For most 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 by around 13,000 years ago had given rise to the Clovis culture, the earliest widely accepted evidence of human presence on the continent. It was a tidy, well-defended consensus. Then, in 2019, archaeologists digging in the gypsum dunes of White Sands National Park in New Mexico pulled something out of the ground that the consensus could not absorb: a set of fossilised human footprints so old they had been pressed into mud during the peak of the last Ice Age, when the land bridge those same humans were supposedly still waiting to cross had not yet opened.

How scientists dated the footprints and why it caused a controversy

The original 2021 study, published in the journal Science, dated the footprints using radiocarbon analysis of seeds from an aquatic plant called Ruppia cirrhosa found in the sediment layers immediately above and below the tracks. The results placed the footprints between 21,000 and 23,000 years ago squarely within the Last Glacial Maximum, the coldest and most extreme phase of the last Ice Age, when massive ice sheets covered much of the northern hemisphere.The dates were immediately contested. Critics argued that aquatic plant seeds 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 substantive enough to cast genuine doubt over what was otherwise a landmark finding.

How the White Sands footprints survived for 23,000 years

White Sands National Park sits in the Tularosa Basin of southern New Mexico, a landscape defined today by rolling dunes of fine white gypsum, one of the most visually striking geological features in North America. Beneath those dunes lies a different world entirely: the dried bed of an ancient lake called Lake Otero, which existed during the last Ice Age when the region’s climate was wetter and cooler than it is today. It was along the muddy shoreline of that vanished lake that the footprints were made and preserved.The tracks were excavated by a team from Bournemouth University in collaboration with the US National Park Service. They were found buried in multiple layers of sediment, pressed into the ancient lakebed mud and left there by people who walked, stood, and moved along the shoreline tens of thousands of years ago. Many of the tracks were made by children and teenagers, a detail that has struck researchers as quietly extraordinary, the preserved evidence of young people going about their lives in a landscape that no longer exists.

How the independent studies finally settled the debate

The controversy prompted researchers to return to the site with different dating methods entirely. 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 separate techniques: optically stimulated luminescence and radiocarbon dating of the pollen itself. Both methods returned dates of 20,000 to 23,000 years ago, statistically indistinguishable from the original seed-based results.

What the footprints mean for the Clovis First theory

The implications for the long-held 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 understood to represent the earliest known human presence in North America, dating to around 13,000 years ago. The White Sands footprints are at least 8,000 years older than we thought.More striking still is what the timing means geographically. During the Last Glacial Maximum, the two primary corridors through which humans are thought to have migrated into 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 not yet accessible. If humans were already in New Mexico 23,000 years ago, they must have arrived before those routes closed, suggesting either a much earlier migration than any existing model accounts for, or an alternative route into the continent that has not yet been identified.

What was walking around White Sands 23,000 years ago

The footprints do not exist alone. The sediments at White Sands have also yielded tracks from the 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 wetland, populated by megafauna that the humans living alongside them likely hunted.“It’s just screamingly obvious” that humans made these tracks, said Vance Holliday, who has worked at White Sands since 2012. The question was never really whether the footprints were human. It was when. After four years of scientific debate, three independent dating methods, and three separate studies all arriving at the same answer, that question appears, at last, to be settled.