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Seminar Detail
A Whiff of Oxygen before the Great Oxidation Event
Presenter: Ariel Anbar ()
November 5, 2007 11:00 AM Pacific
Many lines of evidence point to a rapid rise of atmospheric O2 between 2.45 - 2.22 billion years ago (Ga), a transition often referred to as the Great Oxidation Event (GOE). The cause of the GOE is unknown. It could have been an immediate consequence of the evolution of oxygenic photosynthesis. Alternatively, O2 biogenesis may be ancient and the GOE a consequence of an abiotic shift in the balance of oxidants and reductants at the Earth’s surface that crossed a critical threshold at that time. In the latter case, oxygenic photosynthesis could have evolved long before the GOE. This debate can be addressed by looking for evidence of localized or short-lived concentrations of O2 before 2.45 Ga.
We have found evidence of low levels of O2 in the late Archean Mt. McRae Shale, Western Australia. Samples were obtained from a drill core recovered as part of the Deep Time Drilling Project of the Astrobiology Drilling Program. Analyses at high stratigraphic resolution across ca. 100 meters of this core reveal an episode of enrichment of the redox sensitive transition metals Mo and Re, as well as correlated changes in S isotope systematics. Re-Os geochronology demonstrates that the enrichment is a primary sedimentary feature dating to 2501 ± 8 Ma. Mo and Re were probably supplied to Archean oceans by oxidative weathering of crustal sulfide minerals. The changes in S isotopes indicate onset of oxidative S cycling. Together, these findings point to the presence of small amounts of O2 in the environment > 50 Ma before the start of the Great Oxidation Event.Participation Instructions
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The Director’s Seminar series features talks from scientists who are invited by the NAI Director to present their research results to the community. A primary goal of the seminars is to encourage interdisciplinary collaboration across NAI teams and within the astrobiology community at large.
Team Overview Seminars describe the work of the fourteen NAI teams and NAI Central. They offer an opportunity to find out more about the science, E/PO and other activities being performed by the NAI teams and the NAI Central office.
The Forum for Astrobiology Research (FAR) provides an opportunity for graduate students to present their research results and to meet as a student community for networking and mutual support.
The University of Washington seminar series is hosted by the NAI Virtual Planetary Lab (VPL) team from the UW campus in Seattle.
