2001 Annual Science Report
Harvard University Reporting | JUL 2000 – JUN 2001
The Planetary Context of Biological Evolution: Permo-Triassic Mass Extinction and Its Consequences
Permo-Triassic Mass Extinction and its Consequences (dm)
We have completed a lengthy review of the nature of the end-Permian mass extinction, including an evaluation of proposed extinction mechanisms. We seek to understand the causes and biological consequences of the great Permo-Triassic mass extinction, 251 million years ago. We continue to make progress along the lines outlined in our proposal. The additional of John Marshall as a Co-I has substantially improved our ability to frame and test hypotheses by oceanographic modeling.
We have been working on possible physical/biogeochemical mechanisms that may have been a player in the end-Permian mass extinction. This has involved developing circulation models of the paleo ocean and using them to drive biogeochemical models. Their focus has been the end Permian, but the insights and tools that have been developed are relevant to other warm periods of climate. This work goes a long way toward spelling out precisely what conditions are required to support a haline mode with sinking of brackish waters from the subtropics, a recurring scenario in the geological literature. Haline modes are favored in climates that are warm, with weak pole-equator temperature gradients, enhanced hydrological cycles and supercontinents.
Our recent work has sharply constrained the timing of end-Permian mass extinction. The event took place in a time interval shorter than (and perhaps much shorter than) 200,000 years. This result provides firm new constraints on the types of planetary or extraplanetary processes that could have caused this great extinction. Complementary research has clarified the nature of biological recovery following the extinction. It was the nature of the recovery and not just the particulars of the extinction that set the subsequent course of evolution on Earth.
In collaborative research, we modified standard electron microprobe techniques to make micrometer-scale elemental maps, including carbon, of silicified plants. These provide direct tests of taphonomic hypotheses regarding silica permineralization and demonstrate high-resolution, non-destructive microchemical assays of the type that will be criticial in the analysis of samples returned from Mars. We have also used NMR and soft X-ray techniques to examine the distribution of lignified tissues in early plants. This research shows that the anatomical modeling of tracheids was decoupled in time from lignification; more generally it paves the way toward physiological studies of ancient plants.
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.