The taphonomic fate of biominerals in hydrothermal sulfide systems – implications for the reconstruction of microbial life in deep time

Hydrothermal sulfide systems are among the most ancient habitats on Earth and are widely considered potential sites for the emergence of life. Deposits from such settings are thus of great evolutionary significance, but the geobiology of our planet’s most ancient hydrothermal sulfide systems remains largely unexplored. This is mainly due to a limited understanding of the formation and preservation of microbial biosignatures in such settings, particularly over geological timescales. Here we present our strategy to explore the geobiology of ancient hydrothermal sulfides by integrating analytical and experimental methods from geology, geochemistry, and microbiology. Specifically, we expose synthetic and biogenic Fe-minerals to physical and chemical conditions relevant to microbial niches in hydrothermal environments on early Earth (<121°C, anoxic, sulfidic). We characterize the resulting precipitates with analytical imaging techniques, mineralogical methods, and geochemical approaches (e.g., SEM-EDS, µXRD, Raman spectroscopy, sequential Fe extraction). By comparing the observed characteristics with those of minerals in modern and ancient hydrothermal sulfide deposits, we are able to identify primary biogenic mineral precipitates and their transformation products. This integrative approach will allow us to develop an in-depth understanding of the formation and preservation of biosignatures in hydrothermal environments. This, in turn, is critical for the reconstruction of microbial life in deep time.