Christian Koeberl, Kenneth A. Farley, Bernhard Peucker-Ehrenbrink, Mark A. Sephton; Geochemistry of the end-Permian extinction event in Austria and Italy: No evidence for an extraterrestrial component. Geology 2004; 32 (12): 1053-1056. doi: 10.1130/G20907.1
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The end-Permian mass extinction (251 Ma) was the largest in Earth's history, and the great extent of biospheric perturbation is recorded as dramatic shifts in carbon isotope ratios of sedimentary materials. Both terrestrial and extraterrestrial events are commonly invoked as causative mechanisms for the crisis, and the primary reason for the event remains the subject of controversy. Geochemical indicators sensitive to the influence of extraterrestrial material involve platinum group elements and osmium and helium isotope ratios. Analyses of extinction levels in two sections from Austria and Italy reveal no evidence of an extraterrestrial impact. The end-Permian crisis, it appears, was a homegrown catastrophe.