A geochemical gradient established by mixing between reduced, hyperalkaline (pH > 11), H2‐rich fluids generated through the process of serpentinization and surrounding surface water (pH ∼ 8) in the Samail Ophiolite of Oman provides an opportunity to characterize the geochemical and biological factors that influence the distribution of H2 oxidizing chemotrophs, hydrogenotrophs. In this study, 16S rRNA gene amplicon sequencing was implemented to characterize hydrogenotrophs in sediments underlying surface expressed serpentinized fluids in Oman. Hydrogenotroph phylotype distribution was evaluated as functions of chemical energy supplies for their given metabolic redox reactions. Through this approach, it was discovered that hydrogenotrophic taxa are likely constrained to sediments with overlying fluids that have <∼60 μm O2, including microorganisms of the genus, Hydrogenophaga. Sulfate reducers of the family, Thermodesulfovibrionaceae, likely require >∼10 μm SO4−2 for survival. In sediments with fluids having >∼10 μm SO4−2, sulfate reducers likely outcompete microorganisms of the methanogen genus, Methanobacterium, for H2. Additionally, differences in distribution between Thermodesulfovibrionaceae and Methanobacterium may be driven by the availability of electron acceptors and the redox reaction that is most energy yielding in the fluid. Taken together, observations from the Oman geochemical gradient result in a hydrogenotroph niche model that can be used to evaluate global distribution patterns of hydrogenotrophs in continental serpentinized fluids. On a global scale, based on previous studies, Methanobacterium is constrained to fluids that have <∼10 μm SO4−2.

No abstract

At present, molecular hydrogen (H2) produced through Fe(II) oxidation during serpentinization of ultramafic rocks represents a small fraction of the global sink for O2 due to limited exposures of ultramafic rocks. In contrast, ultramafic rocks such as komatiites were much more common in the Early Earth and H2 production via serpentinization was a likely factor in maintaining an O2-free atmosphere throughout most of the Archean. Using thermodynamic simulations, this work quantifies the global O2 consumption attributed to serpentinization during the past 3.5 billion years. Results show that H2 generation is strongly dependent on rock compositions where serpentinization of more magnesian lithologies generated substantially higher amounts of H2. Consumption of >2 Tmole O2 yr−1 via low-temperature serpentinization of Archean continents and seafloor is possible. This O2 sink diminished greatly towards the end of the Archean as ultramafic rocks became less common and helped set the stage for the Great Oxidation Event.

Serpentinizing systems, established when aqueous planetary fluids react with ultramafic (UM) rocks, produce significant quantities of dihydrogen (H 2 ) across a large range of geochemical conditions. This H 2 actively supports chemosynthetic communities on Earth (

One of the most habitable environments in the Solar System outside of Earth may exist underneath the ice on Europa. In the near future, our best chance to look for chemical signatures of a habitable environment (or life itself) will likely be at the inhospitable icy surface. Therefore, it is important to understand the ability of organic signatures of life and life itself to persist under simulated europan surface conditions. Toward that end, this work examined the UV photolysis of Bacillus subtilis spores and their chemical marker dipicolinic acid (DPA) at temperatures and pressures relevant to Europa. In addition, inactivation curves for the spores at 100 K, 100 K covered in one micron of ice, and 298 K were measured to determine the probability for spore survival at the surface. Fourier transform infrared spectra of irradiated DPA showed a loss of carboxyl groups to CO2 as expected but unexpectedly showed significant opening of the heterocyclic ring, even for wavelengths>200 nm. Both DPA and B. subtilis spores showed identical unknown spectral bands of photoproducts after irradiation, further highlighting the importance of DPA in the photochemistry of spores. Spore survival was enhanced at 100 K by ∼5× relative to 298 K, but 99.9% of spores were still inactivated after the equivalent of ∼25 h of exposure on the europan surface.

Several moons in the outer solar system host liquid water oceans. A key next step in assessing the habitability of these ocean worlds is to determine whether life’s elemental and energy requirements are also met. Phosphorus is required by all known life and is often limited to biological productivity in Earth’s oceans. This raises the possibility that its availability may limit the abundance or productivity of Earth-like life on ocean worlds. To address this potential problem, here we calculate the equilibrium dissolved phosphate concentrations associated with the reaction of water and rocks—a key driver of ocean chemical evolution—across a broad range of compositional inputs and reaction conditions. Equilibrium dissolved phosphate concentrations range from 10−11 to 10−1 mol/kg across the full range of carbonaceous chondrite compositions and reaction conditions considered, but are generally > 10−5 mol/kg for most plausible scenarios. Relative to the phosphate requirements and uptake kinetics of microorganisms in Earth’s oceans, such concentrations would be sufficient to support initially rapid cell growth and construction of global ocean cell populations larger than those observed in Earth’s deep oceans.

No abstract

Putative alkaline hydrothermal systems on Noachian Mars were potentially habitable environments for microorganisms. However, the types of reactions that could have fueled microbial life in such systems and the amount of energy available from them have not been quantitatively constrained. In this study, we use thermodynamic modeling to calculate which catabolic reactions could have supported ancient life in a saponite precipitating hydrothermal vent system in the Eridania basin on Mars. To further evaluate what this could mean for microbial life, we evaluated the energy potential of an analogue site in Iceland, the Strytan Hydrothermal Field (SHF). Results show that out of the 85 relevant redox reactions that were considered, the highest energy yielding reactions in the Eridania hydrothermal system were dominated by methane formation. By contrast, Gibbs energy calculations carried out for Strytan indicate that the most energetically favorable reactions are CO2 and O2 reduction coupled to H2 oxidation. In particular, our calculations indicate that an ancient hydrothermal system within the Eridania basin could have been a habitable environment for methanogens using NH4+ as an electron acceptor. Differences in Gibbs energies between the two systems were largely determined by oxygen; its presence on Earth and absence on Mars. However, Strytan can serve as a useful analogue for Eridania when studying methane producing reactions that do not involve O2.