For decades, archaeologists have concluded that the first humans entered the Americas over the Bering Straits land bridge about 13,000 years ago, when an ice-free corridor opened up in Canada, But in 1976, a discovery was made in Chile which forced that conclusion to be re-written.
Replica Clovis point.
In 1976, American archaeologist Thomas Dillehay was teaching courses at The Southern University of Chile when a student brought in some fossils to show him. They were mastodon bones, including a tooth, that had been accidentally uncovered while some local farmers were clearing a road for their ox-carts. Examining the find, Dillehay was intrigued when he found marks on the bones that seemed to have been cutmarks, made when stone tools were used to cut the joints apart and strip off the flesh. Since ancient hunting sites were rare in South America (most jungle soils are wet and acid, which is not conducive to preserving bones), Dillehay decided to check it out, and the next year, he took a small team to the site, within a shallow bog at a place called Monte Verde, and began excavating.
What they found was interesting: more mammoth bones with cut marks, but also stone flake tools and clay hearths containing charcoal and the remnants of burned plants. Apparently it was an ancient campsite.
What made it particularly interesting was the age of the site. The earliest-known examples of humans in the western hemisphere were called “Clovis”, after the site in New Mexico where their distinctive fluted stone points were first found. From genetic and linguistic evidence, anthropologists knew that the Native American peoples in North and South America were descended from Asian people who lived in Siberia, and who likely crossed over the land bridge, called Beringia, that once connected Russia to Alaska. And from geological evidence, scientists knew that this pathway was blocked during the last Ice Age by thick glacial ice about 22,000 years ago, and stayed blocked until about 13,000 years ago, when the glaciers began to melt and opened a narrow ice-free corridor through western Canada into the present-day United States, and from there all the way down to South America. It was presumed that the Clovis people had been the first to travel through that corridor, and they could not have done so before 13,000 years ago.
But from the fossil mammoth bones found at the Monte Verde site, Dihellay knew that this camp had to be at least 11-12,000 years old, meaning that if humans had first entered North America 13,000 years ago, they had already reached the southern parts of South America within just 1-2,000 years. It was a very early and archaeologically significant site.
As a routine matter, Dihellay sent out some of the charcoal samples from the fire hearths he had uncovered to be radio-dated. But when he got the results, he was stunned. The charcoal was over 14,500 calendar years old (about 12,500 radio-carbon years).
Now, the significance of the Monte Verde site went off the scale. A human settlement in Chile at 14,500 years Before Present meant that their ancestors must have entered North America at minimum 15-16,000 years ago. But at that time, the whole northern Canada landmass was still covered by glacial ice over a mile thick, and a journey over that glacial ice would have been impossible. The whole timeline of the settlement of the western hemisphere would have to be re-thought.
Similar claims for “pre-Clovis” human settlements had been made before, and they were always met with a storm of controversy and generally rejected by the archaeological community. Dihellay knew that if his findings were to be taken seriously by science, he would have to be extraordinarily meticulous in his work, document every step of his excavation, and triple-check everything. For the next two decades, Dihellay brought in experts in a wide range of fields, over 85 all together, to carefully study everything that was uncovered–animal bones, wooden and stone tools, human footprints, human coprolites, hearth sites, post holes for wooden dwellings, sea shells from the coastline 30 miles away, and even scraps of animal hide and plant/seaweed fragments (including wild potato). At one point, a remnant of a chunk of meat was uncovered, still intact enough to be able to sequence its DNA (it turned out to be a piece of mastodon flesh). Dihellay invited open skeptics to come to the site and examine everything for themselves, often while an uncovered artifact was still embedded in the ground.
In 1997, after 20 years of excavations and study, Dihellay wrote up his findings, in a stunningly-detailed two-volume monograph totaling over 1400 pages. The Monte Verde site, he concluded, had been an open-air campsite located next to a stream at the edge of a forest. About 20-30 inhabitants had lived there for a period of one or two years before abandoning it. After the site was abandoned, a freshwater bog formed over the location, covering the entire site with peat and water, and the oxygen-free peat preserved the organic matter that it covered, allowing Dihellay to find perfectly-preserved organic artifacts that would normally have long ago rotted away. All of the radiocarbon dates from Monte Verde clustered around 12,500-12,800 calibrated-carbon years ago (about 14,600-14,800 calendar years ago). Although some archaeologists still remain skeptical, the scientific consensus today is that Monte Verde is indeed an authentic pre-Clovis site, which was inhabited at least 14,500 years ago, over 1,000 years before the earliest Clovis site.
So if the original migrants from Asia could not have crossed the glacial ice sheets in Canada, how did they get from Beringia all the way down to Chile, and when? The most widely-accepted hypothesis is that the original Siberian immigrants followed the ancient coastline, using boats. By travelling along the shoreline and feeding on fish and seafood, they could have moved relatively rapidly along the 8,000 miles of seacoast from Alaska to Chile. Because the sea level would have risen since that time as the Ice Age ended and the glaciers melted, any campsites they left behind would have been inundated and would now be unreachable under the Pacific Ocean. And because the Canadian glaciers would not have been an obstacle for them, they could have entered North America long before those glaciers melted, maybe before they had formed–perhaps even as early as 25-30,000 years ago. The “coastal migration” hypothesis could also explain why the sites in Chile are older than those in North America: it is possible that the immigrants from Asia moved along the coast as far as they could go, to the icy tip of South America, and then moved inland, therefore filling the western hemisphere from the bottom to the top, instead of from the top down as the Beringia land route proposed. (On the other hand, there are two potential pre-Clovis sites in North America, one in Pennsylvania and the other in Florida.)
But one thing is now certain: humans were in the western hemisphere at least 1,000 years earlier than had previously been believed.