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<TITLE>CfA Colloquium: Andy Knoll/Mars/Th. Sept 8</TITLE>
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<P><A HREF="http://www.cfa.harvard.edu/cfa/calendar/latest.html"><U><FONT COLOR="#0000FF" SIZE=2 FACE="Arial">http://www.cfa.harvard.edu/cfa/calendar/latest.html</FONT></U></A>
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<P ALIGN=CENTER><FONT SIZE=2 FACE="Arial">Harvard Astronomy Colloquium</FONT></P>
<P ALIGN=CENTER><FONT SIZE=2 FACE="Arial">4 PM THURSDAY, SEPTEMBER 8</FONT></P>
<P ALIGN=CENTER><FONT SIZE=2 FACE="Arial">"Opportunity, Meridiani, and the Search for Life on Mars"</FONT></P>
<P ALIGN=CENTER><FONT SIZE=2 FACE="Arial">Prof. Andrew Knoll</FONT></P>
<P ALIGN=CENTER><FONT SIZE=2 FACE="Arial">Department of Earth and Planetary Sciences, Harvard.</FONT></P>
<P ALIGN=CENTER><FONT SIZE=2 FACE="Arial">Preceded by tea at 3:30 pm. Phillips Auditorium. </FONT></P>
<P><FONT SIZE=2 FACE="Arial">Abstract: The MER rover opportunity has carried out the first outcrop-scale investigation of ancient sedimentary rocks on Mars. The rocks, exposed in craters and along fissures in Meridiani Planum, are sandstones formed via the erosion and re-deposition of fine grained siliciclastics and evaporites derived from the chemical weathering of olivine basalts by acidic waters. A stratigraphic section more than seven meters thick measured in Endurance crater is dominated by eolian dune and sand sheet facies; the uppermost half meter, however, exhibits festoon cross lamination at a length scale that indicates subaqueous deposition, likely in a playa-like interdune setting. Silicates and sulfate minerals dominate outcrop geochemistry, but hematite and Fe3D3 (another ferric iron phase) make up as much as 11% of the rocks by weight. Jarosite in the outcrop matrix indicates precipitation at low pH. Cements, hematitic concretions, and crystal molds attest to a complex history of early diagenesis, mediated by ambient ground waters. The depositional and early diagenetic paleoenvironment at Meridiani was arid, acidic, and oxidizing, a characterization that places strong constraints on astrobiologial inference. </FONT></P>
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