Biological activity is a major factor in Earth’s chemical cycles, including facilitating CO2 sequestration 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 minerals1,2 from the Isua supracrustal belt (ISB), southwest Greenland3. 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, Australia4,5. The presence of the ISB stromatolites demonstrates the establishment of shallow marine carbonate production with biotic CO2 sequestration 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)6.
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Support provided by Australian Research Council grant DP120100273 and the GeoQuEST Research Centre, University of Wollongong (UOW). D. Wheeler, UOW, is thanked for technical assistance in carbon and oxygen isotopic analysis. L. Kinsley, Research School of Earth Sciences, Australian National University is thanked for assistance with LA-ICP-MS data acquisition. D. Adams of the Department of Earth & Planetary Sciences, Macquarie University is thanked for assistance with mineral analyses. M. Nancarrow of the Electron Microscopy Centre, UOW is thanked for assistance with SEM-imaging and mineral analyses. P. Gadd of the Australian Nuclear Science and Technology Organisation is thanked for undertaking ITRAX analyses. M.J.V.K. acknowledges support by the University of New South Wales and the Australian Research Council Centre of Excellence for Core to Crust Fluid Systems (CCFS). This is contribution 837 from the ARC Centre of Excellence for Core to Crust Fluid Systems (http://www.ccfs.mq.edu.au). Some analytical data were obtained using instrumentation funded by DEST Systemic Infrastructure Grants, ARC LIEF, NCRIS/Auscope industry partners and Macquarie University.
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Nature Geoscience (2018)