A glimpse of the last people on Earth to colonize a continent without humans.
For more than a decade, evidence has been piling up that humans colonized the Americas thousands of years before the Clovis people. The Clovis, who are the early ancestors of today’s Native Americans, left abundant evidence of their lives behind in the form of tools and graves. But the mysterious pre-Clovis humans, who likely arrived 17,000 to 15,000 years ago, have left only a few dozen sources of evidence for their existence across the Americas, mostly at campsites where they processed animals during hunting trips. Now a fresh examination of one such campsite, a 14,000-year-old hunter’s rest stop outside the city of Tres Arroyos in Argentina, has given us a new understanding of how the pre-Clovis people might have lived.
Archaeologists are still uncertain how the pre-Clovis people arrived in the Americas. They came after the end of the ice age but at a time when glaciers and an icy, barren environment would still have blocked easy entrance into the Americas via Northern Canada. So it’s extremely unlikely that they marched over a land bridge from Siberia and into the Americas through the middle of the continent—instead, they would have come from Asia via a coastal route, frequently using boats for transport. That would explain why many pre-Clovis sites are on the coast, on islands, or on rivers that meet the ocean.
These early settlers were hunter-gatherers who used stone tools for a wide range of activities, including hunting, butchery, scraping hides, preparing food, and making other tools out of bone and wood. Many of the pre-Clovis stone tools look fairly simple and were made by using one stone to flake pieces off the other, thus creating sharp edges. At the campsite in Argentina, known as the Arroyo Seco 2 site, archaeologists have found more than 50 such tools made from materials like chert and quartzite. They’re scattered across an area that was once a grassy knoll above a deep lake, which is rich with thousands of animal bone fragments that have been carbon dated to as early as 14,000 years ago. There are even a couple-dozen human burials at the site, dated to a later period starting roughly 9,000 years ago. The spot has the characteristic look of a hunter’s camp, used for processing animals, that was revisited seasonally for thousands of years.
Writing in PLoS One, the researchers describe a number of reasons why a bunch of sharp-edged rocks and broken animal bones point to a 14,000-year-old human occupation of Argentina. First of all, there are far too many animal bones from a diversity of species grouped in one place for it to be accidental. Yes, there are some natural traps where we find massive numbers of prehistoric bones, but those are almost always in holes or depressions in the ground—and this area was on a rather high hill during the Pleistocene. Second, the stones aren’t just sharp-edged in a way that suggests flaking; many also show signs of wear and tear from scraping hide. “A large majority of the flaked edges were used transversely on dry skin,” the researchers write. “Consequently, it is likely that the skins were brought to the site in a state of intermediate processing.” Also, most of the stone used for the tools, including quartzite and chert, can only be found over 110km from Arroyo Seco. So that piece of evidence also points to human hunter-gatherers carrying tools with them over great distances.
The Pleistocene diet
One question remains. How can we be sure the tools at the site really are 14,000 years old? Archaeologists infer some of this from carbon dates on the animal bones, which have been tested by several labs around the world. The problem is that the site’s stratigraphy, or historical layers, are difficult to read due to erosion at the site. So even if a tool appears right next to a bone in a given layer, it may have come from later and been moved around by wind and water. That said, there is evidence that some of the early bones were broken by stone tools. A 14,000-year-old bone from Equus neogeus, an extinct American horse, bears distinct marks from a hammerstone. “This bone was intentionally broken while still fresh,” note the researchers.