We humans are newcomers to North America. Just how new is a point of bitter controversy among archaeologists. Work reported last month at the annual meeting of the Society for American Archaeology in Philadelphia has added fuel to the fire.
Like all good fights in science, this one involves new data that run counter to a cherished theory. The upstarts eagerly clamor for attention, while those holding the established view dismiss the new findings as inconclusive. After much shouting and disagreement, matters tend to sort themselves out, and a clearer picture emerges. This is how science is supposed to work, and it seems to be working very well in the field of American archaeology.
The traditional view of how humans first came to North America has been that they walked here from Asia. The last Pleistocene ice age reached its maximum 18,000 years ago, and as the ice began to melt, a land bridge became exposed across the Bering Strait, connecting Asia to Alaska. Walking over this narrow finger of land, and down the exposed west coast of Canada, ancient hunters could then have spread out into the interior of our continent.
Apparently, it took a while. The oldest widely-accepted evidence of Pleistocene humans in the New World is at Clovis, New Mexico. Radiocarbon dating tells us this Clovis site is about 11,500 years old. These early Americans produced a distinctive projectile point (arrowhead), very finely fluted and beautiful. Anyone who has ever seen a Clovis point would recognize another immediately. Although first found at Clovis, N.M., they are much more abundant in the east, especially the southeast United States. I have a Clovis point, given to me by my father, who found it in Georgia when he was a boy.
The traditional view, then, is that humans first arrived in North America about 12,000 years ago.
Two decades ago the upstarts began to challenge that view. Starting in 1977 an international team of archaeologists led by Tom Dillehay of the University of Kentucky began excavating a site in South America. The results, first reported in 1985, immediately caused an uproar. The Monte Verde site, adjacent to a small creek between the Andes and the Pacific in central Chile, was 12,500 years old! If its artifacts are really human, this site tells us that humans were in the New World more than a thousand years before Clovis.
Dillehay’s initial publication was met with sheer disbelief by most American archaeologists, but the longer they examined his mountain of carefully collected data, the more convincing it looked. A large team of scientists visited the Monte Verde site in 1997, and gave it their stamp of approval in a massive 1071-page report. Pre-Clovis New World humans were now officially recognized. Once the barn door was open, potential pre-Clovis sites began appearing like freckles on a sunny day. By far the most interesting of them is the one reported last month in Philadelphia. On a large sandy hill some 40 miles south of Richmond, Virginia, a team of researchers led by Joseph McAvoy has found evidence that humans camped at the site 18,000 years ago!
Called Cactus Hill after the prickly pear cactus that cover it, the site contains a wealth of evidence of ancient human presence. At one level there is a fine collection of classic Clovis points dating about 10,000 years ago. Below that is a layer of sterile sand about 6 inches deep. Digging further down in 1997, McAvoy found charred bones from an ancient campfire, and triangular projectile points that are clearly not like Clovis ones. Radiocarbon dating of the charcoal suggests that these artifacts are 8000 years older than the Clovis points above them.
McAvoy’s claim of 18,000-year-old Americans was met with a certain amount of skepticism, as any such claim should be. Perhaps the lower site was simply contaminated by the upper one, critics objected. Bits of carbon might have been moved down through the sand by plant or animal disturbances, for example.
To sort this out, McAvoy put together a team of 15 researchers and took a second, very detailed look. Scientists dated samples of the sand with a process called optically stimulated luminescence, which measures the time elapsed since grains were exposed to light. The layer of sand had indeed been covered for 18,000 years, backing up the radiocarbon date of the lower site. Importantly, there was virtually no vertical mixing of the sand. The lower site appears uncontaminated and undisturbed.
You can argue about the exact age of the lower site — maybe some carbon particles did sift down through the sand — but there is no getting around the fact that the ancient campfire McAvoy discovered deep within Cactus Hill south of Richmond is far below the Clovis site there, and thus certainly much older. The first American, it appears, was a Virginian.
George Johnson is a biology professor at Washington University, and a Virginian.
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