Critical testing of Earth's oldest putative fossil assemblage from the ∼3.5 Ga Apex chert, Chinaman Creek, Western Australia

The Apex chert 'microfossils' occur near the top of a 1.5-km long chert dyke complex associated with major synsedimentary growth faults. Highly localised, glassy felsic tuffs erupted explosively from this and other fissures during the early stages of volcanism, and were followed by the deposition of essentially hydrothermal black and white BaSO4 rich cherts that infiltrated the feeder dykes, underplating and dilating adjacent stratiform cherts before the start of the next volcanic cycle. The Apex chert 'microfossils' occur within multiple generations of these metalliferous hydrothermal vein cherts some 100 m down the dyke system. Comparable structures occur in associated volcanic vent glass and in hydrothermal cherts at least 1 km deep. We find no supporting evidence for a primary biological origin. We reinterpret the purported microfossil-like structures as pseudofossils that formed from the reorganization of carbonaceous matter, mainly during recrystallization from amorphous to spherulitic silica.