Mass extinctions—moments in Earth’s history when a significant proportion of species become extinct over a short span of geologic time—are unusual. Paleontologists recognize only five such intervals of major dying in the Phanerozoic1, 2 (the last 542 million years of Earth’s history during which the fossil record is richest). There is debate among scientists both over whether these five mass extinction are truly exceptional3 and how many mass extinctions have occurred in Earth’s history.4 However, the fact that contemporary extinction rates are as much as 120,000 times higher than the normal or background rate5 qualifies the modern era as an episode of mass extinction potentially rivaling that at the end of the Cretaceous Period, when non-avian dinosaurs became extinct6-8. In our paper “Press-Pulse: A General Theory of Mass Extinction?” we concluded that the mass extinctions observed in Earth’s past required the coincidence of “press” (long term stress) and “pulse” (short term disturbance) events9. Yet if a combination of press and pulse mechanisms is required to generate a mass extinction, what accounts for the current biodiversity crisis? And how will understanding today’s presses and pulses help us to develop a better conservation policy?
The Press-Pulse Model of Mass Extinction


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