INDUSTRY

By Karla Harby, NCSA -- During the late Permian period roughly 260 million years ago at least 90 percent of Earth's species vanished, never to be seen again. Researchers use Alliance resources to explore why. The single largest mass extinction of species that our planet has ever seen occurred not with the end of the Age of Dinosaurs, some 65 million years ago. Rather it occurred much earlier--toward the end of the Permian period, which spanned 286 to 245 million years ago and immediately preceded the beginning of the Age of the Dinosaurs. In the late Permian, most species, including perhaps 95 percent of all life in the oceans, simply ceased to be. Explanations for this mass extinction have been debated since it was discovered in the 1820s. In this respect, researching the Permian is much like researching the late Cretaceous, when the dinosaurs disappeared. But there's one big difference: 260 million years ago is a lot further away than a mere 65 million years. This dramatically affects the amount and kinds of evidence available to scientists studying the Permian mass extinction. "One of the interesting things about this is that the number of data points is very, very small," says John Marshall, an atmospheric scientist at the Massachusetts Institute of Technology. "Speculations are made from a few dozen data points, so there isn't much data to constrain the speculations." That's where Alliance resources come in. Using the Alliance SGI Origin2000 supercomputer at Boston University, Marshall and colleagues are building complex models of the Permian environment. While not full-blown simulations of the Permian world--there are simply too few data for that--these models allow the scientists to explore the feasibility of various extinction scenarios. That's because the models draw not only on the sparse geological record of the Permian, but also on oceanography, atmospheric science, paleobiology, and relevant chemistries. A few good rocks "Geologically, the further you go back, the less Earth you have to look at today," explains John P. Grotzinger, a geologist at MIT. Although entire mountain ranges date from the Permian--in western Texas, northern England, British Columbia, and Japan--much of this rock is not scientifically useful. To study such an ancient age, geologists need rocks that can be radiometrically dated based on the known rate of decay of uranium to lead; that contain fossilized animals or plants; or that provide specific information, usually trace elements that can be determined in ratios of one to another, about the nature of the paleoceanic environment. Because the Permian was so long ago, such data are subject to destruction and inaccessibility caused by more recent geologic events. What's more, to figure out what might have happened to so many marine species, "We need a much better understanding of how late Permian oceans may have worked. That's why John Marshall's work is so important," says Andrew Knoll, a Harvard University paleobotanist and expert on mass extinctions. "He's building on the kind of circulation models that have been constructed to understand circulation in today's deep oceans. That's no mean problem in itself." Unlimited speculations In stark contrast with today's oceans--where cold, highly oxygenated water is drawn to great depths--Marshall and colleagues theorize that during the Permian period, the deep ocean may have become stagnant and oxygen poor. Since nearly all life depends on oxygen, this would have created a lethal chemistry dramatically different from today's. It's an attractive explanation, but hardly the only one. In the past few months other research groups have reported evidence that volcanic activity altered the climate or that a devastating meteor hit the earth. "If it had been easy to settle, it would have been settled long ago," says Knoll, adding that there have been only two extinctions of this magnitude in the last 500 million years. "Because this event was so unusual, you can trot out unusual hypotheses to explain it." Given the paucity of observations, physical and biogeochemical models may offer the best way to constrain speculation. "It's best to build and study simple models first, and only then combine them together," Marshall notes. "What the Alliance computers help us do is to study the synthesis and connection between the component models in a comprehensive way." Stagnant depths The models Marshall and colleagues are studying begin with known characteristics of the physical world. For example, scientists know that the level of oxygenation of the deep ocean depends on the transport of oxygen-rich waters from the surface. But oceanic life consumes oxygen. Marshall's models suggest that if ocean circulation were weaker than it is now, consumption of oxygen might outstrip the supply of oxygen, leading to oxygen-poor (anoxic) deep oceans rich in dissolved organic carbon. Then, if a rapid change in ocean circulation were to flush the deep ocean--bringing abyssal waters to the surface--the rapid release of carbon dioxide to the atmosphere would have significant biological impacts, perhaps triggering extinctions. But what might cause the deep ocean waters to become stagnant in the first place? "We find through computer-based experimentation that the answer depends on the strength of the atmospheric hydrological cycle, the pole-equator temperature gradient, and the geographical distribution of land and sea, amongst many other things," Marshall says. Specifically, evidence suggests that by the end of the Permian period, the land masses of the Earth had aggregated into a single, hemispheric-scale supercontinent. Sea level was hundreds of meters below where it is today, the climate was warm and dry, and there were no polar ice caps. The scientists theorize, and simulate on the computer, that in this warm environment enhanced evaporation in the subtropics could have triggered haline convection, or the churning of seawaters caused by the increased density of water that comes with increased salinity. If this situation did occur, salt-heavy waters would have sunk to mid-depth, leaving the abyssal ocean stagnant, warm, and anoxic. But the models also show that the haline mode is unstable and eventually flips to a mode reminiscent of the present climate. In this thermal mode, cooling triggers deep-reaching convection at the poles, flushing the deep ocean with oxygen-rich water. This could explain how the ocean became life-friendly once again. Exactly when and how all this might have happened is under study. Currently the researchers are using their models to critically examine the conditions under which oceanic thermal and haline modes might be induced. "We find that, depending on the parameters, the ocean can remain for many thousands of years in one mode and then flip to the other mode," Marshall says. "The distribution of land and sea can favor one mode of circulation over another." So how close are scientists to agreement on the causes of the late Permian extinction? "A consensus is not going to occur easily or often," Knoll replies. "I'm not sure how close we are to solving it. But we know lots more than we did even 10 years ago." He adds, "It's predictive modeling like John's that's going to tell us what we should be looking for to answer these questions." This research is supported by the National Science Foundation. Relevant URLs: Access Online http://access.ncsa.uiuc.edu/CoverStories/permian/ For further information: http://paoc.mit.edu/paoc/research/warmclimates.asp http://puddle.mit.edu/~rong/permian.html