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Proc Natl Acad Sci U S A. 2015 Apr 21;112(16):4859-64. doi: 10.1073/pnas.1405338111.

Changing the picture of Earth's earliest fossils (3.5-1.9 Ga) with new approaches and new discoveries.

Author information

1
Department of Earth Sciences, University of Oxford, Oxford OX1 3AN, United Kingdom;
2
Department of Zoology, University of Oxford, Oxford OX1 3PS, United Kingdom; School of Earth Sciences, University of Bristol, Bristol BS8 1RJ, United Kingdom;
3
Centre for Microscopy Characterisation and Analysis, The University of Western Australia, Crawley, WA 6009, Australia; and.
4
Centre for Microscopy Characterisation and Analysis, The University of Western Australia, Crawley, WA 6009, Australia; and Australian Research Council Centre of Excellence for Core to Crust Fluid Systems, The University of Western Australia, Crawley, WA 6009, Australia David.Wacey@bristol.ac.uk.

Abstract

New analytical approaches and discoveries are demanding fresh thinking about the early fossil record. The 1.88-Ga Gunflint chert provides an important benchmark for the analysis of early fossil preservation. High-resolution analysis of Gunflintia shows that microtaphonomy can help to resolve long-standing paleobiological questions. Novel 3D nanoscale reconstructions of the most ancient complex fossil Eosphaera reveal features hitherto unmatched in any crown-group microbe. While Eosphaera may preserve a symbiotic consortium, a stronger conclusion is that multicellular morphospace was differently occupied in the Paleoproterozoic. The 3.46-Ga Apex chert provides a test bed for claims of biogenicity of cell-like structures. Mapping plus focused ion beam milling combined with transmission electron microscopy data demonstrate that microfossil-like taxa, including species of Archaeoscillatoriopsis and Primaevifilum, are pseudofossils formed from vermiform phyllosilicate grains during hydrothermal alteration events. The 3.43-Ga Strelley Pool Formation shows that plausible early fossil candidates are turning up in unexpected environmental settings. Our data reveal how cellular clusters of unexpectedly large coccoids and tubular sheath-like envelopes were trapped between sand grains and entombed within coatings of dripstone beach-rock silica cement. These fossils come from Earth's earliest known intertidal to supratidal shoreline deposit, accumulated under aerated but oxygen poor conditions.

KEYWORDS:

astrobiology; biogeochemistry; early life; microfossils; paleontology

PMID:
25901305
PMCID:
PMC4413290
DOI:
10.1073/pnas.1405338111
[Indexed for MEDLINE]
Free PMC Article

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