"Where did the first DNA molecule come from? What kind of information did it carry (What for and where did it get it)? "
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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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1) You can listen to the seminar on the telephone while viewing the slides in WebEx (see WebEx instructions above). The NASA conference phone number will be displayed when joining the WebEx meeting.
2) You can watch the Realplayer webcast at: http://vanseg-1.arc.nasa.gov/2007/AB071105-01.ram and view the slides in WebEx (see WebEx instructions above) There is a 30 second delay for the webcast, so you will need to control the slides manually using the arrow buttons in WebEx. Questions for the speaker can be posted in the WebEx chat area to be answered at the end of the talk. Do not try to watch the Realplayer webcast at the same time as the Polycom or the phone.December 21, 2007
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