SIXTY-TWO MILLION YEAR CYCLE IN BIODIVERSITY AND ASSOCIATED GEOLOGICAL PROCESSES

Recently, Rohde & Muller (Nature 2005) identified an unexpected 62 million year periodicity in the apparent biodiversity recorded in Sepkoski's Compendium of Fossil Marine Animal Genera. This was revealed in large part due to the recent improvements in the geologic time scale. This talk will review the evidence for that cycle, its relationship to extinction and origination, and recent discoveries pointing to geophysical processes associated with this periodicity. Among these discoveries are the observation of similar variations in the abundance of preserved geological sections (Smith & McGowan, Biology Letters 2005) and not yet published work showing correlated variations in large-scale volcanism and strontium geochemistry. This evidence, and the absence of any known astronomical process capable of generating the right periodicity, suggests that this cycle may have geodynamic origins. Specifically, a model is suggested such that a recurring thermal instability near the core-mantle boundary results in pulses of mantle plume formation. Such pulses would have important consequences for large scale volcanism, plate tectonics, geochemistry, and biology. If correct, these results suggest a new way in which geodynamical processes have been shaping Earth's environment and the evolution of life.