A stone knife and other artifacts found deep underwater in a Florida sinkhole show people lived in that area some 14,500 years ago. That makes the ancient sinkhole the earliest well-documented site for human presence in the southeastern U.S., and important for understanding the settling of the Americas, experts said. The findings confirm claims made more than a decade ago about the site. At that time, researchers reported evidence that humans were there some 14,400 years ago. But in an era when such an old date was widely considered impossible, other experts disputed the evidence, said Mike Waters of Texas A&M University. The sinkhole was just politely ignored," he said. Waters was among a new team of scientists who excavated there from 2012 to 2014. They report finding the knife and stone flakes in a paper released Friday by the journal Science Advances. The new work offers "far better" evidence for early humans than the earlier research did, he said. In American archaeology, sites showing signs of human presence more than about 13,000 years are called "pre-Clovis," since they predate the Clovis era of widespread human occupation. Dennis Stanford of the Smithsonian Institution's National Museum of Natural History said that he ranked the sinkhole with two locations in Pennsylvania and Virginia as "the best-dated and oldest pre-Clovis sites yet found in North America."