Differentiating biotic from abiotic methane genesis in hydrothermally active planetary surfaces

Abstract

Molecular hydrogen (H 2) is derived from the hydrothermal alteration of olivine-rich planetary crust. Abiotic and biotic processes consume H 2 to produce methane (CH 4); however, the extent of either process is unknown. Here, we assess the temporal dependence and limit of abiotic CH 4 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 CH 4production increases to a maximum value related to magnetite catalyzation. By identifying the dynamics of CH 4 production, we kinetically model how the H 2 to CH 4 ratio may be used to assess the origin of CH 4 in deep subsurface serpentinization systems on Earth and Mars. Based on our model and available field data, low H 2/CH 4 ratios (less than approximately 40) indicate that life is likely present and active.