Biosignatures of ancient microbial life are present across the igneous crust of the Fennoscandian shield

Abstract

Earth’s crust contains a substantial proportion of global biomass, hosting microbial life up to several kilometers depth. Yet, knowledge of the evolution and extent of life in this environment remains elusive and patchy. Here we present isotopic, molecular and morphological signatures for deep ancient life in vein mineral specimens from mines distributed across the Precambrian Fennoscandian shield. Stable carbon isotopic signatures of calcite indicate microbial methanogenesis. In addition, sulfur isotope variability in pyrite, supported by stable carbon isotopic signatures of methyl-branched fatty acids, suggest subsequent bacterial sulfate reduction. Carbonate geochronology constrains the timing of these processes to the Cenozoic. We suggest that signatures of an ancient deep biosphere and long-term microbial activity are present throughout this shield. We suggest that microbes may have been active in the continental igneous crust over geological timescales, and that subsurface investigations may be valuable in the search for extra-terrestrial life.

The Climates of Earth’s Next Supercontinent: Effects of Tectonics, Rotation Rate, and Insolation

“…(2008) temperature definition in a 3–D sense reveals little difference in “climatic habitability” between worlds that otherwise appear quite climatically distinct. On Earth life has been found to withstand pressures beyond those of deep sea trenches on Earth (e.g., Sharma et al., 2002; Vanlint et al., 2011), at the bottom of thick ice sheets (e.g., Griffiths et al., 2021) and in extremely deep mines (e.g., Drake et al., 2021; Lollar et al., 2019). Given enough time life has found a way to fill nearly every ecological niche on the modern Earth.…”

A glimpse of the paleome in endolithic microbial communities

“…The detected paleome signatures cannot reflect the metabolic potentials of microbes colonizing sediments about 240 million years ago, when the Upper Muschelkalk and Lower Keuper (lithostratigraphic subgroups of the Middle Triassic) were formed [92]. Our paleome signatures cannot be considered as biosignatures from ancient microbial life over geological time periods, as those identified in calcite and pyrite veins across the Precambrian Fennoscandian shield by isotopic and molecular analyses [93]. Rather carbonate bedrocks represent DNA archives that can be used to learn more about the near biological past.…”

Dissolved Microbial Methane in the Deep Crystalline Crust Fluids–Current Knowledge and Future Prospects

“…Nevertheless, the crystalline bedrock can sometimes host organic carbon (such as bitumen/seep oil) within fracture networks [41,42]. Migration of organic matter from organic-rich source rock into to fractured crystalline basement during burial heating has been suggested in localities such as the Siljan impact structure in Sweden [43] and the Bergslagen area [22,31] of the Fennoscandian shield. The bitumen and seep oil are associated with thermogenic methane but can also provide a ready energy source for microbial activity [30,41].…”

“…The importance of viral predation exerting top-down control on microbial communities in the terrestrial deep biosphere, also suggests that the predation of viruses on the microbial communities may provide an important resource of organic carbon to the deep ecosystems [28]. In addition, recent investigations of biosignatures in secondary mineral coatings and fossilized microbial remains in deep crystalline bedrock fractures of the Fennoscandian shield have revealed that microbial methanogenesis and anaerobic oxidation of methane have been widespread processes in the deep subsurface over hundreds of millions of years [22,[29][30][31].…”