Recurring discoveries of abiotic methane in gas seeps and springs in ophiolites and peridotite massifs worldwide raised the question of where, in which rocks, methane was generated. Answers will impact the theories on life origin related to serpentinization of ultramafic rocks, and the origin of methane on rocky planets. Here we document, through molecular and isotopic analyses of gas liberated by rock crushing, that among the several mafic and ultramafic rocks composing classic ophiolites in Greece, i.e., serpentinite, peridotite, chromitite, gabbro, rodingite and basalt, only chromitites, characterized by high concentrations of chromium and ruthenium, host considerable amounts of ¹³C-enriched methane, hydrogen and heavier hydrocarbons with inverse isotopic trend, which is typical of abiotic gas origin. Raman analyses are consistent with methane being occluded in widespread microfractures and porous serpentine- or chlorite-filled veins. Chromium and ruthenium may be key metal catalysts for methane production via Sabatier reaction. Chromitites may represent source rocks of abiotic methane on Earth and, potentially, on Mars.

Here we present digitization and analysis of the thermal springs of the world dataset compiled by Gerald Ashley Waring in 1965 into a collection of analog maps. We obtain the geographic coordinates of ~6,000 geothermal spring areas, including complementary data (e.g., temperature, total dissolved solids, flow rate), making them available in electronic format. Using temperature and flow rate, we derive the heat discharged from 1483 thermal spring areas (between ~10⁻⁵ and ~10³MW, with a median value of ~0.5 MW and ~8300 MW in total). We integrate this data set with other global data sets to study the relationship between thermalism and endogenous and exogenous factors with a supervised machine learning algorithm. This analysis confirms a dominant role of the terrestrial heat flow, topography, volcanism and extensional tectonics. This data set offers new insights and will boost future studies in geothermal energy exploration.

Earth’s hydrocarbon degassing through gas-oil seeps, mud volcanoes and diffuse microseepage is a major natural source of methane (CH₄) to the atmosphere. While carbon dioxide degassing is typically associated with extensional tectonics, volcanoes, and geothermal areas, CH₄ seepage mostly occurs in petroleum-bearing sedimentary basins, but the role of tectonics in degassing is known only for some case studies at local scale. Here, we perform a global scale geospatial analysis to assess how the presence of hydrocarbon fields, basin geodynamics and the type of faults control CH₄ seepage. Combining georeferenced data of global inventories of onshore seeps, faults, sedimentary basins, petroleum fields and heat flow, we find that hydrocarbon seeps prevail in petroleum fields within convergent basins with heat flow ≤ 98 mW m⁻², and along any type of brittle tectonic structure, mostly in reverse fault settings. Areas potentially hosting additional seeps and microseepage are identified through a global seepage favourability model.