A group of University scientists have proposed a controversial new theory about the end of the last ice age

For the record, they're not crazy.

But they do admit their theory is out there.

©Ryan Heidt
Two University researchers theorize that a comet may have hit North America about 13,000 years ago, causing an end to several species of animals near the end of the last ice age.


University researchers Douglas Kennett and Jon Erlandson are part of a group of scientists proposing that a comet or asteroid hit North America about 13,000 years ago - near the end of the last ice age - and contributed to major events in the continent's history, including the die-off of horses, mammoths and other large mammals around the same time.

The theory is turning decades of research on its head. The die-off of animals is usually explained by humans over-hunting the animals or an abrupt climate change.

"There are people who have made their whole careers on human hunters causing the extinction of animals," Erlandson said. "They've been writing about it for 40 years. There are some people who are not likely to be really happy with this theory."

Researchers say the comet - a ball of ice, rock and dust from outer space - hit the Laurentide ice sheet in Canada.

"It wouldn't have left a crater because it would have exploded and sent a shower of debris and chunks of ice," said Erlandson, adding the impact would have been ice on ice.

Heat from impact may have sparked fires across the continent, and the melting of the ice sheet may have caused flooding. Researchers say the comet may have contributed to human population reduction and localized animal extinction.

Researchers say the comet may have helped cause a cold climate period that lasted for about 1,300 years, called the Younger Dryas, and may have wiped out or fragmented the prehistoric Clovis tribe.

A carbon-rich black layer found at more than 50 sites around North America is evidence for the impact, according to the article published in the Proceedings of the National Academy of Sciences. The layer contains iridium, carbon spherules and fullerenes with helium 3. Evidence of mammoths and other animals, along with early human hunters, are found beneath the black mat, but are missing within or above the strip.

More evidence is found in the Carolina Bays, which are depressions from New Jersey to Florida. Erlandson says the depressions point toward the ice sheet, possibly a result of the comet.

The theory, which is known as the "YDB Comet Theory," was first proposed by University of California at Santa Barbara paleoceanographer James Kennett, Douglas Kennett's father, Richard Firestone of the Lawrence Berkeley National Laboratory and Arizona researcher Allen West. Douglas Kennett often collaborates with his father.

The theory has generated its share of naysayers.

University of Nevada at Reno anthropologist Gary Haynes says he and archeologist Stuart Fiedel object to the comet theory. In an e-mail, he listed reasons for the skepticism.

"In spite of what the comet theorists claim, Paleo-Indians thrive after the time of the supposed comet impact," Haynes said. "Clovis culture is transformed into Folsom, Dalton and Eastern U.S. variants, and all of these are much more numerous than Clovis, suggesting a human population increase, not collapse."

Graduate student Brendan Culleton, who is involved in the research, admits it's both scary and exciting to be involved in the studies.

"It's a crazy idea," Culleton said. "You should think this is insane when you hear about this."

Science and Nature magazines declined to publish the article.

"If the theory's true, it's the biggest story of the year - maybe the decade," Erlandson said.

Douglas Kennett, who is in Spain on sabbatical, said in an e-mail that there are and will be doubters.

"This is natural given the magnitude of this hypothesis and its potential significance in the history of our planet," Douglas Kennett said. "The scale of inquiry is also massive and we have just started to scratch the surface in terms of this event and its consequences."

Even the researchers themselves say the theory needs more work.

"I'm not 100 percent convinced, but there's tantalizing evidence," Erlandson said. "There's a lot more work that needs to be done to confirm this."

Erlandson said it could take a decade worth of research to prove the theory.

Douglas Kennett said the group needs to replicate some of its findings at existing localities with more refined techniques, and said they need to locate additional study sites both in the northern and southern hemispheres to determine if the effects are global beyond the effects of the Younger Dryas cold interval.

Erlandson said he will continue to have an open mind when it comes to the theory.

"Science moves on," he said. "You have to be driven by data."