Posted on Friday 24 October 2003

An archaeological site in Siberia -- long thought to be the original jumping-off point for crossing the Bering land bridge into North America -- is actually much younger than previously believed, shaking the theory that the first Americans migrated overland during the final cold snap of the last great ice age.

Using radiocarbon dating, scientists found that the Ushki site, the remains of a community of hunters clustered around Ushki Lake in northeastern Russia, appears to be only about 13,000 years old -- 4,000 years younger than originally thought.

The new date places the Ushki settlement in the same time period as the Clovis site, an ancient community found in New Mexico, making it highly unlikely that people could have traversed the thousands of miles from Siberia in such a short period. "This was the last site out there in Siberia that could have been an ancestor for the Clovis," said Michael Waters, co-author of the research appearing today in the journal Science. "We have to think bigger now and start thinking outside the box."

[New questions about migration of first Americans]

The subject of when humans first arrived in America is hotly contested by academics.

On one side of the argument are researchers who claim America was first populated around 13,000 years ago, toward the end of the last Ice Age. On the other are those who propose a much earlier date for colonisation of the continent - possibly around 30,000-40,000 years ago.

The authors of the latest study reject the latter theory, proposing that humans entered America no earlier than 18,000 years ago.

[Date limit set on first Americans]