The new research, published this week in Proceedings of the National Academy of Sciences, shows that structures once thought to be Earth’s oldest microfossils do not compare with younger fossil candidates but have, instead, the character of peculiarly shaped minerals. In 1993, US scientist Bill Schopf described tiny carbon-rich filaments within the 3.46 billion-year-old Apex chert (fine-grained sedimentary rock) from the Pilbara region of Western Australia, which he likened to certain forms of bacteria, including cyanobacteria.
The apparent find was controversial but the ensuing debate was hard to resolve until more advanced equipment became available, at which point:
Now Dr David Wacey, a Marie Curie Fellow in Bristol’s School of Earth Sciences, in collaboration with the late Professor Brasier, has come up with new high-spatial resolution data that clearly demonstrate that the ‘Apex chert microfossils’ comprise stacks of plate-like clay minerals arranged into branched and tapered worm-like chains. Carbon was then absorbed onto the edges of these minerals during the circulation of hydrothermal fluids, giving a false impression of carbon-rich cell-like walls.
So the new term is “pseudofossils.” And billions of years of long, slow Darwinian evolution apparently did not happen.
See Also: The Science Fictions series at your fingertips (origin of life)
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. [The article is available to the public as a .pdf. News] – Martin Brasier, Jonathan Antcliffe, Martin Saunders and David Wacey. Changing the picture of Earth’s earliest fossils (3.5-1.9 Ga) with new approaches and new discoveries. PNAS, 2015
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