Ancient micrometeorites suggestive of an oxygen-rich Archaean upper atmosphere

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dc.contributor.authorTompkins, AGen_AU
dc.contributor.authorBowlt, Len_AU
dc.contributor.authorGenge, Men_AU
dc.contributor.authorWilson, SAen_AU
dc.contributor.authorBrand, HEAen_AU
dc.contributor.authorWykes, JLen_AU
dc.date.accessioned2021-12-07T21:49:57Zen_AU
dc.date.available2021-12-07T21:49:57Zen_AU
dc.date.issued2016-05-11en_AU
dc.date.statistics2021-11-11en_AU
dc.description.abstractIt is widely accepted that Earth’s early atmosphere contained less than 0.001 per cent of the present-day atmospheric oxygen (O2) level, until the Great Oxidation Event resulted in a major rise in O2 concentration about 2.4 billion years ago1. There are multiple lines of evidence for low O2 concentrations on early Earth, but all previous observations relate to the composition of the lower atmosphere2 in the Archaean era; to date no method has been developed to sample the Archaean upper atmosphere. We have extracted fossil micrometeorites from limestone sedimentary rock that had accumulated slowly 2.7 billion years ago before being preserved in Australia’s Pilbara region. We propose that these micrometeorites formed when sand-sized particles entered Earth’s atmosphere and melted at altitudes of about 75 to 90 kilometres (given an atmospheric density similar to that of today3). Here we show that the FeNi metal in the resulting cosmic spherules was oxidized while molten, and quench-crystallized to form spheres of interlocking dendritic crystals primarily of magnetite (Fe3O4), with wüstite (FeO)+metal preserved in a few particles. Our model of atmospheric micrometeorite oxidation suggests that Archaean upper-atmosphere oxygen concentrations may have been close to those of the present-day Earth, and that the ratio of oxygen to carbon monoxide was sufficiently high to prevent noticeable inhibition of oxidation by carbon monoxide. The anomalous sulfur isotope (Δ33S) signature of pyrite (FeS2) in seafloor sediments from this period, which requires an anoxic surface environment4, implies that there may have been minimal mixing between the upper and lower atmosphere during the Archaean. © 2016 Macmillan Publishers Limiteden_AU
dc.identifier.citationTomkins, A. G., Bowlt, L., Genge, M., Wilson, S. A., Brand, H. E. A. & Wykes, J. L. (2016). Ancient micrometeorites suggestive of an oxygen-rich Archaean upper atmosphere. Nature, 533(7602), 235-238. doi:10.1038/nature17678en_AU
dc.identifier.issn0028-0836en_AU
dc.identifier.issue7602en_AU
dc.identifier.journaltitleNatureen_AU
dc.identifier.pagination235-238en_AU
dc.identifier.urihttps://doi.org/10.1038/nature17678en_AU
dc.identifier.urihttps://apo.ansto.gov.au/dspace/handle/10238/12375en_AU
dc.identifier.volume533en_AU
dc.language.isoenen_AU
dc.publisherSpringer Natureen_AU
dc.subjectAtmospheric chemistryen_AU
dc.subjectEarth atmosphereen_AU
dc.subjectPaleoclimatologyen_AU
dc.subjectMeteoritesen_AU
dc.subjectOxygenen_AU
dc.subjectDendritesen_AU
dc.subjectCrystalsen_AU
dc.titleAncient micrometeorites suggestive of an oxygen-rich Archaean upper atmosphereen_AU
dc.typeJournal Articleen_AU
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