ASSESSING POTENTIAL CLIMATIC IMPACTS ON THE EVOLUTION OF EARLY METAZOA

The snowball Earth glacial events of the Neoproterozoic Era and the subsequent transitions to non-glacial conditions undoubtedly placed enormous strain upon Earth's ecosystems. There has been considerable debate regarding the extent to which profound climate change may have spurred genetic mutations, leading ultimately to the proliferation of metazoan body plans during the Ediacaran revolution, and to the Cambrian explosion of the terminal Proterozoic and early Phanerozoic. Paleoclimate discussions of snowball Earth intervals have accordingly focused mainly upon the younger Varanger/Marinoan glaciations as potentially more relevant to metazoan evolution. However, given new time constraints that appear to shorten the interval between the Sturtian and Marinoan glaciations, and the fuzziness of molecular clock estimates for the divergence times of major taxa, it is possible that the Sturtian glaciation may have been influential as well.

Using a version of the NASA/GISS global climate model, we have run a series of simulations designed to compare surface environmental conditions for both the Sturtian and Marinoan snowball Earth glaciations. The simulations were altered to reflect the unique combination of boundary conditions for each glacial interval, including solar luminosity levels, continental distributions, and topographic estimates. The results of these simulations will be discussed in the context of the paleobiological record.