Australia: The Land Where Time Began

A biography of the Australian continent 

Oldest Fossils that are Well-preserved

For some time the presence of sulphur metabolising microbes in the Early Archaean has been suggested  by sulphur isotope data from that time, resulting in proposals that for some time prior to 3.4 Ga the earliest microbial ecosystems may have been based on sulphur. Until the paper by David Wacey et al. published in Nature Geoscience, morphological evidence for these microbes was lacking². The microstructures reported by the authors were found in the Strelley Pool Formation, Western Australia, and were associated with micrometer-sized pyrite crystals. According to the authors, the microstructures exhibit indicators of biological affinity, such as hollow cell lumens, nitrogen enriched carbonaceous cell walls, taphonomic degradation, the cells formed chains and clusters, and δ¹³ C values that were about 33 % to about 46 % Vienna PeeDee Belemnite (VPDB). The authors of the paper identified them as spheroidal and ellipsoidal microfossils, as well as tubular sheaths that demonstrated the organisation of multiple cells. Based on the relevant properties of the associated pyrite crystals they were interpreted as by-products of the associated cells, indicating a metabolism by pathways utilising sulphur-reduction and sulphur-disproportionation. The microfossils have been dated to about 200 million years older than microfossils that had been reported previously from Palaeoarchaean siliclastic environments.

Microfossils dating to 3.5 Ga had previously been found at a nearby location by William Schopf, but the authors say the older structures are by-products of mineralisation.

Sources & Further reading

1. Cosmos Online
2. Microfossils of sulphur-metabolising cells in 3.4 billion year old rocks of Western Australia