THE WORLD'S GREATEST MIDLIFE CRISIS IN ANTARCTICA­THE PERMIAN-TRIASSIC EXTINCTIONS

 

Gregory J. Retallack, Department of Geological Sciences, University of Oregon, Eugene, OR 97403-1271; gregr ‘at’ uoregon.edu

 

The Permian-Triassic mass extinction is the largest known discontinuity in the history of life. New studies of superbly exposed sequences in Antarctica now demonstrate two separate but geologically abrupt mass extinctions on land. One mass extinction during the Middle Permian (260 Ma) extinguished as many species as the one that destroyed the dinosaurs at 65 Ma, and was followed by an even a bigger mass extinction during the Late Permian (253 Ma). Both Middle and Late Permian extinctions have long been apparent among marine invertebrates, and were also times of warm-wet greenhouse climatic transients, marked soil erosion, switch from high to low sinuosity and braided streams, soil stagnation in wetlands, and profound negative carbon isotope anomalies. Both mass extinctions may have resulted from catastrophic methane outbursts to the atmosphere from coal intruded by feeder dikes to flood basalts, such as the Middle Permian Emeishan Basalt and Late Permian Siberian Traps. These fatal greenhouse crises of the past are worst-case scenarios for greenhouse crises of the future.