Joe Kirschvink's Talk Friday

Not to be missed!

Our IGPP Seminar series for Winter Quarter 2005 continues this Friday, January 14, 2005.  The seminar is sponsored by CODEP.

Speaker/Affiliation:

Joe Kirschvink
Caltech

Seminar Title:


"A Paleoproterozoic Planetary Suicide Attempt: Did The Evolution of Oxygenic Photosynthesis trigger the first Snowball Earth?"

Abstract:

The rise of oxygenic photosynthesis and the oxygenation of the atmosphere are two of the most important events in Earth history. A preponderance of evidence now supports the hypothesis that planetary oxygenation occurred between 2500 Ma and 2200 Ma. While biomarker evidence has been used to claim that oxygenic photosynthesis evolved several hundred million years before the oxygenation event, doubts remain about both possible sample contamination and the reliability with which biomarkers can be tied to oxygen-demanding pathways. Moreover, the co-incidence of planetary oxygenation with the Paleoproterozoic Snowball Earth suggests an alternative history, in which the evolution of oxygenic photosynthesis triggered the geologically rapid destruction of a methane greenhouse and a Snowball Earth event. We propose a new correlation between the Huronian Supergroup, Canada, and the upper Transvaal Supergroup, South Africa, in which the three Huronian glaciations predate the oxygenation event while the Paleoproterozoic Snowball Earth was triggered by it. A simple computational model of C, Fe, and P fluxes during the oxygenation event suggests that, under a range of plausible fluxes, cyanobacteria could have destroyed a methane greenhouse and triggered the Paleoproterozoic Snowball Earth on timescales as short as 1 myr. The geologic record currently permits multiple testable hypotheses about planetary oxygenation and all deserve critical consideration.

Host:
Don Korycansky

When:
Friday, January 14, 2005 at 3:30 P.M.

Where:
Natural Sciences Annex, Room 101

Refreshments will be provided in the E&MS Dreiss Lobby at 3 P.M.  Please Join Us.