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Oxygen-extinction theory draws counterfire.

It seems fitting that a team of researchers chose the week before Halloween to bring a controversial theory back for the dead. The scientists made news last week when they proposed that the dinosaurs died out because of a drop in the atmosphere's oxygen concentration 65 million years ago. Portions of that theory attracted intense criticism when first advanced six years ago, and researchers familiar with the work are showing even less charity this time around.

"It isn't cold fusion, but it has that kind of ring to it," says geochemist Harmon Craig of the Scripps Institution of Oceanography in La Jolla, Calif.

Gary P. Landis of the U.S. Geological Survey in Denver and his colleagues base their extinction theory on analyses of gas bubbles found in amber, a fossilized form of tree resin. They propose that the bubbles contain samples of air from the age of the dinosaurs.

At a meeting of the Geological Society of America in Boston, Landis and co-workers reported that the amber bubbles show a sharp drop in the atmosphere's oxygen concentration at the end of the Cretaceous period, from a high of 35 percent down to 29 percent. The researchers speculate that the oxygen decline -- caused by changes in volcanic activity and sea level -- killed off the dinosaurs because these reptiles had poor respiratory systems. This theory stands in contrast to the prevailing view that the dinosaurs and many other forms of life died out at the end of the Cretaceous at least in part because a huge asteroid or comet slammed into Earth.

Landis first raised the idea of analyzing air in amber in 1987 in a report with Robert A. Berner of Yale University. Landis and Berner came under attack from several scientists, who reported evidence that amber cannot trap air for millennia (SN:8/27/88, p.141). Berner has since disassociated himself from this research and has refused to comment on the new work.

Many researchers were surprised that the amber studies have continued. "I'm just absolutely mystified that it could get this far again," says Harold B. Hopfenberg, a chemical engineer at North Carolina State University at Raleigh.

Hopfenberg, who specializes in diffusion studies, reported in 1988 that results of an experiment with propane molecules showed amber to be relatively porous, with a diffusion coefficient for propane of [10.sup.-3] square centimeters per second ([cm.sup.2]/s). Because the main components of air are much smaller than propane, they should pass even faster through amber. Hopfenberg estimated that oxygen could premeate a chunk of amber within weeks, indicating that the gas trapped inside was hardly ancient air.

Craig and a colleague reached a similar conclusion in 1988, reporting that amber cannot contain air for long. Their experiments suggests that amber had a diffusion coefficient for oxygen of approximately [10.sup.-10] [cm.sup.2]/s, in line with Hopfenberg's findings.

Many researchers thought such results sealed the debate on amber's permeability. But Landis remains convinced that amber can trap air for millions of years. His own experiments with argon gas suggest that amber has a much lower diffusion coefficient, less than 1.5 x [10.sup.-18] [cm.sup.2]/s, he told SCIENCE NEWS. This figure is eight orders of magnitude smaller than that reported by Craig -- a disparity roughly equal to the difference between the length of a dollar bill and the diameter of Earth.

Hopfenberg takes issue with Landis' experiment: "He still confuses where, when, and how diffusional phenomena occur in amber." Craig says he too questions Landis' results. "You just don't have the feeling that is very believable," he says. If Landis and his colleagues cannot find stronger evidence to support their claims about amber, the scientific community may write off their dinosaur extinction theory as just hot air.
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Title Annotation:claim that dinosaurs died due to drop in atmosphere's oxygen concentration criticised
Author:Monastersky, Richard
Publication:Science News
Date:Nov 6, 1993
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