Re-evaluation of Endolithic Microfossils in Thuringian and Arnstein Basalt – Implications for Astrobiology
2024
Strömbäck, Dan
The presence of fossilised fungi within deep crust is established, with evidence of continental deep subsurface fossils from 400 Ma and oceanic basaltic crust containing fossils from around 81 Ma. The Ongeluk Formation contains putative fungus fossils reaching 2.4 Ga. The resulting gap of 2 billion years raises questions regarding the history of fungi, in particular the lack of clear fossils in ophiolites, sections of layered basalts from mid-ocean ridges. Devonian samples from two ophiolites in Arnstein and Thuringia, Germany, previously found to contain filaments of microorganisms with uncertain biological affinity, were investigated using environmental scanning electron microscopy, Raman spectroscopy, confocal microscopy, widefield microscopy, and optical light microscopy. EDS analyses of several structures revealed high carbon content and clay minerals, pointing to remineralization of organic content and biological origin. Raman spectroscopy revealed carbon coincident with iron oxides. Observed filamentous structures with similar chemical compositions but different morphology and lifestyles may represent closely related but separate taxa of microorganisms. Chemical content and morphologies resembling sporophores and hyphae point to the presence of fungi, shedding new light on many of the previously undetermined fossils and plausibly narrowing the fossil gap of oceanic deep subsurface fungi by at least 300 million years. As astrobiological missions on Mars are under way, particularly with the rover Perseverance, research focuses on sedimentary rocks. With a plausible presence of several microorganisms in volcanic basalts, these environments should be seriously considered as candidates for investigating microbial evidence on Mars.
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