Isotopic evidence for an aerobic nitrogen cycle in the latest Archean.
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.
Garvin
Jessica
J
Department of Earth and Space Sciences and Astrobiology Program, University of Washington, Seattle, WA 98195-1310, USA.
Buick
Roger
R
Anbar
Ariel D
AD
Arnold
Gail L
GL
Kaufman
Alan J
AJ
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
D009566:Nitrates; D009573:Nitrites; D009587:Nitrogen Isotopes; D000644:Quaternary Ammonium Compounds; D009584:Nitrogen; D010100:Oxygen