Deep microbial colonization during impact-generated hydrothermal circulation at the Lappajärvi impact structure, Finland

Deeply fractured rocks of meteorite impact structures have been hypothesized as hot spots for microbial colonization on Earth and other planetary bodies. Biosignatures of such colonization are rare, however, and most importantly, direct geochronological evidence linking the colonization to the impact-generated hydrothermal systems are completely lacking. Here we provide timing constraints to microbial colonization of the 77.85 ± 0.78 Ma old Lappajärvi impact structure, Finland, by using coupled microscale stable isotope biosignature detection and radioisotopic dating of vug- and fracture-filling assemblages in impactites. The first detected mineral precipitation at habitable temperatures for life (47.0 ± 7.1 °C) occurred at 73.6 ± 2.2 Ma and featured substantially 34 S-depleted pyrite consistent with microbial sulfate reduction. Later stages of vug-mineral precipitation occurred more than 10 Myr later, at gradually lower temperatures, and featured δ 13 C calcite values diagnostic for both anaerobic microbial consumption and production of methane. These insights confirm the capacity of medium-sized (and large) meteorite impacts to generate long-lasting hydrothermal systems, enabling microbial colonization as the crater cools to ambient conditions, an effect that may have important implications for the emergence of life on Earth and beyond.