Deeply fractured rocks within meteorite impact structures have been hypothesized as hot spots for microbial colonization on Earth and other planetary bodies, owing to their characteristic long-term heat flow, impact-generated hydrothermal (IGH) systems with geochemical and thermal gradients, and pore space enabling microbial colonization. Biosignatures of such colonization are rare, however, and most importantly, direct geochronological evidence linking the colonization to the IGH systems are usually lacking. In addition, U–Pb dating for fracture-hosted calcite at Siljan impact structure and Rb/Sr for adularia-calcite at Lockne impact structure showed that the microbial activity was >300 and >100 Myr younger than the impact events, respectively.

In this talk, details on impact crater colonization in general, and results from our recent study of the Lappajärvi impact crater, Finland, in particular will be handled.

In the latter study we provide the first direct evidence for meteorite impact-related microbial colonization on Earth by using coupled microscale secondary-ion mass spectrometry (SIMS) biosignature detection (δ13Ccalcite and δ34Spyrite, clumped isotope analysis and U-Pb dating of vug- and fracture-filling mineral assemblages. The earliest mineral precipitation at habitable temperatures for life featured substantially 34S-depleted pyrite consistent with microbial sulfate reduction, and occurred in the first few million years after the impact event. Later stages of mineral precipitation featured δ13Ccalcite values diagnostic for anaerobic microbial consumption and production of methane. These new groundbreaking insights into microbial colonization of impact structures on Earth have implications for the emergence of life on Early Earth and beyond, particularly as deep biosphere habitats in impact structures are considered favorable targets for Mars exploration for signs of extinct life.