French researchers have found new evidence that man has lived in South America for at least 32,000 years, suggesting that Asians migrated across what is now the Bering Strait to the Americas more than twice as long ago as is currently believed.
The new report, published in today's issue of the British journal Nature, is the latest piece of evidence in what has often been an acrimonious scientific dispute about when the first settlers arrived on this continent. Previous studies suggested that Asians crossed the Bering Land Bridge more than 50,000 years ago, but all of those studies "have been discredited for technical and other reasons," according to UCLA anthropologist Gayle Kennedy.
"If (the French researchers) have solid evidence," Kennedy said, "this is a very important discovery."
Archeological sites normally are dated by analysis of charcoal and other carbon-containing artifacts. All living organisms incorporate radioactive carbon-14 into biological molecules. Scientists know how much carbon-14 is in an organism when it dies and how fast the carbon-14 is converted to non-radioactive forms.
By measuring how much carbon-14 is left in an artifact, therefore, it is possible to tell how long ago an organism lived or an artifact was made.
Currently, the oldest accepted site of human activity in the Americas is at Monte Verde in Chile, which dates back approximately 13,000 years. The oldest artifacts in California date from about 10,000 years ago, according to oceanographer Jeffrey L. Bada of the Scripps Institution of Oceanography.
Many scientists, such as anthropologist Christy G. Turner II of Arizona State University, believe that the oldest residents of this continent migrated from Asia roughly 15,000 years ago--about the time that glaciers were receding from the last Ice Age.
Subsequent waves of migration were thought to have occurred 6,000 and 4,000 years ago.
The new evidence, however, suggests that man immigrated here a much longer time ago and that small pockets of population persisted during the Ice Age.
Since 1973, French and Brazilian archeologists have been excavating an ancient rock shelter in Boqueirao da Pedro Furada, a plateau in the state of Piaui on the northeastern coast of Brazil. More than 200 similar caves decorated with wall paintings have been discovered on the plateau.
Anthropologist N. Guidon of the Graduate School of Social Sciences in Paris participated in excavations at the site and collected charcoal from four separate hearths that had been used intermittently by the prehistoric occupants of the cave. He also collected charcoal on small pieces of rock that had flaked off the wall paintings in the cave.
These charcoal samples were analyzed by G. Delibrias of the Center for National Research in Science at Gif-sur-Yvette, France. Guidon and Delibrias reported in Nature that the newest of the 17 charcoal samples they analyzed was about 6,000 years old and that the oldest was about 32,000. Fragments of charcoal from a wall painting were found to be 17,000 years old, which "makes the site of Pedra Furada the most ancient (painted cave) site in America, and one of the most ancient in the world."
Significantly, stone tools were found associated with each of the hearths, and the evolutionary refinement of the tools matches the historical sequence identified by radiocarbon dating.
Most anthropologists contacted by The Times were reluctant to draw conclusions about the new report because they had not yet seen it and because there have been so many previous reports that have turned out to be wrong.
"We just lost a date in the Yukon that looked very good for 27,000 years," UCLA's Kennedy said. "The scientists redid their dating and found that the new date was only a fraction of the old."
'Dates Haven't Held Up'
"In the past," said geologist Vance Haynes of the University of Arizona, "when it came down to critical examination of the evidence for older sites, the dates haven't held up. The possibility (that some of the sites are older) is there, but it's not something you want to pick up and run with."
If the French findings are confirmed, according to Bada, it will mean that man has been living in North America even longer. If the South Americans did migrate from Asia by way of the Bering Land Bridge, he said, they had to have passed through here first.