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Four Theories about the American Population
* Clovis and the Ice Free Corridor
* Preclovis and the Pacific Coast Migration
* Solutrean Precursors to Clovis
* Trans-Pacific Contacts
One reason there is so much unsettled discussion has in part to do with the timing and character of the Last Glacial Maximum. The most widely accepted routes into the Americas come via the Bering Strait across what scientists call Bering Land Bridge. During the LGM, the routes into North America were blocked by glacial ice between at least 24,000 and maybe 30,000 and 18,000 years ago, at least so it seems, and yet there are archaeological sites that appear to have dates older than 18,000 years ago.
DNA and linguistic analysis have been brought to the discussion, but neither provides an unequivocal answer. One paper published by Perego et al. in January of 2009 suggests that Native Americans arrived in several waves into the Americas using two of these entry ways: the Ice Free Corridor and the Pacific Coast Migration model. The paper studied two mtDNA haplotypes and is well worth investigating.
It remains a puzzle.
The most widely accepted theory of the peopling of South America suggests that over a period of 3,000 years Paleoindians left Asia, crossed the Bering Strait on a land bridge that has since been submerged, then migrated through what is now the western United States and Central America into South America, settling along the Andes. Paleoindians in the Andes and those in North America had similar cultures, known as the Clovis tradition. These early hunters lived in open, temperate lands where they hunted large game with stone-pointed spears. The humid tropical forest environment of the Amazon was thought to have been too harsh for early people, and until now this area had not been investigated intensively by archaeologists.
"We now have hundreds of artifacts dated between 14,000 and 18,000 years ago," Goodyear says, standing deep in the pit from which he and an army of volunteers have been excavating them over the past several field seasons.
Then he points to a chert boulder and a streak of charcoal embedded in dun-colored clay six feet below him. Fragments were broken off the basketball-size boulder, he says, and used to make crude stone tools. The charcoal stain is, perhaps, an ancient hearth.
"Based on the radiocarbon dates of the charcoal, I think we have evidence of human activity here in the interior of America 40,000 to 50,000 years ago," he says. "It looks like people came here periodically to get chert for their tools. Where they came from and when, I still have no clue."