IT is unknown when life first appeared on Earth. https://ntrs.nasa.gov/search

. (2016). Rapid emergence of life shown by discovery of 3,700-million-year-old microbial structures. Nature, 537 (7621), 535-538. Rapid emergence of life shown by discovery of 3,700-million-year-old microbial structures AbstractBiological 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-Myrold 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. Keywords emergence, life, shown, discovery, rapid, 3, structures, 700, million, year, old, microbial Disciplines Medicine and Health Sciences | Social and Behavioral Sciences Publication DetailsNutman, A. P., Bennett, V. C., Friend, C. R. L., Van Kranendonk, M. J. & Chivas, A. R. (2016). Rapid emergence of life shown by discovery of 3,700-million-year-old microbial structures. Nature, 537 (7621), 535-538. 127Low deformation lacuna site 'C' preserves a 30 cm thick breccia lens in dolomite-rich 128 metasedimentary rocks is associated with dolostone (Fig. 2d) 139The barium-rich character of some layers of the dolomitic succession (up to 1 wt% BaO) now 140represented by halogen-rich barian phlogopite ± barian muscovite ± hyalophane (Extended and La anomalies and low total REE contents (Fig. 3, Extended Data Table 2 and Fig. 4). 149This REE+Y signature is preserved in even the most Ti-Al rich 'marly' layer (analysis A-2 Palaeoarchaean stromatolites (Fig. 1). 179(ii) The presence of originally low temperature dolomite, which requires microbial 180 activity for precipitation 24,25 .

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The current nomenclature for the Lewisian Gneiss Complex has evolved from lithological and structural correlations made prior to any dating. Initial (flawed) geochronological studies gave some names an apparent chronological standing but, as work advanced, fitting events into a coherent regional framework became increasingly difficult. Modern dating studies have shown that the Lewisian Gneiss Complex was progressively assembled from disparate blocks of Archaean continental crust and juvenile Proterozoic arcs, which satisfy the definition of terranes. Each terrane had its own separate accretionary and metamorphic history followed by a common history once juxtaposed against other terranes. Based on a new compilation of modern geochronology allied to the many detailed structural and metamorphic studies, this paper proposes a new systematic terminology for the Lewisian Gneiss Complex that is more applicable to this new tectonic framework.

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