for National Geographic News
The long-gone land bridge between Asia and Alaska—a route possibly followed by the first humans to reach the Americas—flooded about 12,000 years ago, a new study suggests.
That's about a thousand years earlier than previously thought, adding to evidence that humans may have reached the Americas by other means.
"I think we're on the verge of rewriting the whole history of the region," said study leader Lloyd Keigwin of Woods Hole Oceanographic Institution in Massachusetts.
The new evidence from the Arctic also suggests that the thousand-mile-wide (1,609-kilometer-wide) bridge was available for a much shorter time than previously believed.
The commonly held theory is that humans migrated across the Pacific during the last ice age, which ended around 11,500 years ago.
During the Ice Age much of Earth's water was locked up in glaciers, resulting in lower sea levels that exposed land previously underwater. The land bridge north of the Bering Sea that once linked Siberia and Alaska, is one example (see an Alaska map including the Bering Sea).
As the Ice Age ended and glaciers melted, sea levels rose, eventually swamping the Bering land bridge—but when?
Keigwin's team collected data suggesting that the bridge flooded not 11,000 years ago, as is widely believed, but closer to 12,000 years ago.
The new results appear in the October issue of the journal Geology.
The report adds to a growing body of research that challenges the idea that the only route the Americas was a single land bridge from Asia around 12,000 years ago.
(Related: "Americas Settled by Two Groups of Early Humans, Study Says" [December 12, 2005].)
SOURCES AND RELATED WEB SITES