<html>
<font size=6 color="#000080"><b><u>Earth System Initiative
Seminar<br><br>
</u></font><font size=5 color="#FF0000">Friday October 10, 12 Noon,
56-154 <br>
</font><font size=5 color="#800000">"Did Extinction at the
Precambrian-Cambrian Boundary lead to the Cambrian Radiation of
Animals?"<br>
</font><font size=5 color="#FF0000">Professor John Grotzinger<br>
</font><font size=4 color="#FF0000">Department of Earth Atmospheric and
Planetary Sciences, MIT <br><br>
</font>Biostratigraphic, carbon isotopic, and uranium-lead zircon
geochronological data from globally distributed regions indicate an
abrupt last appearance of Precambrian metazoans coincident with a
large-magnitude, but short-lived negative excursion in the
carbon-isotopic composition of seawater that is globally coincident with
the Precambrian-Cambrian boundary. U-Pb zircon age data from an
intercalated ash bed in Oman directly constrain this negative excursion
to be 542.0 Ma ± <0.5 Ma, consistent with previous constraints from
Siberia and Namibia. Combined with the global biostratigraphic record,
these new data strengthen hypotheses invoking mass extinction within
terminal Proterozoic ecosystems at or near the Precambrian-Cambrian
boundary.<br><br>
<br>
Pick up some lunch immediately before the seminar in 16-168.<br><br>
</b>Next Seminar:<br><br>
Thursday October 23, 12 Noon, 16-160.<br>
Joint ESI-CEE Distinguished Seminar Series<br>
Professor Edward DeLong<br>
Monterey Bay Aquarium Research Institute<br><br>
<br><br>
<x-sigsep><p></x-sigsep>
Matthew Gardner, Ph.D.<br>
Program Administrator<br>
Earth System Initiative, 16-177<br>
Massachusetts Institute of Technology<br>
Cambridge, MA, 02139<br>
617.253.6895<br>
<a href="http://web.mit.edu/esi" eudora="autourl">http://web.mit.edu/esi</a></html>