Differentiating biotic from abiotic methane genesis in hydrothermally active planetary surfaces

Molecular hydrogen (H₂) is derived from the hydrothermal alteration of olivine-rich planetary crust. Abiotic and biotic processes consume H₂ to produce methane (CH₄); however, the extent of either process is unknown. Here, we assess the temporal dependence and limit of abiotic CH₄ related to the presence and formation of mineral catalysts during olivine hydrolysis (i.e., serpentinization) at 200?°C and 0.03 gigapascal. Results indicate that the rate of CH₄ production increases to a maximum value related to magnetite catalyzation. By identifying the dynamics of CH₄ production, we kinetically model how the H₂ to CH₄ ratio may be used to assess the origin of CH₄ in deep subsurface serpentinization systems on Earth and Mars. Based on our model and available field data, low H₂/CH₄ ratios (less than approximately 40) indicate that life is likely present and active.