Abiogenic methanogenesis during experimental komatiite serpentinization: Implications for the evolution of the early Precambrian atmosphere

Abiotic methane formation during experimental serpentinization of olivine

“…Results of this study as well as those of other studies using 13 Clabeled carbon sources (17)(18)(19)28) for experiments performed at 200°C to 230°C) (Table 1), the lower levels of background sources observed here are likely attributable to extensive efforts to purify the mineral reactants and avoid introduction of potential organic contaminants into the reaction materials (29) as well as more extensive olivine reaction in the other studies. Oze et al (34) argue that carbonate undersaturation led to higher generation rates of H 2 and abiotic CH 4 in their experiments, but there is no logical reason to expect that undersaturation would enhance the rate of carbon reduction.…”

“…The results reported here are consistent with previous laboratory studies performed with serpentinite-related minerals at temperatures ≥300°C that show both limited abiotic synthesis of CH 4 and relatively high levels of CH 4 from background sources (17)(18)(19)(20)(21)28). However, the results disagree with other recent reports, where the CH 4 produced during experimental reaction of olivine with aqueous solutions has been interpreted to be predominantly derived from abiotic reduction of dissolved inorganic carbon (22)(23)(24)(25).…”

“…Several subsequent experimental studies confirmed that abiotic reduction of dissolved CO 2 to CH 4 is sluggish at temperatures as low as 300°C, even in the presence of highly elevated H 2 concentrations, except when NiFe alloy was present (16,(18)(19)(20)(21). Additional experiments with 13 C-labeled inorganic carbon compounds also confirmed that background sources are a ubiquitous contributor to CH 4 in experimental fluidrock studies using olivine or other minerals, with abundance that often far exceeds that of bona fide synthesis products (18,19,28).…”

“…These experiments were performed using methods very similar to those of this study, except that the reaction vessel was periodically rotated during heating. After heating for [22][23][24][25][26][27][28][29][30][31][32][33][34][35][36] (Table 1). However, isotopic labeling indicated that the CH 4 in our experiments was not derived from reduction of dissolved inorganic carbon but instead, was derived entirely from background sources (i.e., composed of 99 mol % 12 CH 4 ).…”

Hydrogen-rich hydrothermal environments in the Hadean ocean inferred from serpentinization of komatiites at 300 °C and 500 bar

“…Of course, komatiite-associated hydrothermal activity does not occur in the modern ocean; thus, the H 2 generation potential of komatiites during serpentinization can only be experimentally estimated through simulated hydrothermal fluid-rock reactions under high-temperature and high-pressure conditions, as previously conducted to reconstruct modern (Seyfried 1987;Seyfried et al 2007;McCollom et al 2010;Kato et al 2013;Suzuki et al 2015a, b), ancient (Yoshizaki et al 2009;Lazar et al 2012;, and even extraterrestrial subseafloor hydrothermal systems Sekine et al 2015). Yoshizaki et al (2009) confirmed hydrogen generation by a preliminary, ongoing experiment using komatiite and pure water (Yoshizaki et al 2009).…”