Implications of a 3.472-3.333 Gyr-old subaerial microbial mat from the Barberton greenstone belt, South Africa for the UV environmental conditions on the early Earth
In: ISSN: 0962-8436 ; EISSN: 1471-2970, 2006
academicJournal
Zugriff:
Modelling suggests that the UV radiation environment of the early Earth, with DNA weighted irradiances of about three orders of magnitude greater than those at present, was hostile to life forms at the surface, unless they lived in specific protected habitats. However, we present empirical evidence that challenges this commonly held view. We describe a well-developed microbial mat that formed on the surface of volcanic littoral sediments in an evaporitic environment in a 3.5-3.3Ga-old formation from the Barberton greenstone belt. Using a multiscale, multidisciplinary approach designed to strongly test the biogenicity of potential microbial structures, we show that the mat was constructed under flowing water by 0.25 microm filaments that produced copious quantities of extracellular polymeric substances, representing probably anoxygenic photosynthesizers. Associated with the mat is a small colony of rods-vibroids that probably represent sulphur-reducing bacteria. An embedded suite of evaporite minerals and desiccation cracks in the surface of the mat demonstrates that it was periodically exposed to the air in an evaporitic environment. We conclude that DNA-damaging UV radiation fluxes at the surface of the Earth at this period must either have been low (absorbed by CO2, H2O, a thin organic haze from photo-dissociated CH4, or SO2 from volcanic outgassing; scattered by volcanic, and periodically, meteorite dust, as well as by the upper layers of the microbial mat) and/or that the micro-organisms exhibited efficient gene repair/survival strategies.
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Implications of a 3.472-3.333 Gyr-old subaerial microbial mat from the Barberton greenstone belt, South Africa for the UV environmental conditions on the early Earth
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Autor/in / Beteiligte Person: | Westall, Frances ; De Ronde, Cornel E. J ; Southam, Gordon ; Grassineau, Nathalie ; Colas, Maggy ; Cockell, Charles ; H.Lammer, Helmut ; Centre de biophysique moléculaire (CBM) ; Université d'Orléans (UO)-Institut National de la Santé et de la Recherche Médicale (INSERM)-Centre National de la Recherche Scientifique (CNRS)-Institut de Chimie du CNRS (INC) ; Institute of Geological and Nuclear Sciences (IGNS) ; Department of Earth Sciences London, ON ; University of Western Ontario (UWO) ; Royal Holloway University of London (RHUL) ; Centre de recherches sur les matériaux à haute température (CRMHT) ; Centre National de la Recherche Scientifique (CNRS) ; Planetary and Space Sciences Research Institute Milton Keynes (PSSRI) ; Centre for Earth, Planetary, Space and Astronomical Research Milton Keynes (CEPSAR) ; The Open University Milton Keynes (OU)-The Open University Milton Keynes (OU) ; Space Research Institute of Austrian Academy of Sciences (IWF) ; Austrian Academy of Sciences (OeAW) |
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Zeitschrift: | ISSN: 0962-8436 ; EISSN: 1471-2970, 2006 |
Veröffentlichung: | HAL CCSD ; Royal Society, The, 2006 |
Medientyp: | academicJournal |
DOI: | 10.1098/rstb.2006.1896 |
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