Goodyear dug four meters (13 feet) deeper than the soil layer containing the earliest North American people and began uncovering a plethora of tools.
Until recently, many archeologists did not dig below where Clovis artifacts were expected to be found.
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Since the 1930s, archaeologists generally believed North America was settled by hunters following large game over the land bridge about 13,000 years ago."That had been repeated so many times in textbooks and lectures it became part of the common lore," said Dennis Stanford, curator of archeology at the Smithsonian Institution.