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 News Articles Dying frogs sign of a biodiversity crisis Devastating declines of amphibian species around the world are a sign of a biodiversity disaster larger than just frogs, salamanders and their ilk, according to researchers from the University of California, Berkeley. Actions of individuals key to saving biodiversity-and ourselves, Stanford biologists say Even if you don't like the outdoors, you're probably pretty fond of air, clean water and food. That makes you a fan of biodiversity, because those essentials for life-human and otherwise-are maintained as a direct result of the Earth's biodiversity, the abundance and variety of species and populations on the planet. Preserving a substantial amount of biodiversity is critical to a healthy future for us, but how best to do that has been a subject of ongoing debate. New evidence implicates humans in prehistoric animal extinctions Research led by UK and Australian scientists sheds new light on the role that our ancestors played in the extinction of Australia's prehistoric animals. The study, published this week in the journal Proceedings of the National Academy of Sciences of the USA, provides the first evidence that Tasmania's giant kangaroos and marsupial 'rhinos' and 'leopards' were still roaming the island when humans first arrived. The Mystery of Mass Extinctions Is No Longer Murky If you are curious about Earth's periodic mass extinction events such as the sudden demise of the dinosaurs 65 million years ago, you might consider crashing asteroids and sky-darkening super volcanoes as culprits. Ebb and flow of the sea drives world's big extinction events If you are curious about Earth's periodic mass extinction events such as the sudden demise of the dinosaurs 65 million years ago, you might consider crashing asteroids and sky-darkening super volcanoes as culprits. New study reveals large scale conservation essential Scientists were surprised with findings of a recent study that reveals many animal species believed to persist in small contained areas actually need broad, landscape level conservation to survive. Geologists Discover New Way of Estimating Size and Frequency of Meteorite Impacts Scientists have developed a new way of determining the size and frequency of meteorites that have collided with Earth. Butterfly fish 'may face extinction' A beautiful black, white and yellow butterflyfish, much admired by eco-tourists, divers and aquarium keepers alike, may be at risk of extinction, scientists have warned. Seismic images show dinosaur-killing meteor made bigger splash The most detailed three-dimensional seismic images yet of the Chicxulub crater, a mostly submerged and buried impact crater on the Mexico coast, may modify a theory explaining the extinction of 70 percent of life on Earth 65 million years ago. Scientists warn that species extinction could reduce productivity of plants on Earth by half An international team of scientists has published a new analysis showing that as plant species around the world go extinct, natural habitats become less productive and contain fewer total plants -- a situation that could ultimately compromise important benefits that humans get from nature. More Mass Extinction News Articles |
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