Dr. Janet L. Siefert of Rice University, and Dr. James F. Kasting of Pennsylvania State University have been awarded a grant from the Life in Extreme Environments (LExEn) program to trace past environmental crises in Earth history by using a combination of climate/biogeochemistry modeling and molecular systematic techniques. Models will help predict what kinds of organisms were capable of making the changes in atmosphere and to simulate interaction of different species ofmicroorganisms. For instance, initially archaea that produced methane might have dominated and then were usurped by bacteria that produced oxygen (cyanobacteria). Cyanobacteria are known to have existed by at least 2.7 Ga, so why does the rise in oxygen not occur for another 0.3 Ga? Their models will attempt to explain discrepancies such as this. Molecular systematic techniques will use DNA sequence data to track the ancestry of organisms and their genomes. These reconstructed ancestries will reveal which organisms were most likely present, whether there is evidence of 'molecular fossils' of new kinds of metabolism that may have evolved, and whether or not the assumptions of the climate/biogeochemical models make sense.