Artifacts found in a hillside along the Savannah River indicate that modern humans inhabited North America as long as 50,000 years ago, a discovery that challenges long-held theories on the migration of our ancient ancestors.
The find reported Wednesday by archaeologist Albert Goodyear of the University of South Carolina flies in the face of the conventional scientific view that homo sapiens — with the same bone structure and brain size as today's people — moved into North America within the past 12,000 years. Until then, a 23,000-year-long Ice Age was thought to have blocked travel across Alaska's Bering Strait.

"Fifty thousand years ago is mind-boggling. It challenges a lot of theories," Archaeology magazine's Eric Powell says. "All of our models of how humans migrated will have to be reconsidered if this holds up," he says.

Goodyear and his colleagues have been exploring the ancient flint quarry in Allendale County, S.C., since 1998, unearthing a hearth, flint blades and tool chips.

The age estimate of the deepest artifacts is based on measures of radioactive carbon traces found in oak, conifer, buckeye and other plants buried alongside them.