Researchers report biological affinities of the oldest known fossil microorganisms. The Apex chert formation from Western Australia is approximately 3.5 billion years old and contains some of the oldest known microbial fossils. J. William Schopf and colleagues used secondary ion mass spectroscopy to measure the carbon isotope composition of 11 Apex chert fossils representing five taxa. Each taxon had a characteristic carbon isotope composition that was similar to those of extant microbes, supporting the biogenic origin of these fossils. By comparing the isotope compositions of the fossils to those of extant microbes, the authors inferred the biological affinities of the fossil microbes. Two of the fossil taxa were inferred to be photosynthetic, one was inferred to be a methane-producing Archaean, and two were inferred to be methane consumers. The presence of methane-producing Archaea is consistent with phylogenies based on ribosomal RNA sequences, which suggest that such Archaea evolved early in the history of life. The results also suggest that methane cycling between methane-producing and methane-consuming organisms constituted a significant component of the early biosphere, according to the authors.
Article #17-18063: "SIMS analyses of the oldest known assemblage of microfossils document their taxon-correlated carbon isotope compositions," by J. William Schopf, Kouki Kitajima, Michael J. Spicuzza, Anatoliy B. Kudryavtsev, and John W. Valley.
MEDIA CONTACT: J. William Schopf, University of California, Los Angeles, CA; tel: 310-825-1170, 310-440-0510; e-mail: <firstname.lastname@example.org>