Rediscovering America
The New World may be 20,000 years older than experts thought
Scholarly rejection. Despite the primacy of the Clovis-first tale, some scientists never could quite embrace it. Over the years, hundreds of sites have been touted as older than the 11,200-year-old early Clovis sites, including Calico in San Bernardino County, Calif., endorsed in the 1960s by famed African anthropologist Louis Leakey as possibly more than 200,000 years old. But each time, at Calico and elsewhere, parades of outside experts said the "tools" were natural stones, or the dates were wrong, or supposedly human bones weren't human, or the charcoal was from a naturally caused wildfire, not a man-made hearth, or all that and more. The sites "have gotten their 15 minutes of fame, then disappeared into obscurity," said James Adovasio, professor of archaeology at Mercyhurst College in Erie, Pa.
Adovasio has his own tale of scholarly rejection. Since 1973 he has led excavation of the Meadowcroft Rockshelter, a 43-foot-high jutting cliff that provides protection from rain along its base. It looks out on Cross Creek, in rugged country 30 miles southwest of Pittsburgh. The landowner, Albert Miller, whose family has had the property since 1795 and operates a colonial-era museum there, called archaeologists in the early 1970s to investigate his hunch about Indian traces under the overhang. Miller's instincts were right. "Everybody and his brother stopped here," marvels Adovasio. Using razor blades to peel layers away, his crews have uncovered a rich trove of relics--20,000 stone tools, woven goods, nearly a million animal bones, and 300 fireplaces loaded with charcoal, making it easy for scientists to calculate dates. (Scientists estimate the age of charcoal and other organic material by measuring how much radioactive carbon-14 it contains. Living things absorb this isotope from the atmosphere; when they die, the radiocarbon begins to decay away. Although new studies suggest that solar variations throw the scale off slightly--11,000 radiocarbon years may be closer to 13,000 actual years, for instance--radiocarbon dating is still the gold standard for archaeological dating.) The cave was on a highway for traders, hunters, and migrants moving to and from the Ohio River Valley to the West. "If you were out camping and saw this place, this is where you'd stop, too," Adovasio says. Every accepted cultural period in Indian history and prehistory is represented: the contemporary Iroquoian Seneca; earlier and closely related "woodland" societies that reach back 1,000 years; the so-called archaic groups to around 8,500 years ago; and Paleo-Indians, including the Clovis big-game hunters, to about 11,000 years ago.
Trouble came when Adovasio began saying in the late 1970s that charcoal from human-made fire pits deep in the excavated floor of the shelter carried dates going back more than 14,000 years, with some indications approaching 17,000 years. He ran into what he calls the "Clovis curtain" of resistance. Critics told him the charcoal that he presumed came from wood may actually have been contaminated by ancient coal or carbon in the local sediments, which would carbon-date much earlier. Adovasio retorts that what he calls the "Clovis mafia" peculiarly rejects only dates at his site that are older than Clovis but not younger material. Contamination would skew ages for everything, he points out, not just for the finds that run counter to standard theory.
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