Abiotic formation of hydrocarbons under hydrothermal conditions: Constraints from chemical and isotope data

Differentiating biotic from abiotic methane genesis in hydrothermally active planetary surfaces

“…Because of the granular texture of olivine utilized herein, the H 2 production rates from Exps. 1 and 2 are likely among the slowest for laboratory serpentinization experiments (e.g., 15,20). Although it is difficult to compare directly the laboratory H 2 production rates with rates in mid-ocean ridge systems, elevated H 2 generated primarily via serpentinization has been reported at mid-ocean ridge serpentinization localities at concentrations very similar to our reported values (3,8,12,26).…”

“…Additionally, secondary minerals such as magnetite (Fe 3 O 4 ) and/or awaruite (Ni 3 Fe) are produced during olivine hydrolysis, providing increased opportunities for FTT catalysis (13,15,(18)(19)(20)(21). Here, we evaluate the rate of abiotic CH 4 production for systems catalyzed both by chromite and secondary minerals (magnetite and awaruite) in experimental systems undergoing serpentinization at 200°C and 0.03 gigapascal (GPa), conditions similar to hydrothermally altered peridotite in midocean ridge environments on Earth or at approximately 5 km depth in the Martian subsurface.…”

Methane generation during experimental serpentinization of olivine

“…In particular, experiments using 13 C-labeled reactants to track carbon sources have shown that background sources generate methane at μmol·kg −1 levels, comparable to the concentrations reported by Oze et al (1). Furthermore, the labeled experiments show that only a small fraction of the methane produced in the experiments occurs as 13 CH 4 , demonstrating that the vast majority of the methane comes from carbon already present in reduced form at the onset of the experiments. In one experiment, for example, serpentinization of olivine at 300°C in the presence of dissolved H 13 CO 3 − yielded <2 μmol·kg −1 of 13 CH 4 , whereas most of the methane generated in the experiment was unlabeled (∼11 μmol·kg −1 12 CH 4 ).…”

“…Furthermore, the labeled experiments show that only a small fraction of the methane produced in the experiments occurs as 13 CH 4 , demonstrating that the vast majority of the methane comes from carbon already present in reduced form at the onset of the experiments. In one experiment, for example, serpentinization of olivine at 300°C in the presence of dissolved H 13 CO 3 − yielded <2 μmol·kg −1 of 13 CH 4 , whereas most of the methane generated in the experiment was unlabeled (∼11 μmol·kg −1 12 CH 4 ). Oze et al (1) reported no effort to document the source of carbon for the methane observed in their experiments, nor do they report adequate control experiments to assess background methane levels.…”

“…Methane generation during experimental serpentinization of olivine Oze et al (1) observed generation of methane (CH 4 ) during experimental serpentinization of olivine, and use the results to make inferences about sources of methane in natural serpentinites. Their data interpretation, however, is directly contradicted by results of prior studies, critically undermining the credibility of their conclusions.…”