From the American Society for Microbiology… You know how we’ve been hearing for years that a huge impact probably wiped out the dinosaurs? Well, now it seems there is evidence to suggest that those silly scientists were off by a few hundred thousand years!
Gerta Keller of Princeton University claims that it was more likely a period of Global Warming that did the giant beasts in.
Microfossil Data Show Yucatan Impact Did Not Wipe out Dinosaurs
Recent microfossil evidence casts fresh doubt as to whether an asteroid wiped out the dinosaurs, according to micropaleontologist Gerta Keller of Princeton University in Princeton, N.J., and her collaborators. Their analysis of ancient marine-dwelling microorganisms, called foraminifera, suggests that global warming caused by massive volcanism in India Ã¢â‚¬Å“led to dwarfing of all species and a gradual decrease in their diversity beginning 400,000 years prior to the mass extinction,Ã¢â‚¬Â she says.
This analysis challenges a hypothesis formulated more than 25 years ago by geologist Walter Alvarez of the University of California, Berkeley, his father Luis, a physicist who had won the Nobel Prize, and their collaborators. They argued that a catastrophic cosmic event, often called the Chicxulub impact, on the northern Yucatan Peninsula of Mexico led to the demise of the dinosaurs. They traced that impact to the Cretaceous Tertiary (KT) boundary period 65.5 million years ago and claimed it caused extinction of 60% of all life on Earth from dinosaurs to microscopic marine organisms such as the foraminifera.
Ã¢â‚¬Å“We now have evidence that the Chicxulub impact occurred about 300,000 years before the end of the Cretaceous and thus didnÃ¢â‚¬â„¢t cause the mass extinction and, in fact, didnÃ¢â‚¬â„¢t cause any species to go extinct,Ã¢â‚¬Â Keller says, who presented her findings during the 2006 meeting of the Geological Society of America, held last October in Philadelphia, Pa. Thus, not only the foraminifera, but also amphibians, birds, insects, and dinosaurs apparently survived that impact. Paleontologists analyze the foraminifera to infer and decipher ancient oxygen levels, salinity, nutrient conditions, and sea level changes in the oceans. Moreover, because marine microorganisms are sensitive to environmental stress, the foraminifera are good indicators for extinction events since they were likely the first to succumb to damaging environmental changes.
Keller and her collaborators obtained drill core samples from Chicxulub sediments along the Brazos River in Falls County, Tex., the same region where other researchers believe that the KT impact generated tsunami deposits. Ã¢â‚¬Å“Our recent work shows that the KT boundary. . . is up to 1.0 meter above the top of those storm events,Ã¢â‚¬Â she says. Another 45Ã¢â‚¬â€œ60 cm lower lies Ã¢â‚¬Å“the original Chicxulub impact glass layer. . .Ã¢â‚¬Â Thus, these Brazos River core samples contain evidence of Ã¢â‚¬Å“three distinct events well separated in time and apparently unrelated.Ã¢â‚¬Â
Those drill core samples were crushed, analyzed, and examined for foraminifera. The findings suggest that global cooling led to a sea level drop from about 80 m to 30 m that apparently was more detrimental to foraminifera than was the Chicxulub impact, which occurred during the preceding warming. However, Keller says, it remains to be seen what really caused the mass extinction at the end of the Cretaceous period. It might have been another cosmic impact or the cumulative effects of rapid climatic and environmental changes.
Geologist Donald R. Prothero at the Occidental College in Los Angeles, Calif., is not surprised that new evidence leans away from the dinosaur impact extinction theory. Ã¢â‚¬Å“There is almost no further doubt among vertebrate paleontologists that birds are descended from dinosaurs,Ã¢â‚¬Â he says. Ã¢â‚¬Å“If that is the case, then dinosaurs did not die out at the end of the Cretaceous after all. . . . Dinosaurs [as birds] are all around you!Ã¢â‚¬Â