In a discovery sure to set off a firestorm of debate over human migration to the western hemisphere, archaeologists in South Carolina say they have uncovered evidence that people lived in eastern North America at least 50,000 years ago - far earlier than any previously known human presence.
If the results hold up, this could spur some significant rewriting of early human history. It adds to a growing body of evidence that human colonization of the Western Hemisphere is a more complicated - and much older - story than one involving simply a land bridge from Asia.
Cracks in that theory had already begun to appear in recent years. But the new evidence - in the form of stone tools buried deep in the South Carolina countryside - could be the most credible and provocative yet. Coupled with other finds, it promises to spur inquiry into the possibility the hemisphere's first humans may have come from Europe or Africa.
This could also put human migration to the Americas on the same time footing as human movement out of Africa and into Australia and Central Asia.
Lead archeologist Al Goodyear concedes that the findings of his group won't be accepted without debate. "I expect outright rejection of these results," he said in an interview. But he still asserts that the find is "the real deal."
The University of South Carolina archaeologist and his team uncovered what they interpret as simple stone tools in a layer of soil far below previous layers dated to about 16,000 years ago. "The geology and the [radiocarbon] dates are solid" for the layer in which the simple flake tools and coring tools were found.
The dating of the artifacts to some 50,000 years ago, announced at a press conference Wednesday at the university, comes at a period in North American archaeology when researchers are still smarting from bruising battles over evidence that humans arrived several thousand years earlier than the so-called Clovis culture, whose artifacts date to between 10,800 and 11,500 years ago.
"This is an interesting piece of information," says Tom Dillehay, an anthropologist at Vanderbilt University in Nashville. "It really needs to be compared against other available evidence. Even people with open minds will hesitate on 50,000 years."
Yet the South Carolina team's find is not alone in its antiquity - dates which begin to push the radiocarbon-dating techniques used to their limits. One site in Oklahoma has been dated to between 30,000 and 35,000 years ago. Brazilian and European archaeologists are working a site in Brazil that they say dates to 50,000 to 60,000 years ago. And a site in Chile has yielded artifacts dating to 33,000 years ago. In all cases, however, the evidence has been controversial.
Researchers interested in the origins of native Americans once held that the first Americans crossed a land bridge between Siberia and North America, then down into the "lower 48" through a corridor in the glaciers in the last ice age.
The idea evolved after unique spear points were discovered in Colorado and New Mexico, near Clovis in the 1930s. Once people knew what to look for, Clovis spear points began to appear throughout North America at what have been interpreted as quarries and kill sites where hunters had brought down their Pleistocene prey. Scientists applied radiocarbon dating techniques to organic material found in the same soil layers as the spear points and found them to be between 10,800 and 11,500 years old.
Yet several lines of argument and evidence have chipped away at the foundations of the Clovis culture as the earliest Americans, according Dr. Dillehay.
He notes that so far researchers have failed to find sites in Siberia with primitive hunting technologies similar to those of Clovis people. Only one or two Clovis habitation sites have been found, so little if anything is known about the culture's lifestyle. As with Goodyear's site, researchers have unearthed artifacts at eastern US sites that predate Clovis.
A Clovis-first approach fails to explain significantly older sites in Central and South America. And while genetic similarities between modern native Americans and Asiatic people have been documented, the high level of genetic diversity seen in native Americans "is difficult to explain in a Clovis time frame. It points to a deeper time."
These elements have undermined the Clovis-first theory sufficiently that now many researchers are open to the possibility that, like modern immigrants, people came at different times and from different parts of the globe - including Africa, Asia, Australia, and perhaps Europe. Indeed, most of the known Clovis sites are found in the eastern US. Some researchers have suggested that spear points found on the East Coast bear a striking resemblance to points found in Europe, raising the possibility that Stone Age Solutrean culture from what is now southwestern France may have made their way west.
"The vast majority of North American archaeologists have become convinced that Clovis doesn't explain the origins of the first people in the Americas," says Dr. Dillehay, whose work on a 13,000-year-old Monte Verde site in Chile was instrumental in turning the intellectual tide.
Goodyear and others agree a key point of contention will be whether the newly dated tools are human-made. Most Clovis-era tools, and even pre-Clovis artifacts, are worked on both sides of the rock. The Topper artifacts are flaked only on one side. Goodyear and others say that based on past experience, they are convinced that the artifacts were crafted with human hands. Critics are likely to view them as ambiguous, possibly nothing more than naturally chipped rocks.
In 1998, Goodyear dug below the level where Clovis artifacts were found and found odd stone tools up to 1 meter deeper. The soils in the layer were dated to 16,000 years ago. Last year, the team dug even deeper and found tools, as well as charred vegetation they could used for radiocarbon dating. The samples were recovered at the site and prepared by Tom Stafford of Stafford Laboratories in Boulder, Colo. The widely respected specialist then sent the samples to the University of California at Irvine for dating.
The resulting dates of up to 51,700 years old are minimum ages.