Selenium May Support Deep Microbial Life in Earth's Continental Crust
Published:27 Jul.2021 Source:Geological Society of America
International drilling efforts over the last decades into the seafloor have provided increasing evidence for the existence of an extensive deep biosphere below the seafloor. There, circulating fluids in the sub-seafloor deliver chemical compounds from which energy is produced to fuel microbial life in such deep ecosystems. Our understanding of the role of such chemolithotrophic microbes in the continental deep biosphere, however, is much more limited due to poor accessibility.
Only a few places worldwide, mostly some of the oldest continental crust fragments such as Archean cratons, enable direct sampling of the continental deep biosphere. Such places indicate that deep-seated fractures act as fluid pathways and deliver microbially important nutrients to otherwise hostile habitats. The availability of selenium (Se) might play a crucial role in such systems because the reduction of oxidized Se species provides by far more energy than the reduction of sulfate. Hence, even small amounts of Se could potentially sustain microbial activity if the right physicochemical conditions are met.