Microfossils with tail-like structures in the 3.4 Gyr old Strelley Pool Formation Authors

International audience ; Some of the oldest traces for planktonic lifestyle have been reported in ca. 3.4 billion years old silicified sediments from the Strelley Pool Formation in Western Australia. Observation of flange appendages suggests that Archean life motility was passive and driven by drifting of microorganisms in their surrounding environment. Until now, the oldest traces for active motility are ca. 2.1 billion years old. Whether or not active motility already existed during the Archean eon remains an open question. In this study, we report the discovery of new 3.4 billion years old microfossils exhibiting a tail-like structure isolated from the Strelley Pool Formation. Exhibiting Raman spectra typically observed in organic-walled microfossils from the Strelley Pool Formation, these microfossils exhibiting a tail-like structure are syngenetic with their host rock. Composed of carbon, nitrogen, and, for one specimen, phosphorus, some of these organicwalled microfossils also exhibit significant level of aliphatic and amide moieties supporting their biogenicity. In addition, these microfossils exhibit a tail-like appendage sharing similar morphological features with locomotory organelles in modern microorganisms such as archaella, flagella, and cilia. This suggests that this observed appendage likely provided them with movement capabilities. If correct, with the ability to move, these microorganisms were capable of escaping from harsh environments and/or colonizing new ecological niches as early as 3.4 billion years ago.