For much of the twentieth century, the story of how humans arrived in North America felt settled. They came from Siberia, crossed a land bridge called Beringia, moved south as the ice sheets retreated, and gave rise to the Clovis culture about 13,000 years ago, the earliest widely accepted evidence of human presence on the continent. It was a well-organized, well-secured consensus. Then, in 2019, archaeologists digging in the gypsum dunes of White Sands National Park in New Mexico uncovered something from the ground that couldn’t be unanimously absorbed: a set of fossilized human footprints so old that they were buried in the soil during the peak of the last ice age, when the land bridge that those same humans were still waiting to cross had not yet opened.

How scientists determined the date of the footprints and why there was controversy over it

The original 2021 study, published in the journal Science, dates the footprints using radiocarbon analysis of seeds of an aquatic plant called Rupiah cirrhosa, found in sediment layers just above and below the tracks. The results placed the footprints, dated to 21,000 to 23,000 years ago, within the Coldest and most extreme phase of the last ice age, the Last Glacial Maximum, when vast ice sheets covered much of the Northern Hemisphere.The dates were immediately disputed. Critics argued that seeds of aquatic plants are unreliable radiocarbon markers because they can absorb ancient dissolved carbon from groundwater, a phenomenon known as the reservoir effect, which can make materials appear older than they actually are. The debate was so abstract as to cast real doubt on what was otherwise an historical discovery.

How did the White Sands footprints survive for 23,000 years?

White Sands National Park is located in the Tularosa Basin of southern New Mexico, a landscape today defined by fine white gypsum dunes, one of the most striking geological features in North America. Beneath those dunes lies a different world altogether: the dry bed of an ancient lake called Otero Lake, which existed during the last ice age when the area’s climate was wetter and cooler than today. It was along the muddy shoreline of that lost lake where the footprints were made and preserved.The track was excavated by a team from Bournemouth University in collaboration with the US National Park Service. They were found buried in several layers of sediment, pressed into ancient lakeshore soil and left there by people who walked, stood and moved along the shoreline thousands of years ago. Many of the tracks were made by children and teenagers, a detail that has left researchers quietly extraordinary, with young people preserving evidence about their lives in a landscape that no longer exists.

How independent studies finally settled the debate

The controversy prompted researchers to return to the site with completely different dating methods. A study published in Science in 2023, led by Jeff Pigati of the US Geological Survey, dated pollen grains and quartz crystals from the same sediment layers using two different techniques: optically stimulated luminescence and radiocarbon dating of the pollen. Both methods returned dates of 20,000 to 23,000 years ago, which were statistically indistinguishable from the original seed-based results.

What do the footprints mean for the Clovis I theory

The implications of the long-standing Clovis First model are significant and irreversible. The Clovis culture, named after a site near Clovis, New Mexico, where distinctive stone tools were found in the 1930s, was long thought to represent the earliest known human presence in North America, about 13,000 years ago. The footprints at White Sands are at least 8,000 years older than we thought.What is even more surprising is what time means in geographical terms. During the Last Glacial Maximum, the two primary corridors through which humans migrated to the Americas, the ice-free corridor east of the Rocky Mountains and the coastal route along the Pacific, were either blocked by ice sheets or were not yet accessible. If humans were already in New Mexico 23,000 years ago, they would have arrived before those routes closed, which suggests either a much earlier migration than any current models, or an alternative route across the continent that has not yet been identified.

What was roaming around White Sands 23,000 years ago

Footprints do not exist alone. The sediments at White Sands also contain traces of animals that shared the lakeshore with these early humans: mammoths, giant ground sloths, and ancient camels, all of which are now extinct. The picture that emerges is of a functioning Ice Age ecosystem: a lake surrounded by grass and wetlands, populated by megafauna, presumably hunted by the humans who lived with them.Vance Holliday, who has been working at White Sands since 2012, said it is “absolutely clear” that humans made these tracks. The question was never really whether the footprints were human. This was when. After four years of scientific debate, three independent dating methods, and three separate studies arriving at a single answer, at last, the question appears to be settled.