In The Field

ESA 2009: That ice age impact … not?

The always-controversial notion that a comet or asteroid slammed into North America some 13,000 years ago got a severe tongue-lashing today from a Wisconsin researcher. 2005an0816031-mammoth.jpg

The idea, put forth two years ago, suggests that an extraterrestrial impact somewhere over the Laurentide ice sheet abruptly terminated the last ice age and lead to the extinction of the continent’s great mammals, like mammoths (right), and some early peoples. A recent paper in Science proposes that physical evidence of the impact has been found in the form of nanodiamonds scattered across the continent. But both impact experts and paleoecologists have been reluctant to accept the idea.

Jacquelyn Gill, a graduate student at the University of Wisconsin in Madison, laid into what she called the “impact” (with quote marks heavy in her voice) today. Sediment cores at two locations in Indiana, and one in Ohio, are ideally located to preserve evidence of the environmental chaos such an impact would have caused. But no such traces are present, she reported at the meeting. In fact, declines in the abundance of a particular spore marker appears to take place more than 1,500 years before the purported impact would have happened, she says.

“We don’t see a real trend here that would suggest a physical impact,” she said.

Supporters of the impact idea have argued that no physical evidence of the impact itself — eg a crater — might be expected to remain. But evidence of massive environmental disturbance seems also remarkably slim, at least to researchers like Gill.

Image: Royal BC Museum, Victoria, Canada (where you can listen to a mammoth!)

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