Accidental find that could revolutionize North America Archeology "Jim Paces, a geochronologist at the U.S. Geological Survey in Denver, took dozens of slices from a rib and two femurs. Each slice, no wider than a millimeter, was dissolved in nitric acid. "The resulting solution contained trace amounts of uranium and thorium, which Paces extracted. After measuring those concentrates in a mass spectrometer, Paces concluded that the bones were 130,700 years old, plus or minus 9,400 years." "The conclusion seemed clear: Hominids, wandering through Southern California, had found a mastodon carcass and gone to work. They hauled cobblestones to the site...