Researchers Rethink Dinosaur Die Off Scenario

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Model Used to Show Dust Dispersal

Pope used a model to show how the large dust particles found in the K-T layer [the geological term for the layer of Earth that dates to the time of the asteroid impact associated with the mass extinction] could disperse. From the results of his test he extrapolated how the finer dust particles, the ones that were supposed to have surrounded the Earth and altered its climate, would have dispersed.

He believes that the Yucatan impact could not have produced enough dust particles of a size that it would take to shut down photosynthesis for any significant length of time and therefore the original extinction theory is not valid.

Instead, Pope believes it may have been sulfur gases produced from impacted rocks and soot from global fires that shut down photosynthesis and caused global cooling.

The original studies of the clay layer found at the K-T boundary assumed much or all of this layer was derived from fine impact dust, he says. "More recent studies of this layer have shown this not to be the case. Furthermore, earlier estimates were based on extrapolations of data from surface atomic bomb blasts, which had about 100 million times less energy than the Chicxulub impact. Extrapolation over eight orders of magnitude is risky business. "

Pope, who was involved with the identification of the Chicxulub crater as the dinosaur killer in 1989-1990 when he worked at the NASA Ames Research Center, says that the current widely held theory suggests that the ash particles caused by the impact were so fine that they would have remained suspended in the air for a long time, making the Earth dark for an extended period.

But his model indicated that not enough ash could have been generated to do that. "In any event, the ash would not have dispersed in that way," Pope says. "Most of the ash would have fallen rather quickly near the impact area, causing substantial regional damage but having less effect with increased distance from the site," he says.

"The implication is that asteroids of a smaller size— with a diameter of under three kilometers— would not necessarily have the dire consequences for the planet that is currently believed," Pope says. "They would cause heavy regional damage, but the ash fall-out would not be as great as previously believed."

Pope says some scientists have challenged his theory. "They say there may be some other extinction mechanisms that smaller impacts trigger besides dust. That may be true, but no one has done the detailed studies to back up such arguments."

Recent National Geographic News stories on dinosaurs:
Researchers Melt Polar Dinosaur Mysteries
Scientist's Finds Spur New Thinking on Dino Evolution
Dino-Era Vomit Fossil Found in England
Study Paints New Picture of Dinosaur's Nose
Skeleton of New Dinosaur "Titan" Found in Madagascar
"Tidal Giant" Roamed Coastal Swamps of Ancient Africa
"Feathered" Fossil Bolsters Changing Image of Dinosaurs
Oddly Angled Teeth Make Masiakasaurus Stick Out

Additional dinosaur resources from National Geographic:
Paul Sereno: NG explorer-in-residence and dinosaur hunter
Wanted: Albertosaurus
Dinosaur Eggs
Destinations: Dinosaur National Monument

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