ALLENDALE, S.C. -- Albert Goodyear breaks out in a drippy sweat each time he climbs into the rectangular pits lining the banks of the Savannah River.
"This place has kept me awake at night for a year," he confessed. "I just keep wanting to come back, to learn more."
Goodyear, director of the University of South Carolina's Institute of Archaeology & Anthropology, has studied countless relics during his 22-year career.
But none compare in significance to the hundreds of stone artifacts sifted during the past few months from Allendale County's prehistoric river clay.
For scholars of the past like Goodyear and his peers, the deeply buried fragments hint at troubling problems with the long-accepted theory of how and when the first humans populated the Americas.
Since the 1930s, scientists have believed the first humans in North America were from the Clovis culture, named for a site in New Mexico where stone spears -- some embedded in mastodon bones -- were unearthed.
The roving hunters were thought to have been Asians who trekked across a land bridge into Alaska and migrated south about 11,500 years ago.
Now that theory is unraveling.
Based on the artifacts found at the Allendale County dig, called the Topper Site, it now appears the human presence in the Americas is much older than anyone thought.
"What's at stake here is 75 years of archaeology that said there was nothing pre-Clovis," Goodyear said. "These could be the oldest artifacts found in North America."
The Topper site has been explored intermittently since 1983. But archaeologists just recently dug past the layers of known civilization into a mystery that could take decades to solve.
Near the surface were the common pottery shards and arrow points of the 1,000-yearold Mississippian cultures. Deeper down, researchers found artifacts from the Woodland and Archaic periods, dating back 4,000 years.
Culture after culture was unearthed as the layers of dirt were removed, culminating with the discovery of scrapers, tools and fluted blanks of stone consistent with the 11,500-year-old Clovis culture.
Beneath that Clovis layer was sterile clay -- the line where modern archaeology normally stops.
"Then there was several feet of nothing," Goodyear said. "But when we got a little bit deeper, these small, flaked tools started to appear."
The diggers had hit pay dirt in layers of soil far deeper -- and much older -- than anything explored during previous visits.
Although some finely notched points and other fancy artifacts were found at shallower levels, the important ones were little more than shapeless flakes of stone.
"It's not the kind of thing you'd make a tie tack out of," he said. "But it could change archaeology as we know it."
Unlike the skillfully carved tools of later cultures, the older artifacts were crude, simple "microblades" and scrapers.
"Whoever these people were, they didn't have access to big pieces of stone," he said. "They were on a completely different landscape."
Rather than shape large pieces of stone into arrow points or knives, Goodyear said, the early people attached multiple tiny blades to wooden sticks -- like a row of sharp teeth -- to form tools and weapons. …