At 251 Ma, more than ninety percent of marine species disappeared; land ecosystems were similarly devastated. Harvard team members seek to understand the causes and evolutionary consequences of this greatest of all mass extinctions. During the past year, D. Erwin and S. Bowring have continued field and laboratory research on the timing of P-Tr mass extinction, focusing on the earliest pulse of extinction and seeking to learn, through field study and radiometric dating of ash samples whether land and sea extinction occurred synchronously. J. Marshall and colleagues, including Co-I J. Grotzinger, continue to model end-Permian oceanographic conditions, helping to constrain scenarios for the largest known mass extinction. They have shown that if ocean circulation were weaker than it is now, consumption of oxygen could outstrip oxygen supply to the deep oceans, leading to anoxic deep waters rich in dissolved carbon. Were a rapid change in circulation to flush such a deep ocean, the rapid release of carbon dioxide to the atmosphere could have a significant impact on biology, perhaps triggering extinctions. Continuing research focuses on geological tests of model results, including expected carbon isotopic signatures.

Postdoctoral fellow K. Boyce and A. Knoll continued (with colleagues at Carnegie) to explore microchemical techniques that illuminate the physiology of fossilized organisms. They demonstrated that X-ray microspectroscopy allows detection of lignin-derived aromatic compounds in ancient tracheids and also showed that the conducting cells of early land plants were not lignified. Such microchemical techniques will be important when it comes time to analyze small samples returned from Mars.