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Project Progress

In the past year we have focused our investigations on the Late Ordovician glaciation and mass extinction in order to understand how global environmental perturbations affect the origin and evolution of complex life.

We have performed a series of global climate models for the Late Ordovician, wherein we varied paleogeography, pCO₂ levels, sea level, and ocean heat transport. We also used the output from the atmospheric general circulation model (AGCM) to drive a dynamic icesheet model. We found (Herrmann et al., submitted) that it is difficult to initiate glaciation with CO₂ values as low as 8 times present atmospheric levels (the lowest estimated values for the Late Ordovician) unless sea level and/or ocean heat transport are lowered. These results further constrain the necessary and sufficient conditions for glaciation in the Late Ordovician.

Based on our sample-standardized analysis of diversity through the Late Ordovician in Laurentia (Krug and Patzkowsky, 2001, 2002) we found that recovery of diversity in Laurentia following the Late Ordovician mass extinction may have taken place as much as 10 million years earlier than previously thought. Furthermore, the Late Ordovician mass extinction appears to have had a relatively small effect on the composition of the global biosphere, despite the fact that it is the second largest mass extinction known in the fossil record. This stands in stark contrast to both the Late Cretaceous and the Late Permian mass extinctions, which resulted in significant changes to the composition of the global biosphere. Significantly the Late Ordovician mass extinction is linked to a severe but short-lived glaciation (terrestrial cause), whereas the Late Cretaceous (and possibly the late Permian) is linked to an extraterrestrial cause. These observations suggest that the global ecosystem may respond differently, depending on whether environmental perturbations have terrestrial or extraterrestrial causes.