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

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.

Time-resolved comparative molecular evolution of oxygenic photosynthesis

“…It also explains why none of the groups of extant photosynthetic bacteria appear to be older than the earliest geochemical evidence for photosynthesis or hardly older than the GOE. The presented data is also consistent with recent studies of the oxygenation of the planet, which suggests that even if photosynthetic O 2 evolution started as early as the oldest rocks, the properties of early Earth biogeochemistry would have maintained very low concentrations of O 2 over the Archean [ [70] , [71] , [72] ].…”

Carbon cycle inverse modeling suggests large changes in fractional organic burial are consistent with the carbon isotope record and may have contributed to the rise of oxygen

“…This suggests that while it is possible to construct an organic burial history consistent with the isotope record than can account for the anoxic–oxic transition at the GOE, declining oxygen sinks may have also contributed. Indeed, there is evidence for a secular oxidation of the upper mantle since the Archean, which would imply elevated fluxes of oxygen‐consuming gases on the early Earth (Aulbach & Stagno, 2016 ; Kadoya et al., 2020 ; Nicklas et al., 2019 ).…”

Mercury abundance and isotopic composition indicate subaerial volcanism prior to the end-Archean “whiff” of oxygen

“…Such gas emissions are short-lived compared to the much longer effect of weathering fresh volcanic rock (42). The cessation of intense volcanism would thus have switched off this kinetically rapid O 2 sink, thereby promoting O 2 accumulation (12). On longer time scales, weathering and mobilization of nutrients would have gained prominence and enhanced biological productivity through the whiff interval.…”

“…1), peaking where oxygenation proxies such as Mo and Hg abundance are highest. So, while saturation of oxygen sinks is often regarded as the primary cause of the GOE (12), it seems that in the case of this pre-GOE oxygenation event a contributing factor may have also been volcanic-sourced phosphorus fertilization of biogenic oxygen production. While the Mt.…”

“…The consumption of O 2 is also affected by volcanism because reaction with volcanic gases provides a long-term sink for atmospheric O 2 (e.g., ref. 11), which might have diminished in strength over time (12,13). Indeed, periods of Neoarchean subaerial volcanism roughly coincide with the hypothesized O 2 whiffs and accompanying euxinic (sulfide-rich) events (14,15), but cause-effect relationships between these events are so far unclear.…”