Nature advance online publication 7 February 2010 | doi:10.1038/nature08793; Received 12 June 2009; Accepted 15 December 2009; Published online 7 February 2010
Organic-walled microfossils in 3.2-billion-year-old shallow-marine siliciclastic deposits
Emmanuelle J. Javaux1, Craig P. Marshall2 & Andrey Bekker3
Department of Geology, University of Liège, 17 allée du 6 Août B18, Liège 4000, Belgium
Department of Geology, University of Kansas, 1475 Jayhawk Boulevard, Lawrence, Kansas 66044, USA
Department of Geological Sciences, University of Manitoba, 125 Dysart Road (Wallace Building), Winnipeg, Manitoba R3T 2N2, Canada
Correspondence to: Emmanuelle J. Javaux1 Correspondence and requests for materials should be addressed to E.J. (Email: ej.javaux@ulg.ac.be).
Although the notion of an early origin and diversification of life on Earth during the Archaean eon has received increasing support in geochemical, sedimentological and palaeontological evidence, ambiguities and controversies persist regarding the biogenicity and syngeneity of the record older than Late Archaean1, 2, 3. Non-biological processes are known to produce morphologies similar to some microfossils4, 5, and hydrothermal fluids have the potential to produce abiotic organic compounds with depleted carbon isotope values6, making it difficult to establish unambiguous traces of life. Here we report the discovery of a population of large (up to about 300 μm in diameter) carbonaceous spheroidal microstructures in Mesoarchaean shales and siltstones of the Moodies Group, South Africa, the Earth’s oldest siliciclastic alluvial to tidal-estuarine deposits7. These microstructures are interpreted as organic-walled microfossils on the basis of petrographic and geochemical evidence for their endogenicity and syngeneity, their carbonaceous composition, cellular morphology and ultrastructure, occurrence in populations, taphonomic features of soft wall deformation, and the geological context plausible for life, as well as a lack of abiotic explanation falsifying a biological origin. These are the oldest and largest Archaean organic-walled spheroidal microfossils reported so far. Our observations suggest that relatively large microorganisms cohabited with earlier reported benthic microbial mats8 in the photic zone of marginal marine siliciclastic environments 3.2 billion years ago.
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