What's the earliest evidence of humans in the Americas?

The arrival and establishment of humans in the Americas was a key step in humanity's trek across the planet, but exactly when this milestone was achieved remains hotly contested. According to the evidence we have now, when did the first humans arrive in North America? 

Based on stone artifacts dating to about 13,000 years ago, archaeologists for most of the 20th century suggested that the prehistoric Clovis culture was the first to migrate to the Americas. However, the site of Monte Verde in southern Chile, first discovered in 1975, was found to be about 14,200 years old. If people made it that far down in South America by that point — either after their ancestors crossed over the Bering Land Bridge that once connected Asia and North America, or traveling in watercraft along Pacific coasts  — then earlier sites must exist in North America, Michael Waters, a geoarchaeologist at Texas A&M University, told Live Science.

Starting in 2009, archaeologists began excavating deposits at the Cooper's Ferry site in Idaho. Radiocarbon dating of human projectile points in these deposits revealed that people found their way inland into North America by about 16,000 years ago, Waters noted. Cooper's Ferry may be the oldest strong evidence of human settlement of the continent yet, and unpublished research from 2023 describes slightly older evidence; stone tools next to animal teeth dated to 18,000 years ago in Oregon. However, scientists recently found controversial signs of even older sites in North America. 

In 2020, archaeologists digging in Chiquihuite Cave in the Astillero Mountains of central Mexico unearthed about 1,900 stone artifacts. Radiocarbon and optically stimulated luminescence dating of the objects suggested that humans might have occupied the area 31,000 to 33,000 years ago. 

Later, in 2021, scientists tested 60 human footprints embedded in an ancient lake bed in what is now White Sands National Park in south central New Mexico. By using carbon-dating methods on seeds found in sediments within the prints, they suggested that people occupied the New World between about 21,000 and 23,000 years ago. 

However, there are problems with the claims made at both the Chiquihuite and White Sands sites, Matthew Des Lauriers, an archaeologist at California State University, San Bernardino, told Live Science.

When it comes to Chiquihuite, even the scientists who excavated the site noted that others might argue that the oldest stone objects discovered there are not of human origin but are merely "geofacts," or normal rocks that look artificial. A 2021 study from an independent group indeed made that argument.

As for White Sands, the footprints are clearly human, Waters noted. But he noted that ancient plant samples used to date the footprints may seem older than their true age.

"The footprints have real problems with the dating," Des Lauriers said. Waters estimated the prints may actually be only about 15,000 years old.

A number of claims based on stone artifacts discovered in Brazil suggested that humans may have reached sites there, such as Pedra Furada, about 35,000 years ago, Waters noted. However, a 2022 study revealed that these artifacts may actually have been created by capuchin monkeys as they used rocks to break open nuts, he added. 

But other evidence is emerging of early human occupation in South America. A 2023 study found 27,000-year-old sloth bones crafted by humans into pendants from Brazil.

New ideas often come and go about the people of the Americas. For instance, "a few years back, it was suggested that people came from western Europe to the Americas, the 'Solutrean hypothesis,'" Waters said. However, "recent genetic work on Solutrean human remains shows that they are not at all related in any way to the Indigenous peoples of the Americas. Thus, this hypothesis can be discarded."

All in all, "the public needs to know that archaeology is a process," Waters said. "Science follows a course — publication of new data, vetting of that data, more testing, and acceptance or rejection of ideas. This is a slow and careful process."