More Evidence Acquits Dino-Killer Meteor

By Larry O'Hanlon, Discovery News

March 27, 2006— The infamous dino-killer meteor was nothing of the sort, according to a story told by melted glass spheres ejected from the Yucatan's Chicxulub impact crater that landed as far away as Texas and Haiti.

The ages and chemical signatures of the glass spherules from northeast Mexico, Guatemala, Belize, Texas, and Haiti all indicate that the giant Chicxulub meteorite impact came 300,000 years too early to have been the culprit in one of the Earth's biggest mass extinction events 65 million years ago.

"The original spherule layer is not at the K-T boundary," said Chicxulub researcher Markus Harting of Utrecht University in the Netherlands.

By "original," he means the layer of spherules found in sediments from the various locations that mark the first fall of the spherules from the sky immediately after the impact.

Subsequent layers of "ejecta" spherules have been identified, but Harting's geochemical analysis shows they are all more worn and weathered, indicating that they are just re-worked spherules from the original layer.

Harting is scheduled to present his latest findings on April 3 at the co-meeting of the Geological Society of America and the Asociación Geológica Argentina in Mendoza, Argentina.

"He has the most comprehensive dataset on Chicxulub impact glass from the entire Central America area and now Texas," said geologist Gerta Keller of Princeton University.

(picture : This is a scanning electron microscope picture of an isolated, well preserved spherule from northeastern Mexico.)

She has studied some of the very same rocks to unravel the environments they represent. Her work also points to the Chicxulub impact being too early to account for the mass die-offs and the famous extraterrestrial iridium layer found worldwide in rocks at the Cretaceous-Tertiary (K-T) boundary, 65 million years ago.

The iridium layer is the original evidence used to argue for a mega-murderous impact.

"In essence, his work has confirmed that the oldest ejecta layer is the original Chicxulub fallout and that over time erosion, transport and re-deposition of the original spherule layer in shallow areas resulted in the additional spherule deposits," said Keller.

For those reluctant to abandon the killer meteor theory, Harting offers up the possibility that Chicxulub may have been in some way responsible for the extinction of ammonites, the once common nautilus-like sea creatures.

"Ammonites start to go extinct and are almost done before the K-T boundary," said Harting.

On the other hand, turtles and crocodiles weathered the K-T boundary just fine, which would seem to argue against the idea that the Chicxulub impact caused a worldwide dust storm that cooled and killed almost all life with a "nuclear winter" scenario. Turtles and crocs are warmth and sun-loving creatures, after all, he said.

And as for what, then, caused the famous iridium layer, which is undoubtedly from outer space, Harting said there are other possibilities.

One is that Earth and the entire solar system passed through a dense cloud of galactic dust 65 million years ago.

That would have caused harmless meteor showers that would have left their iridium in the atmosphere, and that would have been quickly rained out and deposited in lakes and oceans worldwide.

http://dsc.discovery.com/news/briefs/20060327/dinokiller_din.html

Soooo.. I guess we all are left with.. WHY did the dino's die? and where did the world wide iridium layer come from..???

Im not saying that they were not killed off from a different impact.. but... listening to the Discovery Science Channel Podcast (link found at right under radio links) 100 Greatest Discoveries - Evolution (Charles Darwin's theories radically changed the way we view the evolution of man. Other top discoveries in evolution include the Burgess Shale fossils that provide a snapshot of ancient life and the KT Asteroid which caused the demise of the dinosaurs.) made me think...

Once again the more we know .. the less we know we know :) - Az