Rock-hosted life through time – Integrating biosignatures of ancient and modern hydrothermal systems

Recent advances in analytical tools including more sensitive detection techniques have led to the discovery of microbial biosignatures in ultra-low biomass samples such as the oceanic lithosphere. Here, energy fluxes are low and microbial life has adapted to the slow cycling of sparsely available food and nutrient sources along cracks and fissures and the access to Earths chemical energy through water-rock interactions. Nevertheless, our understanding of the habitability of Earths lithosphere and potential connections to the surface world are still in its infancy. Rock-hosted microbes produce unique biosignatures such as diether and tetraether lipids produced by both bacteria and archaea. These lipid biomarkers can be used to trace chemo(litho)trophic life in extant, but also in past ecosystems due to their exceptional preservation as chemical fossils in mineral precipitates. Here, we present lipid data from a diverse set of past and present lithospheric habitats, ranging from the lower ocean crust to active and inactive hydrothermal vents and subsurface mantle rocks to terrestrial ophiolites in order to explore the diversity and abundance of microbes found in these systems. Furthermore, we will discuss the approaches we currently have in place to elucidate microbial metabolisms, microbe-mineral interactions and their potential roles in global geochemical cycles.