“Mud never lies,” added University of Arizona archaeologist Vance Holliday, whose new work has turned a century of hypothesis on its head as to when and how humans first settled the Americas. For generations, the conventional Clovis-first hypothesis assumed the continent’s first inhabitants arrived around 13,000 years ago and left common stone tools in North America. But a fossil record of ancient footsteps, embedded in the mud of an ancient lake at White Sands National Park, New Mexico, has now changed that story by almost 10,000 years.
The story started in 2019, when archaeologists from the U.S. National Park Service and Bournemouth University discovered human trackways under deposits of gypsum sand layers. Early radiocarbon dating of pollen and seeds put the footprints at between 21,000 and 23,000 years, a time during the Last Glacial Maximum when ice caps covered most of the northern hemisphere. The implications were dramatic: if true, the tracks would be the oldest direct human mark in the Americas by thousands of years, older even than the Clovis culture. “You realize that it basically contradicts everything that you’ve been taught about the peopling of North America,” said Jason Windingstad, a doctoral candidate who participated in the fieldwork.
Skepticism, however, was swift and pointed. Critics questioned the reliability of dating aquatic plants such as Ruppia cirrhosa, which can absorb ancient carbon from lake water and yield artificially old dates. As a result, Holliday’s group went back to White Sands in 2022 and 2023 and this time sampled and dated directly the mud from the ancient lakebed itself. The samples were run through two different laboratories, both of which produced the same date range: 20,700 to 22,400 years ago. This new information is the third kind of material mud, as well as seeds and pollen employed to date the site, and the third lab to validate the results.
With 55 radiocarbon dates now all falling within one period of time, consistency is impressive. “It’s a remarkably consistent record,” Holliday said to Science Advances. “You get to the point where it’s really hard to explain all this away. 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”. The prints, incredibly well preserved in what was at the time a lush wetland, provide a glimpse of intimate and unexampled quality into the lives of Ice Age hunter-gatherers. The absence of artefacts, no tools, no camp has puzzled some archaeologists, but Holliday has a common-sense solution: “These people live by their artefacts, 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 technological advance that enabled the breakthrough is as fascinating as the footprints themselves. Radiocarbon dating, since its discovery in the middle of the 20th century, has undergone a succession of improvements from accelerator mass spectrometry, which made it possible to analyze infinitesimal samples, to compound-specific dating of individual molecules. The White Sands research is rare in its meticulous cross-dating: of seeds, pollen, and now mud, each with potentially distinct biases, and cross-checking results between laboratories. That level of gravity represents a broader trend within archaeological science, with improvements in analytical potential balanced by rigorous quality control requirements and data sharing.
But even as the dating techniques become increasingly stringent, controversy over peopling of the Americas is by no means resolved. Clovis-first orthodoxy, based on 1930s New Mexico discovery of diagnostic fluted spear points, long dominated textbooks and museum displays. Genetic research, though, indicates a complicated brocade of northeast Asian migrations, with population differentiation and expansion occurring from 24,900 to 13,000 years ago. There are a few theories that suggest inland migration along an ice-free corridor and others support Pacific coastal migration, taking advantage of sea resources on the “kelp highway.” The White Sands footprints, firmly dated at the Last Glacial Maximum, are proof that humans were present on the continent when most of it was still in ice.
The prints themselves are a silent witness. Imprinted in the bottoms of fossilized stream channels that once supplied water to Lake Otero, they chronicle the journeys of small groups possibly family groups over a wetland teeming with Ice Age animals. Some of the tracks, scientists clarify, would have been walked in seconds. The lack of supporting artifacts is not surprising for highly nomadic hunter-gatherers, particularly in a place where all tools were valuable and resources were limited.
The implications cascade. If humans did exist in North America over 20,000 years ago, it attests to an earlier and possibly more evolved migration and adaptation process than has been previously depicted. It also presents new questions regarding the paths taken along the Pacific rim, via interior passageways, or via multiple routes and regarding the dynamics of interactions between these first Americans and the worlds they encountered.
As radiocarbon analysis and laboratory techniques improve, scientists will be able to more accurately date human dispersal chronology. New technology in compound-specific radiocarbon analysis, for instance, now makes it possible to date single amino acids from bones that were not unusually well preserved, settling disputed archaeological timelines. And as increasingly genetic, geologic, and archaeological information is synthesized, increasingly detailed light will be cast on the remote history of human movement in the Americas.
So there on the gypsum dunes of White Sands, researchers are reminded that each footprint is at once a data point and a tale one that continues to challenge, refine, and add to our knowledge of the human condition.
