THE END-PERMIAN MASS EXTINCTION – A TEMPLATE FOR CO2-DRIVEN BIOTIC CRISES

Because the end-Permian mass extinction was the greatest biodiversity crisis of the Phanerozoic and a catalyst for the development of modern-style marine ecosystems, its causes have attracted a broader range of speculation than perhaps any other extinction. The proliferation of studies on the boundary interval in the past decade, drawing information from all fields of Earth science, has constrained potential extinction mechanisms and suggests that Siberian Traps volcanism was the primary trigger; resulting environmental degradation can account for most major features of the paleontological, sedimentary, and geochemical records. Large paleontological datasets show that the main pulse of extinction was geologically abrupt, perhaps shorter than 10 ka, and was coincident with the most intense phase of Siberian Traps volcanism. Metabolism and shell mineralogy are the traits that best explain survivorship patterns; genera with low metabolic rates and carbonate shells were more vulnerable to extinction stresses, consistent with physiological predictions under rising pCO₂ and resulting ocean acidification. The carbon isotope excursion, which began prior to the extinction, can be explained by massive injection of CO₂ derived from volcanic sources and volatilized organic carbon. Traps volcanism can also explain sedimentological and biomarker evidence for widespread ocean anoxia, which likely compounded the physiological stresses from elevated pCO₂. Carbon injection from volcanism would have enhanced weathering, increasing nutrient supply and exacerbating pre-existing ocean anoxia. Thus, the end-Permian extinction is one of the best-documented examples of a biotic crisis driven by physiological stresses of ocean acidification and hypoxia, and may provide a template for similar stresses during other ancient extinctions and during the 21st century and beyond.