People in Americas before last ice age?

People in Americas before last ice age?

A rock shelter on a sandstone cliff in northeastern Brazil has yielded evidence of the earlist known human occupation in the Americas, approximately 32,000 years ago, according to a report by two French scientists.

Although the discovery, reported in the June 19 NATURE, does not resolve long-standing arachaeological disputes over when and how people first arrived in the New World, the site is much older than others where human occupation has been firmly established. Several such finds in the southwestern United States date to 11,500 years ago, and a rock shelter near Pittsburgh is thought to contain evidence of use by humans 19,000 years ago; previously, the earliest known site occupied by humans in South America was 14,200 years old.

The case for a much earlier occupation at the Brazilian site, know as Pedra Furada, is based on radiocarbon dating of charcoal from hearths found in different layers of sediment beneath the floor of the shelter. Stone tools have also been found in the same layers of earth, say anthropologist Niede Guidon of the Institute of Advanced Social Science Studies in Paris and Georgette Delibrias of the French National Center for Scientific Research in Gif-sur-Yvette.

Carbon dates from the sedimentary layers indicate, according to the researchers, that the shelter was occupied repeatedly by different groups of tool-making people from at least 32,000 years ago until as recently as 6,000 years ago.

In addition, the investigators note that a hearth in the shelter dated at 17,000 years old contains a rock with two red painted lines, suggesting that cave art began in the Americas about the same time it appeared in Europe and Africa. The walls and ceiling of Pedra Furada are still covered with prehistoric paintings.

"Pedra Furada is a very important site," says anthropolist Alan L. Bryan of the University of Alberta in Edmonton. Bryan, who has visited the shelter, adds that the French carbon dating techniques are reliable and accurate.

"Some of the artifacts found by the French scientists appear to be manufactured by humans," says anthropologist Tom D. Dillehay of the University of Kentucky in Lexington, who recently observed the work at Pedra Furada. At a Chilean site, Dillehay has uncovered preliminary evidence of human occupation is sediments containing charcoal dated at about 33,000 years old.

Most archaeologists have held that people first reached the Americas from Asia sometime between 11,500 and 20,000 years ago by crossing a land bridge that connected Siberia and Alaska across the Bering Straits. At that time, the last ice age created massive continental glaciers and considerably lowered worldwide sea levels.

Recent South American discoveries that predate North American sites have caused some researchers to speculate that people first arrived in South America after voyaging across the Pacific Ocean and then spread northward.

Guidon and Delibrias do not, however, subscribed to this notion. "The present findings testify to the presence of man in the north of South America 32,000 years ago," they write, " and strongly suggest that the migration from Asia to North America occurred earlier."

Bryan agrees. "If you assume a Bering Straits entry, and I believe this to be a reasonable speculation, then there should be even earlier sites of human occupation in North America," he contends. He and his colleague Ruth Gruhn are now in Nevada looking for such sites.

A Bering Straits crossing 32,000 years ago is plausible, says Dillehay. "But we have to be cautious," he says. "You can't establish a theory of human origins in the Americas based on just one site."