Word: guidons
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...convincing fellow scientists has been a battle. Guidon's conclusions have been greeted with skepticism by many archaeologists. One problem, explains Randall White of New York University, is that the "tools" from the deepest levels at Pedra Furada are mixed with naturally fractured river gravel. This suggests that the geological layer was not laid down in an orderly way. The stone flakes could easily have been churned together with much older river rock before settling. Moreover, they might not be human-made at all; the artifacts themselves could have formed by natural erosion...
Critics have similar doubts about charcoal Guidon believes came from ancient fireplaces. "Radiocarbon dating is tried and true," explains archaeologist David Meltzer of Southern Methodist University. "The problem is linking the dating of objects to human occupation. How do you know it was a piece of charcoal touched by human hands and not just a piece of burned tree?" Brian Fagan of the University of California at Santa Barbara is a bit more blunt: "I think Pedra Furada is absolute horse manure...
That kind of derision doesn't faze the feisty Guidon. On the charcoal deposits, she argues, "If they had been left by forest fires, carbon deposits would have been found scattered across a wide area." They are not. In many cases, the charcoal is ringed by stones, says Guidon, which is strong supporting evidence that these were man-made hearths, not natural formations. Besides, the area was a humid, tropical rain forest 30,000 years ago, and natural fires would have had a hard time getting started...
...trouble her either. They couldn't have been washed in from elsewhere and mixed, she says, because the rock shelter where they were found is more than 60 ft. above the surrounding terrain. Nor < could the objects have tumbled down from higher up on the cliff, says Guidon, since the cave is protected by a massive rock overhang that would have kept out both falling rock and flowing water...
...thousands of years earlier. That would have been no problem, but heading south from there would have been tough: ice sheets -- or the inhospitable terrain they left behind -- cut off virtually all access to the bulk of North America from Alaska between 20,000 and 14,000 years ago. Guidon's rather controversial answer: maybe the immigrants came over to South America in boats directly from Asia...