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(Illustration by Andy Martin)

When Did Humans Come to the Americas?

Recent scientific findings date their arrival earlier than ever thought, sparking hot debate among archaeologists

Of the researchers working sites that seemed to precede Clovis people, Dillehay was singled out for special criticism. He was all but ostracized by Clovis advocates for years. When he was invited to meetings, speakers stood up to denounce Monte Verde. “It’s not fun when people write to your dean and try to get you fired,” he recalled. “And then your grad students try to get jobs and they can’t get jobs.”

The Monte Verde site gained wider acceptance after a panel of well-known archaeologists visited it in 1997 and reached a consensus. Dillehay was pleased that the panel had verified the integrity of his team’s work, “but it was a small group of people,” he said, meaning others in the profession continued to harbor doubts.

Two years later, an independent archaeologist, Stuart Fiedel, denounced Monte Verde’s authenticity in Scientific American Discovering Archaeology. Dillehay “fails to provide even the most basic” information about the locations of “key artifacts” at Monte Verde, Fiedel wrote. “Unless and until numerous discrepancies in the final report are convincingly clarified, this site should not be construed as conclusive proof of a pre-Clovis occupation in South America.”

The skepticism lingers. Gary Haynes, a University of Nevada-Reno anthropologist and a Clovis advocate, is not convinced. “There are only a few artifacts, and no flakes,” he said of Monte Verde, citing some of Fiedel’s arguments. “There are a lot of things that have been interpreted as artifacts but don’t look like them. Many of the things may not be the same age, because it is difficult to know exactly where they were found in the site.”

Dillehay rebuffs the criticisms: “More than 1,500 pages were published on Monte Verde, which is five times more than were ever written on any other site in the Americas, including Clovis. All of the artifacts came from the same surface covered by the peat bog and they all made sense in terms of the site’s activities. The vast majority are flaked pebble tools, typical of South American unifacial technologies. North Americans impose their evaluations on South America without even knowing the data down south.” He went on, “Now the field has moved on, and there are numerous pre-Clovis sites that have come to the forefront.”

***

At the Buttermilk Creek Complex archaeological site north of Austin, Texas, in a layer of earth beneath a known Clovis excavation, researchers led by Waters over the past several years found 15,528 pre-Clovis artifacts—most of them toolmaking chert flakes, but also 56 chert tools. Using optically stimulated luminescence, a technique that analyzes light energy trapped in sediment particles to identify the last time the soil was exposed to sunlight, they found that the oldest artifacts dated to 15,500 years ago—some 2,000 years older than Clovis. The work “confirms the emerging view that people occupied the Americas before Clovis,” the researchers concluded in Science in 2011. In Waters’ view, the people who made the oldest artifacts were experimenting with stone technology that, over time, may have developed further into Clovis-style tools.

Waters recently landed other blows to the Clovis orthodoxy in collaboration with Thomas Stafford, president of the Colorado-based Stafford Research Laboratories. In one series of experiments using accelerator mass spectrometry (AMS), a dating technique that is more precise than earlier radiocarbon measurements, they reanalyzed a mastodon rib from a skeleton previously recovered in Manis, Washington, and found to have a projectile point lodged in it. The original radiocarbon tests had surrounded the discovery in controversy because they showed it to be 13,800 years old—centuries older than Clovis. The new AMS tests confirmed that age estimate date, and DNA analysis showed that the projectile point was mastodon bone.

Deploying AMS technology, Waters and Stafford also retested many known Clovis samples from around the country, some collected decades earlier. The results, Waters said, “blew me away.” Instead of a culture spanning about 700 years, the analysis shrunk the Clovis window to 13,100 to 12,800 years ago. This new time frame required the Siberian hunters to negotiate the ice-free corridor, settle two continents and put the megafauna on the road to extinction within 300 years, an incredible feat. “Not possible,” Waters said. “You’ve got people in South America at the same time as Clovis, and the only way they could have gotten down there that fast is if they transported like ‘Star Trek.’ ”

But Haynes, of the University of Nevada-Reno, disagrees. “Think of a small number of very mobile people covering a lot of ground,” he suggests. “They could have been walking thousands of kilometers per year.”

Goebel, of the Texas A&M Center for the Study of the First Americans, characterizes his attitude toward pre-Clovis finds as “acceptance with reservation.” He said he’s disturbed by “nagging” shortcomings. Each of the older sites appears to be one-of-a-kind, he said, without a “demonstrated pattern across a region.” With Clovis, he adds, it is clear that the original sites were part of something bigger. The absence of a consistent pre-Clovis pattern “is one of the things that has hung up a lot of people, including myself.”

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