruginous or ferruginous and oxic iron speciation results respectively.…”

Phosphine as a Biosignature Gas in Exoplanet Atmospheres

“…We have neglected the formation of organic hazes in this work. There is evidence that such hydrocarbon hazes occurred on Earth, due to transient high levels of methane (Izon et al 2017;Zahnle et al 2019 (Arney et al 2016;Arney et al 2017). A methanogenic biosphere producing high CH4 fluxes is required to generate such high ratios; in our work, we have not considered such a biosphere.…”

Strange messenger: A new history of hydrogen on Earth, as told by Xenon

“…This suggests that Xe escape could be suppressed when conditions favor formation of high altitude hydrocarbon hazes (as seen on Titan, Triton, and Pluto). Organic hazes have been a topic of extensive speculation for Archean Earth (Domagal-Goldman et al, 2008;Zerkle et al, 2012;Hébrard and Marty, 2014;Arney et al, 2016;Izon et al, 2017). It might be tempting to link a possible hiatus in Xe isotopic evolution noted by Avice et al (2018) between 3.2 Ga and 2.7 Ga to Archean organic hazes.…”