title: Early evolution of large micro-organisms with cytological complexity revealed by microanalyses of 3.4 Ga organic-walled microfossils.
abstract: The Strelley Pool Formation (SPF) is widely distributed in the East Pilbara Terrane (EPT) of the Pilbara Craton, Western Australia, and represents a Paleoarchean shallow-water to subaerial environment. It was deposited ~3.4 billion years ago and displays well-documented carbonate stromatolites. Diverse putative microfossils (SPF microfossils) were recently reported from several localities in the East Strelley, Panorama, Warralong, and Goldsworthy greenstone belts. Thus, the SPF provides unparalleled opportunities to gain insights into a shallow-water to subaerial ecosystem on the early Earth. Our new micro- to nanoscale ultrastructural and microchemical studies of the SPF microfossils show that large (20-70 μm) lenticular organic-walled flanged microfossils retain their structural integrity, morphology, and chain-like arrangements after acid (HF-HCl) extraction (palynology). Scanning and transmitted electron microscopy of extracted microfossils revealed that the central lenticular body is either alveolar or hollow, and the wall is continuous with the surrounding smooth to reticulated discoidal flange. These features demonstrate the evolution of large micro-organisms able to form an acid-resistant recalcitrant envelope or cell wall with complex morphology and to form colonial chains in the Paleoarchean era. This study provides evidence of the evolution of very early and remarkable biological innovations, well before the presumed late emergence of complex cells.
authors.affiliation: Graduate School of Environmental Studies, Nagoya University, Nagoya, Japan.|Australian Centre for Astrobiology, University of New South Wales, Sydney, NSW, Australia.
authors.forename: K
authors.initials: K
authors.lastname: Sugitani
authors.affiliation: Graduate School of Environmental Studies, Nagoya University, Nagoya, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Mimura
authors.affiliation: Graduate School of Environmental Studies, Nagoya University, Nagoya, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Takeuchi
authors.affiliation: Laboratoire d'Océanologie et de Géosciences, Université de Lille, CNRS UMR8187, Villeneuve d'Ascq, France.
authors.forename: K
authors.initials: K
authors.lastname: Lepot
authors.affiliation: School of Informatics and Sciences, Nagoya University, Nagoya, Japan.
authors.forename: S
authors.initials: S
authors.lastname: Ito
authors.affiliation: Department of Geology, University of Liège, Liège, Belgium.
authors.forename: E J
authors.initials: EJ
authors.lastname: Javaux
mesh_terms: D005075:Biological Evolution; D005580:Fossils / Q000648:ultrastructure*; D019015:Geologic Sediments / Q000032:analysis*; D008855:Microscopy, Electron, Scanning; D046529:Microscopy, Electron, Transmission; D014904:Western Australia