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. 2020 Jun 2;11(1):2774.
doi: 10.1038/s41467-020-16493-1.

Mantle data imply a decline of oxidizable volcanic gases could have triggered the Great Oxidation

Shintaro Kadoya  1 , David C Catling  2 , Robert W Nicklas  3 , Igor S Puchtel  4 , Ariel D Anbar  5
Affiliations

Mantle data imply a decline of oxidizable volcanic gases could have triggered the Great Oxidation

Shintaro Kadoya et al. Nat Commun. .

Abstract

Aerobic lifeforms, including humans, thrive because of abundant atmospheric O2, but for much of Earth history O2 levels were low. Even after evidence for oxygenic photosynthesis appeared, the atmosphere remained anoxic for hundreds of millions of years until the ~2.4 Ga Great Oxidation Event. The delay of atmospheric oxygenation and its timing remain poorly understood. Two recent studies reveal that the mantle gradually oxidized from the Archean onwards, leading to speculation that such oxidation enabled atmospheric oxygenation. But whether this mechanism works has not been quantitatively examined. Here, we show that these data imply that reducing Archean volcanic gases could have prevented atmospheric O2 from accumulating until ~2.5 Ga with ≥95% probability. For two decades, mantle oxidation has been dismissed as a key driver of the evolution of O2 and aerobic life. Our findings warrant a reconsideration for Earth and Earth-like exoplanets.

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Conflict of interest statement

The authors declare no competing interests.

Figures

Fig. 1
Fig. 1. Evolution of the oxygen fugacity of mantle.
The oxygen fugacity (fO2) is in log10 units relative to the Fayalite–Magnetite–Quartz (FMQ) buffer. In a, we show original data of Aulbach and Stagno and Nicklas et al.. Dotted and dashed lines in a represent a linear fit for the data of Aulbach and Stagno and Nicklas et al., respectively, showing similar trends. Both datasets should converge on an average modern fO2 value inferred from mid-ocean ridge basalt (MORB). So, in b, we anchor the datasets to the MORB-inferred fO2 of the modern mantle, 0.2. Thus, 0.2 is added to Aulbach and Stagno data and −1.00 to Nicklas et al. data. The black solid line and gray shaded region in b represent the median value and 95% confidence interval of oxygen fugacity, respectively. The error bar represents uncertainty of 1σ. The gray shaded region corresponds to a variation of the slope of the linear fit, which is propagated from the variations of the samples (i.e., the error bars). Note that in b, the variation of the fO2 of the modern mantle, which is discussed later, is neglected.
Fig. 2
Fig. 2. Evolution of the dimensionless oxygenation parameter, Koxy.
Solid lines represent median values, and the shaded region bounds 5% to 95% probability quantiles. These are obtained by 10,000 times Monte-Carlo simulations. Gray dotted lines highlight Koxy = 1, above which the atmosphere is oxic; otherwise, it is anoxic. a Organic burial fraction is constant at 20%, and the secular increase in the oxygen fugacity of mantle in Fig. 1b is considered. b Both a change in organic burial fraction from Krissansen-Totton et al. and secular increase in the oxygen fugacity in Fig. 1b are considered. c Oxygen fugacity is assumed to be constant at three different levels (blue: FMQ-2, black: FMQ-1, orange: FMQ). The fluctuations come from imposed changes in organic burial fraction. In b, the parameter Koxy exceeds unity by ~2.5 Ga with >= 95% probability.
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