University Of Washington May 10, 2001 Collapse of simple life forms linked to mass extinction 200 million years ago A mass extinction about 200 million years ago, which destroyed at least half of the species on Earth, happened very quickly and is demonstrated in the fossil record by the collapse of one- celled organisms called protists, according to new research led by a University of Washington paleontologist. "Something suddenly killed off more than 50 percent of all species on Earth, and that led to the age of dinosaurs," said Peter Ward, a UW Earth and space sciences professor. Evidence indicates the massive die- off was linked with an abrupt drop in productivity, the rate at which inorganic carbon is turned into organic carbon through processes such as photosynthesis. The waning productivity coincided with a sharp decline in radiolaria (included among protists), which was the focus of the new research. One example of productivity, Ward explained, occurs in the spring when fertilizer washes into waterways and triggers large algae blooms. The processes at work in that scenario were reversed 200 million years ago, he said. There is no definitive evidence yet on what caused the demise of so many species, Ward said. However, the suddenness of the event is similar to two better-known mass extinctions - one 250 million years ago at the end of the Permian period that killed some 90 percent of all species, the other 65 million years ago at the end of the Cretaceous period that sent the dinosaurs into oblivion. The extinction 200 million years ago, at the boundary between the Triassic and Jurassic periods, killed the last of the mammal-like reptiles that once roamed the Earth and left mainly dinosaurs, Ward said. That extinction happened in less than 10,000 years, in the blink of an eye, geologically speaking. Ward is the lead author on a paper detailing the evidence, published in the May 11 edition of the journal Science. Others participating in the research are James Haggart and Howard Tipper of the Geological Survey of Canada in Vancouver, British Columbia; Elizabeth Carter, a researcher at Oregon's Portland State University; David Wilbur, a UW oceanography research scientist; and Tom Evans, a UW junior in chemistry and Earth and space sciences. The evidence from the extinction was gathered at two sites in the Queen Charlotte Islands, off Canada's British Columbia coast. "These sites are among the most remote places in the world," Ward said. "There are no roads anywhere close by. The forests are virgin old growth, and the wave action is such that you can't get there by boat." Samples from a spot called Kennecott Point, in the northern Queen Charlottes, and from Kunga Island, about 100 miles to the southeast, showed a sharp decline in the presence of organic carbon, even at places where levels of inorganic carbon rose. The organic carbon decline correlated with the decline of radiolarians, one- celled organisms that serve as a food source for a number of marine species. "These provide the best record of how nasty the extinction was at this boundary," Ward said. The mass extinction 200 million years ago occurred just before the breakup of Pangea, which contained all the land on Earth in one supercontinent. At the time, the Queen Charlotte Islands - which now lie between 52 and 54 degrees north latitude - were probably on the equator or in the southern hemisphere, Ward said. "These are tropical fossils. There are many kinds of fossils in these rocks," he said. And they tell a story of a calamity that came on with stunning swiftness. "This is the first time ever that we can see how sudden this event was," he said. "It was very quick, not a long protracted episode." Ward now has done research on the last three of the Earth's mass extinctions (scientists know of five) and has found that each happened quite quickly. Bolstered by a recent astrobiology grant from the National Aeronautics and Space Administration, he plans to lead researchers back to the Queen Charlottes this summer to look for more clues in the Triassic- Jurassic extinction, including potential causes.
By Robert Roy Britt Senior Science Writer, SPACE.com 11 May 2001 They call them the Big Five -- a handful of unfathomable mass extinctions over the past 500 million years, each estimated to have obliterated somewhere between 50 and 96 percent of all species on the planet. That much we know, because Earth recorded the mass deaths in layers of ancient soil, where crowds of miniscule corpses and other evidence show wholesale destruction of the smallest critters, on which larger animals depend. What we don't know, except in one case, is what caused these five mass extinctions. Nor is there solid evidence showing how rapidly the catastrophes occurred. Such knowledge would be a window not only to the past, but to the future: How likely is it that future Earth dwellers will meet with an inescapable catastrophic fate, much like the dinosaurs did? And how much time will there be to adjust or perish? While there are no firm answers, a three-page study in the May 11 issue of the journal Science adds modestly to a mounting stack of reports suggesting that asteroids and comets are the leading cause of terrestrial death, delivering immensely fatal blows every 100 million years or so that wipe the slate of life frighteningly close to clean in remarkably rapid fashion. Death came quick The new study involved the fifth largest known mass extinction, in which roughly half of all species were wiped out. It occurred about 200 million years ago at the boundary of the Triassic and Jurassic Periods in geologic history. This T-J boundary, as it is called, marks the dawn of the dinosaurs. In exposed soil layers on islands off the coast of British Columbia, researchers found that droves of marine plankton kicked their watery buckets at that time. Simultaneously, plants were disappearing rapidly, as seen in a quick drop in the rate at which organic carbon was created through processes such as photosynthesis. The extinction occurred in 50,000 years or less, the study's authors write, possibly within as few as 10,000 years - - the blink of an eye in geological terms. And far faster than previous estimates, which ranged up to 10 million years. The paper did not speculate about a cause. But Peter D. Ward, a University of Washington Earth and space sciences professor, and lead author of the study, told SPACE.com that the evidence makes it look very much like the later Cretaceous- Tertiary extinction, or K-T event, which wiped out the dinosaurs. The K- T event is the lone mass extinction for which researchers have a definitive smoking gun: A crater in the Yucatan Peninsula excavated by an asteroid. "The very rapidity of the [T-J] event and the geochemical and paleontological similarity to K-T boundary sections makes it look like an impact," Ward said. "My gut feeling is that it was impact." But he quickly added that there are other possible causes, such as rapid climate change due to heavy volcanic activity. The world's number-one killer? Noted University of Chicago paleontologist David Raup told SPACE.com that several studies have shown "reasonably good evidence" linking other mass extinctions to impacts, but these reports are "almost always ignored." Raup produced a study in 1992 suggesting that roughly 60 percent of all species extinction may have been caused by impacts. "I strongly suspect that in a few years this will be the conventional wisdom, but it is strangely slow in coming," Raup said. "Ward's paper and a couple of others recently on the Permian extinction may get people to rush to the other side of the boat." Other scientists agreed there remain other possible causes for Earth's greatest mass extinctions. But the case for cosmic impacts is growing. "It seems that several lines of evidence based on new data and careful statistical analysis are now showing that at least some of the great mass extinctions were geologically instantaneous, leading us to look for catastrophic causes such as asteroid impacts," said David Morrison, an asteroid researcher at NASA's Ames Research Center in California. "We know that impacts have occurred throughout Earth's history, so the connection seems plausible." Morrison cautioned that there is "much research yet to be done" before the connection can be made clear.
From CNN, 10 May 2001 By Richard Stenger (CNN) -- A cataclysmic event quickly killed off most of the species on Earth about 200 million years ago, after which dinosaurs began their long reign on the planet, according to a report to be published in Friday's edition of the journal Science. "This mass extinction has been known for a long time, but this is the first study to show that it happened suddenly," said paleontologist Peter Ward, lead author of the report. "This is the first time that we can see how sudden the event was. It was very quick. Not a long, protracted episode." Researchers found evidence of the rampant die-off, which took place on the boundary of the Triassic and Jurassic periods, by studying the fossil record of common marine plankton from the era. Between 50 and 80 percent of life on the planet didn't survive the catastrophic period, which lasted less than 10,000 years -- the blink of an eye in geological terms. Various causes suspected; dinos spared An asteroid collision, like those thought to have sparked other large- scale extinctions over the ages, is among the suspected causes of the episode. One such event 65 million years ago ended the age of dinosaurs. A sudden change in climate induced by a burst of volcanic activity may also have triggered the event. Ward and his colleagues noted that the die- off took place just before the breakup of Pangea, a supercontinent that included all the landmasses on Earth. Curiously, the extinction killed off mammal-like reptiles that once roamed the Earth, but spared the dinosaurs, according to the report. "Perhaps creatures reproducing with buried eggs survived and large animals with live births did not," Ward speculated. The researchers from the United States and Canada trudged through thick forests on remote islands off British Columbia to gather fossil evidence showing sharp, correlating collapses in organic carbon -- a marker of plant life productivity -- and radiolarians, single-cell organisms that served as a food source for many marine species. "These provide the best report of how nasty the extinction was at this boundary," Ward said. Copyright 2001, CNN |
