Tom Dillehay is a controversial archaeologist as he was in charge of the excavations at Monte Verde in southern Chile. The controversy involved the dates for human activity he unearthed, unpopular at the time because Clovis First ruled the roost in North America. His dates, at the time, were 14,500 years ago, and humans had to get as far south as Monte Verde after the end of the Ice Age (around 15,000 years ago as far as melting ice was concerned). Dillehay, from Vanderbilts University in Nashville, has gone back to the site and after further excavations, getting lower, he has extended human activity in the region back to 18,500 years ago – which some people find quite unacceptable. See http://popular-archaeology.com/issue/fall-2015/article/new-clues-about-t… … and http://news.sciencemag.org/archaeology/2015/11/oldest-stone-tools-americ…
If Dillehay is correct it will shake up the lethargy around the peopling of the Americas. Geneticists claim the ancestors of the Palaeo Indians must have left Siberia no earlier than 23,000 years ago (www.sciencemag.org/content/349/6250/aab3884.abstract) which means they would require them reaching the tip of S America in an incredibly short period of time – and Dillehay is still working at Monte Verde (and the excavation is getting deeper).