New Evidence Suggests Humans Arrived in the Americas Before Ice Age

Tens of thousands of years ago, a giant lake rested inside the Tularosa basin which sits in what is now southern New Mexico and West Texas. At that time, the area was a lush grassland and much less arid, but over time it dried into a desert with the park's trademark sand dunes.

Human footprint fossils found at White Sands National Park in New Mexico have been dated to between 21,000 and 23,000 years ago, lending more evidence to the theory humans arrived in the Americas long before previously thought.

Published on Thursday in the journal Science, the findings back up a previous study that was doubted by some researchers. In 2021, the footprints were estimated using radiocarbon dating methods on seeds from aquatic plants. But there were concerns that those seeds may have absorbed ancient carbon which could have thrown off the results.

The new study used ancient conifer pollen from the same sedimentary layer where the footprints were found and examined grains of quartz using a method that reveals when they were last exposed to light. Both methods backed up the original study, with the pollen dating between 21,000 and 23,000 years ago and the quartz being buried between 21,400 and 18,000 years ago.

These dates would suggest humans lived in the Americas during the last Ice Age.

For years, researchers believed humans did not arrive in the Americas until around 16,000 years ago at the earliest, after the Ice Age and right before the Bering land bridge, which connected Russia and Alaska, was covered by rising sea levels.

Study co-author Jeffrey Pigati, a geologist at the US Geological Survey, says the ages “are statistically indistinguishable from our original seed ages.”

Archeologists looking for evidence of early human settlers in the Americas have tended to focus on the Pacific coast because ice glaciers from the last Ice Age would have prevented travel from the Bering land bridge, but if humans were in New Mexico 21,000 years ago, they may have arrived just before the glaciers formed.

Some researchers remain skeptical. Loren Davis, an archaeologist at Oregon State University, says it is possible the clay containing the quartz grains may have come from the lake floor and then got redeposited on top of the younger lakeshore mud that covered the footprints. He also adds the sediment covering the footprints may have been blown there after being eroded from older rocks.

However, the study co-authors insist there is no evidence that either of those scenarios took place. And even Davis agrees archeologists should start looking for evidence of human habitation from before the Ice Age.

If they are right, "it resets the playing field of what’s possible," Davis admitted.

There have been a few other discoveries in recent years that point to pre-Ice Age colonization of the Americas by humans. In July, a study was published covering pendants made from ancient and now-extinct giant sloths that were found in Brazil. It was previously assumed ancient humans simply found the bones of the extinct animals, but the study suggested they were made between 25,000 and 27,000 years ago. Researchers believe the sloths went extinct roughly 10,000 years ago.

Another study of a giant sloth boneyard found in Uruguay suggested early humans may have hunted and eaten the massive animals as early as 30,000 years ago. Megatherium, the giant ground sloth of South America, grew up to 20 feet (6 meters) in length and weighed up to 8,800 pounds (nearly 4,000 kilograms). Footprints of the giant sloths were also found at the White Sands National Park, along with many other animals including dogs and camels.