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Project Progress

Our current work focuses on the major environmental events recorded in the Phanerozoic carbon isotopic record, beginning at the Precambrian-Cambrian boundary 542 million years ago. Some of these events are associated with mass extinctions, and others are not. Recent work has concentrated on developing an understanding of this distinction.

We consider the size of environmental perturbations and the time scales over which they occur. Our work shows that the Phanerozoic perturbations of Earth’s carbon cycle exhibit a characteristic rate of change over two orders of magnitude in time scale. This characteristic rate is consistent with the maximum rate that limits quasistatic (i.e., near steady-state) evolution of the carbon cycle. We identify this rate with marginal stability, and show that mass extinctions occur on the fast, unstable side of the stability boundary. These results suggest that the great extinction events of the geologic past are associated with common mechanisms of instability. The root of this commonality likely lies in the microbial mediation of biogeochemical cycles.

In related work, we have performed a detailed study of the carbon isotopic event associated with the end-Permian extinction. This work led to the hypothesis that massive volcanism acted as a catalyst in the evolution of efficient acetoclastic methanogenesis, leading to a significant perturbation of the end-Permian carbon cycle. Some of the techniques developed in that study are now being used to analyze all Phanerozoic carbon-isotopic events.