title: Rapid emergence of life shown by discovery of 3,700-million-year-old microbial structures.
abstract: Biological activity is a major factor in Earth's chemical cycles, including facilitating CO2sequestration and providing climate feedbacks. Thus a key question in Earth's evolution is when did life arise and impact hydrosphere-atmosphere-lithosphere chemical cycles? Until now, evidence for the oldest life on Earth focused on debated stable isotopic signatures of 3,800-3,700 million year (Myr)-old metamorphosed sedimentary rocks and minerals from the Isua supracrustal belt (ISB), southwest Greenland. Here we report evidence for ancient life from a newly exposed outcrop of 3,700-Myr-old metacarbonate rocks in the ISB that contain 1-4-cm-high stromatolites-macroscopically layered structures produced by microbial communities. The ISB stromatolites grew in a shallow marine environment, as indicated by seawater-like rare-earth element plus yttrium trace element signatures of the metacarbonates, and by interlayered detrital sedimentary rocks with cross-lamination and storm-wave generated breccias. The ISB stromatolites predate by 220 Myr the previous most convincing and generally accepted multidisciplinary evidence for oldest life remains in the 3,480-Myr-old Dresser Formation of the Pilbara Craton, Australia. The presence of the ISB stromatolites demonstrates the establishment of shallow marine carbonate production with biotic CO2sequestration by 3,700 million years ago (Ma), near the start of Earth's sedimentary record. A sophistication of life by 3,700 Ma is in accord with genetic molecular clock studies placing life's origin in the Hadean eon (>4,000 Ma).
authors: GeoQuEST Research Centre, School of Earth &Environmental Sciences, University of Wollongong, Wollongong, New South Wales 2522, Australia.|Australian Centre for Astrobiology, University of New South Wales, Kensington, New South Wales 2052, Australia.
authors: Allen P
authors: AP
authors: Nutman
authors: Research School of Earth Sciences, Australian National University, Canberra, Australian Capital Territory 0200, Australia.
authors: Vickie C
authors: VC
authors: Bennett
authors: Glendale, Tiddington, Oxon, Oxford OX9 2LQ, UK.
authors: Clark R L
authors: CR
authors: Friend
authors: Australian Centre for Astrobiology, University of New South Wales, Kensington, New South Wales 2052, Australia.|School of Biological, Earth and Environmental Sciences, University of New South Wales, Kensington, New South Wales 2052, Australia.|Australian Research Council Centre of Excellence for Core to Crust Fluid Systems, School of Biological, Earth and Environmental Sciences, University of New South Wales, Kensington, New South Wales 2052, Australia.
authors: Martin J
authors: MJ
authors: Van Kranendonk
authors: GeoQuEST Research Centre, School of Earth &Environmental Sciences, University of Wollongong, Wollongong, New South Wales 2522, Australia.
authors: Allan R
authors: AR
authors: Chivas
mesh_terms: D059001:Aquatic Organisms; D001315:Australia; D005580:Fossils; D019015:Geologic Sediments / Q000382:microbiology*; D019369:Life; D000069497:Origin of Life; D012623:Seawater / Q000382:microbiology*; D013997:Time Factors