White Sands fossil footprints

The White Sands fossil footprints are a set of fossilized human footprints discovered in 2009 in the White Sands National Park in New Mexico. In 2021 they were radiocarbon dated, based on seeds found in the sediment layers, to between 21,000 and 23,000 years ago. That date range is currently the subject of scientific debate, but if it is correct, the footprints would be one of, if not the oldest record of humans in the Americas. The earlier theory held that human settlement of the Americas began at the end of the last Ice Age, about 13,000-16,000 years ago.

Fossil footprints from White Sands National Park

Description

More fossil footprints from White Sands National Park

The 61 footprints are located at the shore of a dried up ice age era lake, Lake Otero in the Tularosa Basin. The prints were laid on the shores of the now-dry lake at a time when the climate in the region was less arid. Instead of being an arid desert of gypsum dunes, the region had extensive grasslands and abundant vegetation.

The prints were found in seven soil layers and provide evidence of human occupation spanning approximately 2000 years. The prints have "good anatomical definition (i.e. visible heel impressions, medial longitudinal arches and toe pads)". They are flatter-footed than those that are left by people who habitually wear shoes and, in this respect, are similar to fossil footprints found in Namibia. The tracks are those of extinct megafauna, such as Columbian mammoths and ground sloths, as well as those of predators such as the American lion and dire wolves.

Interpreting the prints

Fossil footprint of a giant ground sloth found in White Sands National Park

The prints provide several insights into the lives of the peoples who made them. First, one set of prints appears to show human hunters tracking a giant sloth. Variations in the tracks left by the sloth show that it stood on its hind legs and spun around, possibly showing fear, but there is no evidence that the hunt was successful.

Second, another set of prints seems to have been laid by a woman or adolescent male, walking with a very young child for over a mile. It appears that the person sometimes carried the child and then set it down, slipping as he or she carried the additional weight. The pair made a round trip journey and, between the outbound and return legs of the trip, a mammoth crossed their track without changing course or showing signs of concern about their presence.

Third, the vast majority of the prints were made by teenagers and children, with few large adult footprints being found in any of the excavated surfaces. One explanation of this finding is that the teenagers and children were assigned tasks such as 'fetching and carrying' near the lake bed, whereas the adults engaged in more skilled activities.

It is thought that, counting both human and animal tracks, there are hundreds of thousands of fossilised footprints in the White Sands area. A report by the United States National Park Service states that the "fossilized footprints of White Sands are probably the most important resources in the Americas to understand the interaction of humans and extinct animals from the ice age."

Controversy about dating

In 2022, skeptics noted that age estimates relied on carbon dating Ruppia cirrhosa seeds, whose parent plants can intake older carbon from groundwater, thereby potentially resulting in dates thousands of years too old. A study accounting for this effect suggesting that the maximum age of the footprints is likely only 15,500–13,500 is calibrated years Before Present, which is similar to the dates found for many other archaeological sites across the Americas.

A 2023 study that included radiocarbon dating of pollen and optically stimulated luminescence dating (OSL dating) of quartz grains within the footprint layers corroborated the original dates obtained from the seeds. However, these dates have also been considered uncertain by other authors, who suggest that they represent maximum ages, rather than true age estimates, due to the OSL dating being only taken from a layer below the footprints, and the potential for old pollen to be eroded and redeposited into younger layers.