@article{82bff0061d394cd98a21f0becf7c3a77, title = "Reduction spheroids preserve a uranium isotope record of the ancient deep continental biosphere", abstract = "Life on Earth extends to several kilometres below the land surface and seafloor. This deepbiosphere is second only to plants in its total biomass, is metabolically active and diverse, andis likely to have played critical roles over geological time in the evolution of microbialdiversity, diagenetic processes and biogeochemical cycles. However, these roles are obscuredby a paucity of fossil and geochemical evidence. Here we apply the recently developeduranium-isotope proxy for biological uranium reduction to reduction spheroids in continentalrocks (red beds). Although these common palaeo-redox features have previously beensuggested to reflect deep bacterial activity, unequivocal evidence for biogenicity has beenlacking. Our analyses reveal that the uranium present in reduction spheroids is isotopicallyheavy, which is most parsimoniously explained as a signal of ancient bacterial uraniumreduction, revealing a compelling record of Earth’s deep biosphere.", author = "Sean McMahon and Ashleigh Hood and John Parnell and Stephen Bowden", year = "2018", month = "10", day = "29", doi = "10.1038/s41467-018-06974-9", language = "English", volume = "9", journal = "Nature Communications", issn = "2041-1723", publisher = "Nature Publishing Group", }