The best evidence yet for an early peopling of the Americas might lie at the bottom of a Florida river. That’s where a team of archaeologists has found ancient stone tools and butchered mastodon bones that have been reliably dated to 14,550 years ago—more than 1000 years before scientists once thought humans first reached the New World. The find, carefully excavated to ensure proper dating, helps shore up the early arrival hypothesis, which chiefly rests on only a few, often-contested sites in the Americas.
For most of the 20th century, archaeologists believed the first residents of the Americas arrived 13,200 years ago and belonged to the so-called Clovis culture, defined by their distinctive fluted stone tools. But in recent years, potentially older artifacts have turned up at a handful of sites, including Monte Verde in southern Chile and the Debra L. Friedkin site in central Texas, suggesting that people lived in the Americas long before the Clovis technology turned up. But few of these sites were free of issues; some lacked radiocarbon dates, whereas older and younger sediments appeared to be mixed together at others, casting doubt that tools found in pre-Clovis layers were actually made during that time. “It’s still a limited number of really good cases,” says Dan Sandweiss, an archaeologist at the University of Maine, Orono, who was not involved in the study. The Florida site, he says, “may be the best so far.”
The site, called Page-Ladson, was once an ambiguous case itself. In the 1990s, excavations there turned up a handful of stone tools and some mastodon bones that appeared to have been butchered. Radiocarbon-dating suggested the tools and bones were 14,400 years old, but the results weren’t conclusive, and many archaeologists remained unconvinced.
Page-Ladson “had always been on my hit list of sites to investigate,” says Michael Waters, an archaeologist at Texas A&M University, College Station, who has excavated several potentially pre-Clovis sites and is a co-author of the new study. The landscape around the site is made of limestone, pock-marked with numerous caves and sinkholes. Page-Ladson sits at the bottom of one of those holes. In pre-Clovis days, it would have looked like a small canyon with a small, marshy pond at the bottom. “This would have been a great place for humans to come and either attack and kill and butcher animals, or scavenge animals that had recently passed away at the bottom of the sink,” Waters explains. Thanks to changes in sea and groundwater levels, however, Page-Ladson is now totally submerged in the depths of the Aucilla River—and Waters doesn’t dive. So when he was offered the chance to reopen excavations at Page-Ladson, he recruited his former student, Florida State University in Tallahassee archaeologist Jessi Halligan, to lead the underwater expedition.
Halligan, already well-versed in the challenges of underwater archaeology, knew she had to be extra careful at Page-Ladson. Any inconsistencies could cast doubt on whatever pre-Clovis artifacts her team happened to find. So when one her team members uncovered an ancient stone tool called a biface, Halligan was ready. She and her team collected more than 70 samples of organic material around the tool, as well as the areas above and below it. It helped that the sediments contained “literal crap tons” of mastodon dung, a rich source of organic matter that was perfect for dating, she says. When they radiocarbon-dated the samples, they found that the biface was in a layer dated to 14,550 years ago, they report today in Science Advances. Crucially, their 70-plus dates fell in a nearly unbroken line from youngest at the top to oldest at the bottom, suggesting the sediments were not mixed up later. The excavation also revealed thin, unbroken strips of sediment dominated by shells; if the biface had drifted down from a younger layer, it is exceedingly unlikely those delicate sediments would have remained intact.
Over the course of two seasons, Halligan and Waters discovered butchered mastodon bones and a handful of other stone tools, though none as old or technically impressive as the biface. They also took the opportunity to analyze the sediments themselves, looking particularly at a specialized fungus that lives exclusively in the guts (and dung) of herbivores. For thousands of years, the sediments were full of that fungus, suggesting the presence of megafauna like mastodons. But at 12,600 years ago, all traces of that fungus vanishes—suggesting that the mastodons themselves may have disappeared from the region around that time.
Other archaeologists who study Paleoindians are impressed by the team’s rigor. When it comes to proving pre-Clovis occupation at a site, “the bar is still very high for me,” says Loren Davis, an archaeologist at Oregon State University, Corvallis, who wasn’t involved in the research. “I went into reading this [study] very critical.” But between the radiocardon dates and the painstaking stratigraphy, the researchers went above and beyond in proving that the biface is indeed 14,550 years old, Davis says. He adds that the study represents the “state of the art” for how first American sites should be studied, especially as more and more of those sites are likely to be found underwater. At the time people were present at Page-Ladson, ice sheets still covered much of North America, so the only way that people could have come to the Americas would have been by boat, hopping down the Pacific coast and then presumably using rivers to move inland. Sea levels were much lower then, so many of those sites are likely now submerged, Waters says. “I’m sure there are other Page-Ladson–like sites out there on the continental shelf just waiting to be found.”