title: 3.4-Billion-year-old biogenic pyrites from Barberton, South Africa:  sulfur isotope evidence.
abstract: Laser ablation mass spectroscopy analyses of sulfur isotopic compositions of microscopic-sized grains of pyrite that formed about 3.4 billion years ago in the Barberton Greenstone Belt, South Africa, show that the pyrite formed by bacterial reduction of seawater sulfate. These data imply that by about 3.4 billion years ago sulfate-reducing bacteria had become active, the oceans were rich in sulfate, and the atmosphere contained appreciable amounts (>>10(-13) of the present atmospheric level) of free oxygen.
authors.affiliation: Department of Geosciences, The Pennsylvania State University, University Park 16802, USA.
authors.forename: H
authors.initials: H
authors.lastname: Ohmoto
authors.forename: T
authors.initials: T
authors.lastname: Kakegawa
authors.forename: D R
authors.initials: DR
authors.lastname: Lowe
mesh_terms: D019015:Geologic Sediments / Q000032:analysis*; D055593:Geological Phenomena; D005844:Geology; D006862:Hydrogen Sulfide / Q000032:analysis* / Q000378:metabolism; D007501:Iron / Q000032:analysis*; D009792:Oceans and Seas; D012623:Seawater / Q000032:analysis / Q000737:chemistry*; D013019:South Africa; D013431:Sulfates / Q000032:analysis* / Q000378:metabolism; D013440:Sulfides / Q000032:analysis*; D013460:Sulfur Isotopes; D016999:Sulfur-Reducing Bacteria / Q000378:metabolism
chemical_list: D013431:Sulfates; D013440:Sulfides; D013460:Sulfur Isotopes; C011342:pyrite; D007501:Iron; D006862:Hydrogen Sulfide