2002 Annual Science Report
Harvard University Reporting | JUL 2001 – JUN 2002
The Planetary Context of Biological Evolution: Permo-Triassic Mass Extinction and Its Consequences
In this subproject, we seek to understand the causes and biological consequences of the great Permo-Triassic mass extinction, 251 million years ago.
During the past year, Erwin and Bowring have continued field and laboratory research on the nature, causes and timing of P-Tr mass extinction. Several descriptive papers were published on Permian and Triassic gastropods, and a model of recovery patterns was developed. Field work in China and South Africa is focusing on whether marine and terrestrial extinction pulses near the end of the Capitanian stage took place at the same time.
John Marshall and colleagues, including Co-I John 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 might outstrip oxygen supply to the deep oceans, leading to anoxic deep waters rich in dissolved carbon. Then, if a rapid change in circulation were to flush the deep ocean, bringing abyssal waters to the surface, the rapid release of carbon dioxide to the atmosphere could have a significant impact on biology, perhaps triggering extinctions. Current studies focus on the carbon isotopic signature expected for such a mechanism.
Postdoctoral fellow Kevin Boyce and A.H. Knoll completed work on late Paleozoic leaf evolution and continued (with colleagues at Carnegie) to explore microchemical techniques that provide insights into the physiology of early land plants. A paper demonstrating how X-ray microspectroscopy allows the detection of lignin-derived aromatic compounds in ancient tracheids has been followed up with a second paper showing that the conducting cells of early land plants were not lignified. Knoll also completed a paper with Richard Bambach quantifying the extent of change in marine community structure associated with end-Permian and end-Cretaceous mass extinctions.
PROJECT MEMBERS:Andrew Knoll
RELATED OBJECTIVES:Objective 5.0
Describe the sequences of causes and effects associated with the development of Earth's early biosphere and the global environment.
Define climatological and geological effects upon the limits of habitable zones around the Sun and other stars to help define the frequency of habitable planets in the universe.
Determine the resilience of local and global ecosystems through their response to natural and human-induced disturbances.