Letters to Nature

Nature 416, 76-81 (7 March 2002) | doi:10.1038/416076a; Received 14 February 2001; Accepted 24 January 2002

Questioning the evidence for Earth's oldest fossils

Martin D. Brasier1, Owen R. Green1, Andrew P. Jephcoat1, Annette K. Kleppe1, Martin J. Van Kranendonk2, John F. Lindsay3, Andrew Steele4 & Nathalie V. Grassineau5

  1. Earth Sciences Department, University of Oxford, Parks Road, Oxford OX1 3PR, UK
  2. Geological Survey of Western Australia, 100 Plain Street, East Perth, Western Australia, 6004, Australia
  3. Research School of Earth Sciences, Australian National University, Canberra ACT 0200, Australia
  4. School of Earth, Environmental and Physical Sciences, University of Portsmouth, Burnaby Road, Portsmouth PO1 3QL, UK
  5. Department of Geology, Royal Holloway University of London, Egham Hill, Surrey TW20 0EX, UK

Correspondence to: Martin D. Brasier1 Correspondence and requests for materials should be addressed to M.D.B. (e-mail: Email: martinb@earth.ox.ac.uk).

Structures resembling remarkably preserved bacterial and cyanobacterial microfossils from approx3,465-million-year-old Apex cherts of the Warrawoona Group in Western Australia1, 2, 3, 4 currently provide the oldest morphological evidence for life on Earth and have been taken to support an early beginning for oxygen-producing photosynthesis5. Eleven species of filamentous prokaryote, distinguished by shape and geometry, have been put forward as meeting the criteria required of authentic Archaean microfossils1, 2, 3, 4, 5, and contrast with other microfossils dismissed as either unreliable or unreproducible1, 3, 6, 7. These structures are nearly a billion years older than putative cyanobacterial biomarkers8, genomic arguments for cyanobacteria9, an oxygenic atmosphere10 and any comparably diverse suite of microfossils5. Here we report new research on the type and re-collected material, involving mapping, optical and electron microscopy, digital image analysis, micro-Raman spectroscopy and other geochemical techniques. We reinterpret the purported microfossil-like structure as secondary artefacts formed from amorphous graphite within multiple generations of metalliferous hydrothermal vein chert and volcanic glass. Although there is no support for primary biological morphology, a Fischer–Tropsch-type synthesis of carbon compounds and carbon isotopic fractionation is inferred for one of the oldest known hydrothermal systems on Earth.