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Microbes eat carbon to live; it can be in the form of organic carbon, carbon
dioxide, or methane. Their metabolic processes fractionate 12C from
13C to varying degrees. These signatures can be preserved in the
rock record when carbonate precipitates contemporaneously with microbial
activity. However, numerous processes make these signatures difficult
to preserve and measure. By using computer modeling to predict the
size and distribution of isotopic shifts, insights into where and when
microbial shifts can be expected to be preserved in rocks. I have
started a modeling project to make these predictions, and am using the
results to guide sampling of ancient microbialites to identify these signatures.
The figure on the left shows the isotopic composition of total dissolved inorganic carbon above a 100 micron-thick photosynthetic mat located at 0 cm. Photosynthesis started at 0 hours. There is no convection in the overlying water, and the isotopic effects of the mat extend significantly into the water column. For a more complete explanation see my Microbial Influences... paper at the Astrobiology web site. |
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Dawn Y. Sumner
Department of Geology
University of California
Davis, CA 95616
dysumner@ucdavis.edu