title: Early Archaean microorganisms preferred elemental sulfur, not sulfate.
abstract: Microscopic sulfides with low 34S/32S ratios in marine sulfate deposits from the 3490-million-year old Dresser Formation, Australia, have been interpreted as evidence for the presence of early sulfate-reducing organisms on Earth. We show that these microscopic sulfides have a mass-independently fractionated sulfur isotopic anomaly (Delta33S) that differs from that of their host sulfate (barite). These microscopic sulfides could not have been produced by sulfate-reducing microbes, nor by abiologic processes that involve reduction of sulfate. Instead, we interpret the combined negative delta34S and positive Delta33S signature of these microscopic sulfides as evidence for the early existence of organisms that disproportionate elemental sulfur.
authors.affiliation: Equipe Géobiosphère Actuelle et Primitive, Institut de Physique du Globe de Paris, CNRS and Université Denis Diderot, 4 place Jussieu, 75005 Paris cedex, France. philippot@ipgp.jussieu.fr
authors.forename: Pascal
authors.initials: P
authors.lastname: Philippot
authors.forename: Mark
authors.initials: M
authors.lastname: Van Zuilen
authors.forename: Kevin
authors.initials: K
authors.lastname: Lepot
authors.forename: Christophe
authors.initials: C
authors.lastname: Thomazo
authors.forename: James
authors.initials: J
authors.lastname: Farquhar
authors.forename: Martin J
authors.initials: MJ
authors.lastname: Van Kranendonk
mesh_terms: D001315:Australia; D001466:Barium Sulfate / Q000737:chemistry; D003081:Cold Climate; D019015:Geologic Sediments / Q000737:chemistry* / Q000382:microbiology; D006862:Hydrogen Sulfide / Q000737:chemistry / Q000378:metabolism; D010084:Oxidation-Reduction; D013431:Sulfates / Q000737:chemistry / Q000378:metabolism; D013455:Sulfur / Q000032:analysis / Q000378:metabolism*; D013460:Sulfur Isotopes / Q000032:analysis; D016999:Sulfur-Reducing Bacteria / Q000378:metabolism*; D013696:Temperature
chemical_list: D013431:Sulfates; D013460:Sulfur Isotopes; D001466:Barium Sulfate; D013455:Sulfur; D006862:Hydrogen Sulfide