Methods and Approaches for Biogenicity Determination in Geological Samples - Implications for Extraterrestrial Search for Life

Sammanfattning: For a better understanding of how to search for an extraterrestrial life, scientists study hidden biospheres on Earth. The subseafloor crust is recognized as a vast microbial habitat and it is hypothesized that extremophilic microorganisms, occurring there, can be the first living organisms on Earth. Those extremophiles does not require oxygen due their ability to derive bioavailable energy from fluid-rock interactions, resembling conditions on Mars. Hence, in this study, geological samples from such environments are analysed. Overall, this report examines a concept of biogenicity and evaluates a set of methods used for the determination of biologic origin. Fossilized microbial remains were discovered in unconsolidated sediments from the volcaniclastic apron of Gran Canaria and in aragonite veins in ultramafic rocks from the North Pond at the Mid-Atlantic Ridge. Mentioned sediments and rocks were collected during Ocean Drilling Program (ODP) Leg 157 and 209. The fossil record from Gran Canaria is consistent with Foraminifera. The microbial remains from North Pond are consistent with Frutexites microstromatolites. Both fossilized communities have characteristic compositions associated with carbonaceous matter (CM) and different configurations of trace elements such as Si, Al, Mg, Mn, Ni, Fe, and Co. This study confirms the biologic origin of the fossilized remains and shows that the applied methods are suitable for astrobiological application.