3.46 Ga Apex chert 'microfossils' reinterpreted as mineral artefacts produced during phyllosilicate exfoliation

David Wacey, Martin Saunders, Charlie Kong, Alexander Brasier, Martin Brasier

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Abstract

Filamentous microstructures from the 3.46 billion year (Ga)-old Apex chert of Western Australia have been interpreted as remnants of Earth’s oldest cellular life, but their purported biological nature has been robustly questioned on numerous occasions. Despite recent claims to the contrary, the controversy
surrounding these famous microstructures remains unresolved.

Here we interrogate new material from the original ‘microfossil site’ using high spatial resolution electron microscopy to decode the detailed morphology and chemistry of the Apex filaments. Light microscopy shows that our newly discovered filaments are identical to the previously described ‘microfossil’ holotypes and paratypes. Scanning and transmission electron microscopy data
show that the filaments comprise chains of potassium- and barium-rich phyllosilicates, interleaved with carbon, minor quartz and iron oxides. Morphological features previously cited as evidence for cell compartments and dividing cells are shown to be carbon-coated stacks of phyllosilicate crystals. Three-dimensional filament reconstructions reveal non-rounded cross sections and examples of branching incompatible with a filamentous prokaryotic origin for these structures.

When examined at the nano-scale, the Apex filaments exhibit no biological morphology nor bear any resemblance to younger bona fide carbonaceous microfossils. Instead, available evidence indicates that the microstructures exfoliation of potassium mica flakes, plus the redistribution and adsorption of barium, iron and carbon within an active hydrothermal system.
Original languageEnglish
Pages (from-to)296-313
Number of pages18
JournalGondwana Research
Volume36
Early online date15 Aug 2015
DOIs
Publication statusPublished - Aug 2016

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Keywords

  • Apex Chert
  • Pilbara Craton
  • Microfossils
  • Pseudofossils
  • Archean life

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