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      Organo-mineral associations in chert of the 3.5 Ga Mount Ada Basalt raise questions about the origin of organic matter in Paleoarchean hydrothermally influenced sediments

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          Abstract

          Hydrothermal and metamorphic processes could have abiotically produced organo-mineral associations displaying morphological and isotopic characteristics similar to those of fossilized microorganisms in ancient rocks, thereby leaving false-positive evidence for early life in the geological record. Recent studies revealed that geologically-induced alteration processes do not always completely obliterate all molecular information about the original organic precursors of ancient microfossils. Here, we report the molecular, geochemical, and mineralogical composition of organo-mineral associations in a chert sample from the ca. 3.47 billion-year-old (Ga) Mount Ada Basalt, in the Pilbara Craton, Western Australia. Our observations indicate that the molecular characteristics of carbonaceous matter are consistent with hydrothermally altered biological organics, although significantly distinct from that of organic microfossils discovered in a chert sample from the ca. 3.43 Ga Strelley Pool Formation in the same area. Alternatively, the presence of native metal alloys in the chert, previously believed to be unstable in such hydrothermally influenced environments, indicates strongly reducing conditions that were favorable for the abiotic formation of organic matter. Drawing definitive conclusions about the origin of most Paleoarchean organo-mineral associations therefore requires further characterization of a range of natural samples together with experimental simulations to constrain the molecular composition and geological fate of hydrothermally-generated condensed organics.

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          Inter-laboratory note. Laser ablation inductively coupled plasma mass spectrometric transient signal data acquisition and analyte concentration calculation

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            Questioning the evidence for Earth's oldest fossils.

            Structures resembling remarkably preserved bacterial and cyanobacterial microfossils from about 3,465-million-year-old Apex cherts of the Warrawoona Group in Western Australia currently provide the oldest morphological evidence for life on Earth and have been taken to support an early beginning for oxygen-producing photosynthesis. Eleven species of filamentous prokaryote, distinguished by shape and geometry, have been put forward as meeting the criteria required of authentic Archaean microfossils, and contrast with other microfossils dismissed as either unreliable or unreproducible. These structures are nearly a billion years older than putative cyanobacterial biomarkers, genomic arguments for cyanobacteria, an oxygenic atmosphere and any comparably diverse suite of microfossils. Here we report new research on the type and re-collected material, involving mapping, optical and electron microscopy, digital image analysis, micro-Raman spectroscopy and other geochemical techniques. We reinterpret the purported microfossil-like structure as secondary artefacts formed from amorphous graphite within multiple generations of metalliferous hydrothermal vein chert and volcanic glass. Although there is no support for primary biological morphology, a Fischer--Tropsch-type synthesis of carbon compounds and carbon isotopic fractionation is inferred for one of the oldest known hydrothermal systems on Earth.
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              GeoReM: A New Geochemical Database for Reference Materials and Isotopic Standards

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                Author and article information

                Contributors
                julien.alleon@gmail.com
                Journal
                Sci Rep
                Sci Rep
                Scientific Reports
                Nature Publishing Group UK (London )
                2045-2322
                13 November 2019
                13 November 2019
                2019
                : 9
                : 16712
                Affiliations
                [1 ]ISNI 0000 0001 2341 2786, GRID grid.116068.8, Department of Earth, Atmospheric and Planetary Sciences, , Massachusetts Institute of Technology, ; Cambridge, Massachusetts USA
                [2 ]ISNI 0000000107068890, GRID grid.20861.3d, Jet Propulsion Laboratory, , California Institute of Technology, ; Pasadena, California USA
                [3 ]ISNI 0000 0001 2341 2786, GRID grid.116068.8, Department of Materials Science and Engineering, , Massachusetts Institute of Technology, ; Cambridge, Massachusetts USA
                [4 ]ISNI 0000 0000 9195 2461, GRID grid.23731.34, GFZ German Research Centre for Geosciences, ; Potsdam, Germany
                [5 ]ISNI 0000 0001 2165 4204, GRID grid.9851.5, Present Address: Now at Institute of Earth Sciences, , University of Lausanne, ; Lausanne, Switzerland
                Author information
                http://orcid.org/0000-0003-4148-2424
                Article
                53272
                10.1038/s41598-019-53272-5
                6853986
                31723181
                ba41ca69-795e-4046-b862-357fb97bcb12
                © The Author(s) 2019

                Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.

                History
                : 29 May 2019
                : 30 October 2019
                Funding
                Funded by: FundRef https://doi.org/10.13039/100000893, Simons Foundation;
                Award ID: 290361
                Award ID: 290361
                Award Recipient :
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                © The Author(s) 2019

                Uncategorized
                palaeontology,carbon cycle
                Uncategorized
                palaeontology, carbon cycle

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