Discovery of human footprints at White Sands, New Mexico, dated to between 21,000 and 23,000 years ago, was a notable step in understanding the initial peopling of the Americas, but that work was met with criticism focused on the reliability of the materials used in the radiocarbon dating: seeds of the common aquatic plant Ruppia cirrhosa and conifer pollen grains. A new study led by University of Arizona researcher Vance Holliday marks the third type of material — ancient mud in paleolake Otero — used to date the footprints, and shows that the mud is between 20,700 and 22,400 years old.
The ancient human footprints found at White Sands National Park in New Mexico, the United States. Image credit: Bennett et al., doi: 10.1126/science.abg7586.
Traditionally, scientists believed that humans arrived in North America around 16,000 to 13,000 years ago.
However, the footprints at White Sands showed human activity in the area occurred between 23,000 and 21,000 years ago — a timeline that would upend our understanding of when cultures developed in North America.
It would make the prints about 10,000 years older than remains found 90 years ago at a site near Clovis, New Mexico, which gave its name to an artifact assemblage long understood by archaeologists to represent the earliest known culture in North America.
Critics have spent the last four years questioning the two previous studies, largely arguing that the ancient seeds and pollen in the soil used to date the footprints were unreliable markers.
“It’s a remarkably consistent record. You get to the point where it’s really hard to explain all this away,” Dr. Holliday said.
“As I say in the paper, it would be serendipity in the extreme to have all these dates giving you a consistent picture that’s in error.”
Millennia ago, White Sands was a series of lakes that eventually dried up.
Wind erosion piled the gypsum into the dunes that define the area today.
The footprints were excavated in the beds of a stream that flowed into one such ancient lake.
“The wind erosion destroyed part of the story, so that part is just gone. The rest is buried under the world’s biggest pile of gypsum sand,” Dr. Holliday said.
For the latest study, Dr. Holliday and colleagues returned to White Sands in 2022 and 2023 and dug a new series of trenches for a closer look at the geology of the lake beds.
“It’s a strange feeling when you go out there and look at the footprints and see them in person,” said Jason Windingstad, a doctoral candidate at the University of Arizona.
“You realize that it basically contradicts everything that you’ve been taught about the peopling of North America.”
The authors acknowledge that their study doesn’t address a question they heard from critics since 2021: Why are there no signs of artifacts or settlements left behind by those who made the footprints?
“It’s a fair question. Some of the footprints uncovered for the 2021 study were part of trackways that would have taken just a few seconds to walk,” they said.
“It’s perfectly reasonable to assume that hunter-gatherers would be careful not to leave behind any resources in such a short time frame.”
“These people live by their artifacts, and they were far away from where they can get replacement material.”
“They’re not just randomly dropping artifacts. It’s not logical to me that you’re going to see a debris field.”
The team’s new results appear in the journal Science Advances.
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Vance T. Holliday et al. 2025. Paleolake geochronology supports Last Glacial Maximum (LGM) age for human tracks at White Sands, New Mexico. Science Advances 11 (25); doi: 10.1126/sciadv.adv4951
