Pardee Keynote Symposia

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P6. Oxygen, Evolution, and Extinction

Sponsored by the Paleontological Society

Peter Ward, Robert Berner

Dragonfly size comparison A major discovery of the past three decades is that Phanerozoic oxygen levels fluctuated more than previously realized, and that major geological and evolutionary events probably were a consequence. For instance, times of low oxygen are associated with several mass extinctions, especially that at the Permian-Triassic boundary, while times of high oxygen during the Carboniferous and Permian allowed the evolution of giant insects and amphibians. Physiological experiments on modern organisms verify the association of elevated oxygen with increased growth rate. The high Permo-Carboniferous O2 levels were caused principally by the rise of vascular land plants and their greatly increased contribution to the global burial of organic matter in sediments. The conquest of land during the mid-Paleozoic, which took place in two parts, was also probably dictated by rising oxygen levels. Rates of evolution appear to be related to oxygen levels, with more "sluggish" evolution during times of high oxygen. Even the major make-up of animal body plans in the various phyla show that adaptations for respiration were a primary driver of anatomy. This session will present the latest findings on observations of the geological, paleobiological and geochemical record combined with physiological experiments on crucial organisms.

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