Sulfur-cycling fossil bacteria from the 1.8-Ga Duck Creek Formation provide promising evidence of evolution's null hypothesis

• Published in: Proceedings of the National Academy of Sciences - PNAS 2015-02, Vol.112 (7), p.2087-2092
• Main Authors: Schopf, J. William, Kudryavtsev, Anatoliy B., Walter, Malcolm R., Van Kranendonk, Martin J., Williford, Kenneth H., Kozdon, Reinhard, Valley, John W., Gallardo, Victor A., Espinoza, Carola, Flannery, David T.
• Format: Article
• Language: English
• Subjects: Bacteria; Bacteria - isolation & purification; Bacteria - metabolism; Biological Evolution; Biological Sciences; Evolution; Fossils; Fossils - microbiology; Hypotheses; Molecular biology; Morphology; Physical Sciences; Sulfur; Sulfur - metabolism
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1419241112

The recent discovery of a deep-water sulfur-cycling microbial biota in the ∼2.3-Ga Western Australian Turee Creek Group opened a new window to life's early history. We now report a second such subseafloor-inhabiting community from the Western Australian ∼1.8-Ga Duck Creek Formation. Permineralized in cherts formed during and soon after the 2.4- to 2.2-Ga “Great Oxidation Event,” these two biotas may evidence an opportunistic response to the mid-Precambrian increase of environmental oxygen that resulted in increased production of metabolically useable sulfate and nitrate. The marked similarity of microbial morphology, habitat, and organization of these fossil communities to their modern counterparts documents exceptionally slow (hypobradytelic) change that, if paralleled by their molecular biology, would evidence extreme evolutionary stasis. Significance An ancient deep-sea mud-inhabiting 1,800-million-year-old sulfur-cycling microbial community from Western Australia is essentially identical both to a fossil community 500 million years older and to modern microbial biotas discovered off the coast of South America in 2007. The fossils are interpreted to document the impact of the mid-Precambrian increase of atmospheric oxygen, a world-changing event that altered the history of life. Although the apparent 2-billion-year-long stasis of such sulfur-cycling ecosystems is consistent with the null hypothesis required of Darwinian evolution—if there is no change in the physical-biological environment of a well-adapted ecosystem, its biotic components should similarly remain unchanged—additional evidence will be needed to establish this aspect of evolutionary theory.