Archaeologists said yesterday they had found evidence that humans lived in North America at least 50,000 years ago, far earlier than has been thought.
The report was immediately met with skepticism by other scientists because the evidence had not gone through the usual process of review by independent researchers, which is especially crucial for something that would so dramatically rewrite human history. If humans migrated to the Western Hemisphere that early, it would force scientists to fundamentally rethink the early migration patterns of the species and the role of Homo sapiens so far back in this hemisphere.
But the researcher who led the team that made the discovery said he was confident the findings would hold up under scrutiny.
"It's really shocking -- we know that. Most archaeologists probably will reject this. We know we have our work cut out for us, to say the least," said Albert C. Goodyear, an archaeologist at the University of South Carolina. "But I believe it, so I have to call it as a I see it."
The findings are pieces of charcoal and shards of stone Goodyear and his colleagues unearthed at the Topper archaeological site along the Savannah River in Allendale County, S.C.
Modern humans are believed to have evolved in Africa between 60,000 and 80,000 years ago. Archaeologists have found evidence modern Homo sapiens migrated to Australia and central Asia about 50,000 years ago, and to Europe perhaps 10,000 years later.
But modern humans are believed to have migrated to the Western Hemisphere much later. For decades, the earliest signs of modern humans in the Western Hemisphere were believed to date back about only 13,000 years to a primitive culture known as Clovis, whose distinctive fluted projectile points have been found across the United States. Archaeologists have, however, begun to challenge the idea that the Clovis were the earliest human inhabitants in the area, citing findings that might push back that date back to about 20,000 years ago.
No one has previously said he has found any evidence that would push the date back 50,000 years.
In the new findings, Goodyear said his team dug down deeper than ever before at the Topper site and found tiny shards of flint that Goodyear believes are clearly the remains of ancient toolmaking. Then, the researchers found pieces of charcoal nearby in what could have been an ancient hearth, and sent the samples to the University of California at Irvine for radiocarbon dating, which is considered the gold standard for determining the age of archaeological artifacts.
The results, released yesterday, concluded the charcoal is at least 50,000 years old.
The researchers plan to submit the findings to a scientific journal for publication but decided to release the results before that because of intense media interest, Goodyear said.
Other scientists said they respected Goodyear's work but found it difficult to evaluate the findings without seeing details.
Although the date of the charcoal may be accurate, the pieces of stone found with it could easily have been created naturally instead of by ancient humans, Michael B. Collins of the University of Texas at Austin said.
"Nothing that I've seen is convincingly an artifact," Collins said. "I don't think the broken stones down there were broken by humans. I just don't see anything that makes me sit up and say, 'Wait a minute. Now he's got something.' "
David G. Anderson, an anthropologist at the University of Tennessee in Knoxville quoted the well-known scientific dictum that "extraordinary claims require extraordinary standards of evidence."
"Evidence of a human presence upwards of 40,000 years old in the New World has been proposed by many previous investigators, and none of these early claims survived careful professional examination," Anderson said.