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"Extraordinary claims like this require extraordinary evidence, and we feel that the Cerutti Mastodon site [in San Diego] preserves such evidence," said Thomas Deméré, the study's corresponding author and curator of paleontology at the San Diego Natural History Museum. If confirmed, the new signs of human activity would be 100,000 years earlier than the “broadly accepted date for the first occupation of the Americas,” said researcher John McNabb of the University of Southhampton. Attempts in the 1990s to date the site suggested that the ivory was some 300,000 years old, but Deméré was sceptical: the method his colleagues used was problematic, and the age seemed so improbable for humans to be living in California.Over the past decade, archaeological research and studies of modern and ancient DNA have reached a consensus view on the peopling of the Americas : humans from Asia crossed the Bering land bridge into Alaska some 20,000 years ago and reached the southern tip of South America around 14,000 - 15,000 years agoSome archaeologists, however, maintain that humans arrived earlier. After several such experiments, it was clear that one of the only ways to produce the damage they saw on those 130,000-year-old mastodon limbs was to crush them with rock cobbles on rock anvils. The researchers behind the newly reported find came upon their evidence way back in 1992, when they made a routine check of a construction site for a noise-reducing berm near State Route 54 in San Diego. “They weren’t being transported by flowing water at the same time as the silt.” Instead, he suggests that they were carried to the site and used to infiltrate the mastodon bones—presumably to get at the marrow within. Using an excavator, scientists dug nearly 10 feet below the surface to uncover the remains, which neither geological forces nor human activity had disturbed in over 100,000 years, said Steve Holen, the study's lead author and director of research at the Center for American Paleolithic Research in South Dakota. Richard Potts of the Smithsonian Institution’s National Museum of Natural History, said he doesn’t reject the paper’s claims outright, but he finds the evidence “not yet solid.” For one thing, the dig turned up no basic stone cutting tools or evidence of butchery or the use of fire, as one might expect from Homo sapiens or our close evolutionary relatives. Probably, they conceded, these humans were a hybrid of several early humans, and possibly even a form of early Homo sapiens who roamed Asia more than 200,000 years ago. “If you are going to push human antiquity in the New World back more than 100,000 years in one fell swoop, you’ll have to do so with a far better archaeological case than this one,” he says.
A speculative study hypothesizes that a species of Homo may have lived in California 130,000 years ago.