New theory for mass extinctionsOctober 25, 2006A new theory on just what causes Earth's worst mass extinctions may help settle the endless scientific dust-up on the matter. Whether you favor meteor impacts, volcanic eruptions, cosmic rays, epidemics, or some other cause for the worst mass extinction events in Earth's history, no single cause has ever satisfied all scientists all the time for any extinction event. That may be because big extinctions aren't simple events. The new Press/Pulse theory gets around the controversy by rejecting the all-or-nothing approach to mass extinction, calling instead on a combination of deadly sudden catastrophes-"pulses"-with longer, steadier pressures on species-"presses." "What we wanted to do is move away from the idiosyncratic approach to extinction mechanisms and look for what these intervals had in common. If you have A and B you will get a mass extinction," said Ian West, a 2006 graduate of Hobart and William Smith Colleges in Geneva, NY. West and Hobart and William Colleges paleontology professor Nan Crystal Arens are scheduled to present their work on the Press/Pulse theory on Wednesday, 25 October, at the Annual Meeting of the Geological Society of America in Philadelphia. Using databases that chart genera of marine organisms and their extinctions through the fossil record, West and Arens divided the last 488 million years of geologic history into four groups: times of suspected impact events (Pulses), times of massive volcanic eruptions (Presses), times when neither Presses nor Pulses occurred, and times when Press and Pulse coincided. They compared average extinction rates in geologic stages in each of these groups. During stages when only impacts occurred, an average of 7.3% of genera became extinct every million years; 8.3% of genera became extinct in stages characterized by flood volcanism alone. When neither Press nor Pulse were active, 8.2% of genera became extinct. These averages are statistically indistinguishable. "Statistically speaking, extinction rates are not significantly higher at times of impact or volcanism vs. no geologic events," West said. In contrast, when Press and Pulse events coincided, an average of 12.8% of genera became extinct per million years, statistically higher than the rate observed during other geologic stages. "The goal of our work was to come up with a unifying theory of mass extinctions. We also wanted to make it applicable to what's going on now," said West, referring to rapid losses of biodiversity worldwide now underway as a result of climate change and destruction of habitats by human activities. "Is this model, which seems to work for the big five mass extinction events in Earth's history, applicable today?" West asked. At first glance the answer would appear to be 'no.' There is, after all, no massive flood basalt eruption underway today, nor have there been any recent meteor impacts. On the other hand, some very similar effects are being seen on Earth. "We came up with the idea that humans themselves act as both Press and a Pulse," said West. "Humans began manipulating the environment-the Press-from the advent of agriculture. However, that alone did not trigger the current mass extinction. That seems to have been triggered by the pulse of industrialization and the demands for energy and resources that came with it." The bottom line, says West is that it's extremely hard to pinpoint simple causes for Earth's great periods of extinction. "We sought to rephrase the question," said Arens. "In the modern world, species are commonly endangered by some stress before the final death blow falls. It seems likely that biological systems in the past worked in similar ways. By demonstrating that the coincidence of long-term stress and catastrophic disturbance is needed to produce big extinctions, we hope to break down some of the polarization characteristic of many discussions of extinction. We hope to send people back to the data with a more inclusive hypothesis to test." Geological Society of America |
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| Related Mass Extinction Current Events and Mass Extinction News Articles Conservation targets too small to stop extinction Conservation biologists are setting their minimum population size targets too low to prevent extinction. The first neotropical rainforest was home of the Titanoboa Smithsonian researchers working in Colombia's Cerrejón coal mine have unearthed the first megafossil evidence of a neotropical rainforest. A new day dawned fast In 1980, Luis Alvarez and his collaborators stunned the world with their discovery that an asteroid impact 65 million years ago probably killed off the dinosaurs and much of the the world's living organisms. But ever since, there has been an ongoing debate about how long it took for life to return to the devastated planet and for ecosystems to bounce back. Surviving mass extinction by leading a double life Drifting across the world's oceans are a group of unicellular marine microorganisms that are not only a crucial source of food for other marine life - but their fossils, which are found in abundance, provide scientists with an extraordinary record of climatic change and other major events in the history of the earth. Ancient volcanic eruptions caused global mass extinction A previously unknown giant volcanic eruption that led to global mass extinction 260million years ago has been uncovered by scientists at the University of Leeds. Princeton geoscientist offers new evidence that meteorite did not wipe out dinosaurs A Princeton University geoscientist who has stirred controversy with her studies challenging a popular theory that an asteroid wiped out the dinosaurs has compiled powerful new evidence asserting her position. New blow for dinosaur-killing asteroid theory The enduringly popular theory that the Chicxulub crater holds the clue to the demise of the dinosaurs, along with some 65 percent of all species 65 million years ago, is challenged in a paper to be published in the Journal of the Geological Society on April 27, 2009. New theory on largest known mass extinction in the history of the earth Did volatile halogenated gases from giant salt lakes at the end of the Permian Age lead to a mass extinction of species? Study unravels why certain fishes went extinct 65 million years ago Large size and a fast bite spelled doom for bony fishes during the last mass extinction 65 million years ago, according to a new study to be published March 31, 2009, in the Proceedings of the National Academy of Sciences. No joy in discoveries of new mammal species -- only a warning for humanity, Paul Ehrlich says In the era of global warming, when many scientists say we are experiencing a human-caused mass extinction to rival the one that killed off the dinosaurs, one might think that the discovery of a host of new species would be cause for joy. More Mass Extinction Current Events and Mass Extinction News Articles |
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