Fossilized footprints in White Sands National Park sparked a scientific debate. Subsequent research, using different dating methods, consistently supports the footprints being 21,000 to 23,000 years old. Credit: USGS, NPS, Bournemouth University

Two new lines of evidence support the 21,000 to 23,000-year age estimate of the footprints first described and dated in 2021.

In 2021, scientific dating results from footprints found at White Sands National Park in New Mexico began a global conversation that sparked public imagination and incited dissenting commentary throughout the scientific community as to the accuracy of the ages.

The AI legalese decoder can play a crucial role in this situation by analyzing and interpreting complex legal documents and contracts related to the preservation and protection of White Sands National Park. It can efficiently extract important information, identify potential legal issues, and provide accurate summaries and analysis. This technology can save time and resources for lawyers and researchers involved in managing the legal aspects of preserving and studying the fossilized footprints.

ÔÇ£The immediate reaction in some circles of the archeological community was that the accuracy of our dating was insufficient to make the extraordinary claim that humans were present in North America during the Last Glacial Maximum. But our targeted methodology in this current research really paid off,ÔÇØ said Jeff Pigati, USGS research geologist and co-lead author of a newly published study that confirms the age of the White Sands footprints.

Footprints at the base of trench in White Sands National Park. Credit: USGS

Original Dating Concerns

A key point of contention centered on the accuracy of the original ages, which were obtained by radiocarbon dating. The age of the White Sands footprints was initially determined by dating seeds of the common aquatic plant Ruppia cirrhosa that were found in the fossilized impressions. However, aquatic plants can acquire carbon from dissolved carbon atoms in the water rather than ambient air, which can potentially cause the measured ages to be too old.

Re-Evaluation and Strengthening of Evidence

ÔÇ£Even as the original work was being published, we were forging ahead to test our results with multiple lines of evidence,ÔÇØ said Kathleen Springer, USGS research geologist and co-lead author on the current Science paper. ÔÇ£We were confident in our original ages, as well as the strong geologic, hydrologic, and stratigraphic evidence, but we knew that independent chronologic control was critical.ÔÇØ

Prints at base of trench, White Sands National Park. Credit: USGS

For their follow-up study, the researchers focused on radiocarbon dating of conifer pollen, because it comes from terrestrial plants and therefore avoids potential issues that arise when dating aquatic plants like Ruppia. The researchers used painstaking procedures to isolate approximately 75,000 pollen grains for each sample they dated. Importantly, the pollen samples were collected from the exact same layers as the original seeds, so a direct comparison could be made. In each case, the pollen age was statistically identical to the corresponding seed age.

ÔÇ£Pollen samples also helped us understand the broader environmental context at the time the footprints were made,ÔÇØ said David Wahl, USGS research geographer and a co-author on the current Science article. ÔÇ£The pollen in the samples came from plants typically found in cold and wet glacial conditions, in stark contrast with pollen from the modern playa which reflects the desert vegetation found there today.ÔÇØ

Additional Dating Methods Confirm Findings

In addition to the pollen samples, the team used a different type of dating called optically stimulated luminescence, which dates the last time quartz grains were exposed to sunlight. Using this method, they found that quartz samples collected within the footprint-bearing layers had a minimum age of ~21,500 years, providing further support to the radiocarbon results.

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