title: Isotopic evidence for an aerobic nitrogen cycle in the latest Archean.
abstract: The nitrogen cycle provides essential nutrients to the biosphere, but its antiquity in modern form is unclear. In a drill core though homogeneous organic-rich shale in the 2.5-billion-year-old Mount McRae Shale, Australia, nitrogen isotope values vary from +1.0 to +7.5 per mil (per thousand) and back to +2.5 per thousand over approximately 30 meters. These changes evidently record a transient departure from a largely anaerobic to an aerobic nitrogen cycle complete with nitrification and denitrification. Complementary molybdenum abundance and sulfur isotopic values suggest that nitrification occurred in response to a small increase in surface-ocean oxygenation. These data imply that nitrifying and denitrifying microbes had already evolved by the late Archean and were present before oxygen first began to accumulate in the atmosphere.
authors.affiliation: Department of Earth and Space Sciences and Astrobiology Program, University of Washington, Seattle, WA 98195-1310, USA.
authors.forename: Jessica
authors.initials: J
authors.lastname: Garvin
authors.forename: Roger
authors.initials: R
authors.lastname: Buick
authors.forename: Ariel D
authors.initials: AD
authors.lastname: Anbar
authors.forename: Gail L
authors.initials: GL
authors.lastname: Arnold
authors.forename: Alan J
authors.initials: AJ
authors.lastname: Kaufman
mesh_terms: D000332:Aerobiosis; D000693:Anaerobiosis; D001105:Archaea / Q000378:metabolism*; D001315:Australia; D001419:Bacteria / Q000378:metabolism*; D005075:Biological Evolution; D019015:Geologic Sediments / Q000737:chemistry*; D009566:Nitrates / Q000737:chemistry / Q000378:metabolism; D009573:Nitrites / Q000737:chemistry / Q000378:metabolism; D009584:Nitrogen / Q000737:chemistry* / Q000378:metabolism*; D009586:Nitrogen Fixation; D009587:Nitrogen Isotopes / Q000032:analysis*; D009792:Oceans and Seas; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry* / Q000378:metabolism; D000644:Quaternary Ammonium Compounds / Q000737:chemistry / Q000378:metabolism; D013995:Time
chemical_list: D009566:Nitrates; D009573:Nitrites; D009587:Nitrogen Isotopes; D000644:Quaternary Ammonium Compounds; D009584:Nitrogen; D010100:Oxygen