She also was able to show that the charcoal in the lower hearths was not produced by a forest fire. Soil scientist James C. Baker of Virginia Tech used a technique called luminescent dating to show that the sand at the site had not been disturbed over the millennia, suggesting that perturbation of the site by water or burrowing animals had not occurred. Others were able to demonstrate the presence of distinctive plant fossils, called phytoliths, produced when plants on the surface are damaged, as by human activity. The amounts of phytoliths spiked at the levels of the campsites. The team also found high levels of phosphates in the soil at the levels of the sites.
Phosphates are the detritus of human wastes and garbage.
The Smithsonian's Stanford, however, thinks the tools are remarkably similar to somewhat older tools recently discovered in Spain and France. He suggests that those proto-Spaniards might have sailed across the Atlantic 18,000 years ago or more. Not everyone is convinced. Archaeologist David Meltzer of Southern Methodist University questions the fact that the two campsites discovered at Cactus Hill, separated in time by several thousand years, are separated in space by only 7-10 cm.