And although early studies arrived at some pretty errant dates, the technology has been refined and now, Bamforth notes, "it really works." But because the technology has only come into wide use in the past several years, many sites discovered and described earlier did not have the benefit of OLS dating.So if no biological material was available for handy radiocarbon dating, researchers would have had no way to gauge exactly when an assemblage of tools was made.This arrival would have placed the initial migration from northeastern Asia over the Bering Land Bridge and through the Arctic corridor that opened between ice sheets at some 15,000 years ago.This latest tool evidence, however, suggests that people were already making and discarding stone tools about 15,500 years ago, which would mean that the migration likely occurred even earlier.Researchers have also yet to find strong technological links between Clovis technology and same-period stone tools in northeastern Asia.
Douglas Bamforth, a professor of anthropology at the University of Colorado at Boulder who was not involved in the new research, calls the work "beautiful excavation and beautiful analysis." The Buttermilk Creek site is not the first evidence of pre-Clovis habitation of the Americas."You'd have to get to central Texas, and that would probably take a little while," Waters said.Waters argues that their find of 15,528 artifacts (made from chert, a flint-like rock), which span the 2,400 years before the accepted emergence of Clovis technology 13,100 years ago, is the nail in coffin of the theory that Clovis toolmakers were the first inhabitants of the New World, the so-called Clovis-first model."As you push it back," Bamforth says of the early settlement, "they have to come down the coast" before penetrating the continental interior.Recent descriptions of relatively sophisticated stone tools from California's Channel Islands also add strength to a costal path.The striking discovery of 14,100- to 14,600-year-old stone tools at a site in Monte Verde, Chile, raised questions about just how quickly the new settlers could have arrived so far south so quickly.These early people might have used the two continents' west coast as a pathway to settlement but, as Waters noted, it would mean those early explorers would have been "paddling as fast as they could to get down to the southern tip of South America," passing up a lot of awfully nice places on the North American coast along the way—such as the Columbia River, San Francisco Bay and San Diego, "where I would have stopped," Waters said, half jokingly."This is almost like a baseball bat to the side of the head to the archaeological community to wake up," he said.Uprooting the Clovis-first model Extracting and describing these thousands of small stone tools has been slow going.But the resources in the area were likely plentiful, added Michael Waters, of the Center for the Study of the First Americans at Texas A&M University in College Station and co-author of the new study.With the rich hill country around them, "it's not surprising people came back time and time again." The people who left the tools and fragments described in the study were likely hunter–gatherers, passing through the site from time to time over thousands of years.