Paleozoic mass extinctions: shared patterns suggest global cooling as a common cause.

Abstract

The three great mass extinctions of the Palaeozoic Era, those of the Late Ordovician, Late Devonian, and Late Permian epochs, shared a variety of features that suggest that climatic cooling was their primary cause. Each crisis was a protracted event in which tropical marine biotas, suffered major declines, and the reef community was decimated; as the Ordovician and Permian crises got underway, warm-adapted taxa were displaced toward the equator, and during the Devonian crisis, cool-adapted hyalosponges expanded in New York State while tropical taxa died out. Each crisis was followed by an interval characterized by cosmopolitan marine biotas and reduced carbonate deposition. Each mass extinction event approximately coincided with the initiation of a glacial interval at one of the three times during the Paleozoic Era when a major continent approached or passed over one of the Earth's poles. Climatic deterioration, probably resulting from plate movements, was the primary agent of all three mass extinctions. Late Ordovician cooling took place when Gondwanaland encroached on the South Pole, and an interval of continental glaciation was initiated. Late Devonian cooling may have resulted from: 1) a second encroachment of Gondwanaland on the South Pole, which triggered the Late Devonian glaciation now documented in South America, and 2) closure of the tropical seaway that had separated Gondwanaland from Laurussia. Late Permian cooling was associated with the formation of extensive glacial marine deposits on a northern terrane now attached to Siberia, while cold temperatures persisted in the south polar region, and a eustatic lowering of sea-level eliminated warm, shallow seas.-from Author