Traces of some of South America’s earliest people found under ancient dirt pyramid

About 600 kilometers north of Lima, an imposing earthen mound looms over the sea. People began building the ceremonial structure, called Huaca Prieta, about 7800 years ago. But according to a new study, the true surprise lies buried deep beneath the 30-meter-tall mound: stone tools, animal bones, and plant remains left behind by some of the earliest known Americans nearly 15,000 years ago. That makes Huaca Prieta one of the oldest archaeological sites in the Americas and suggests that the region’s first migrants may have moved surprisingly slowly down the coast.

The evidence of early human occupation stunned Tom Dillehay, an archaeologist at Vanderbilt University in Nashville who led the new study. Initially, he was interested in examining the mound itself. But geologists on his team wanted to study the landform under the mound, so “we just kept going down,” he says. The deepest pit, which took 5 years to excavate, reached down 31 meters. Shockingly, those deep layers contained telltale signs of human occupation, Dillehay’s team reports today in Science Advances : evidence of hearth fires, animal bones, plant remains, and simple but unmistakable stone tools. Radiocarbon dates from charcoal place the earliest human occupation at nearly 15,000 years ago.

That’s made some researchers say Huaca Prieta should join the small but growing list of pre-14,000-year-old sites that have revolutionized scientists’ vision of the earliest Americans. Archaeologists used to think that people walked from Siberia through an ice-free passage down Alaska and Canada, reaching the interior of the United States about 13,000 years ago. In recent years, however, well documented earlier sites like Chile’s Monte Verde have convinced most archaeologists that humans made it deep into the Americas by 14,500 years ago, meaning that they would have had to cross Canada long before an ice-free corridor existed. That would have left them with one logical route into the Americas: down the Pacific coast. But direct evidence for such a migration is lacking.

The new find isn’t old enough to prove that the first Americans came down the coast, says Dillehay, who also excavated Monte Verde. But Huaca Prieta does provide a detailed snapshot of ancient coastal lives. The earliest residents lived in temporary camps in an ancient wetland, eating avocado, chiles, mollusks, sharks, birds, and sea lions. Interestingly, Dillehay did not find any fishing lines, nets, or harpoons. But he suspects people didn’t need them because storm surges would have sent seawater flooding deep inland, leaving behind pools full of stranded marine creatures. Then, the Huaca Prieta hunters could have simply smashed them over the heads and chowed down—much like people in the region do today, Dillehay says.

The Huaca Preita residents knew so much about their environment that Dillehay can’t imagine they were just stopping by on their journey south. If they were part of a wave of coastal migration, they certainly weren’t in a hurry. “This looks like people settling in,” agrees Loren Davis, an archaeologist at Oregon State University in Corvallis. “As old as this is, you’re probably not looking at the first peoples on the landscape.”

The Huaca Prietans managed to do all this with surprisingly simple stone tools. Instead of complex spear points, they used flakes knocked off round beach stones for everything from prying open shellfish to cutting up plants. “They’re like disposable razors,” says Matthew Des Lauriers, an archaeologist at California State University in Northridge, who has found the same kind of tools on Cedros Island off Baja California, where people lived more than 12,000 years ago. The similar tools could be evidence for the very first coastal migration, he says. But the only way to know for sure is to find more coastal sites.