Ancient footprints in New Mexico change the timeline for early human presence in North America

Two new sources support the first described and dated 2021 age estimate of 21,000 to 23,000 years.

In 2021, the results of scientific dating of footprints discovered in White Sands National Park in New Mexico sparked a global conversation, sparking public imagination and controversy throughout the scientific community. Accuracy of ages.

“The immediate reaction in some circles of the archaeological community was that our dating precision was insufficient to make the extraordinary claim that humans were present in North America during the Last Glacial Maximum. But in this current research our targeted method really paid off,” said a USGS research geologist who confirmed the age of the White Sand footprints in the newly published paper. said Jeff Picati, co-lead author of the study.

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

Original dating concerns

A major debate centers on the accuracy of the original ages obtained by radiocarbon dating. The age of the white sand footprints was initially determined by dating the seeds of a common aquatic plant Ruppia cirrhosa They are found in the fossil record. However, aquatic plants can obtain carbon from carbon atoms dissolved in water rather than from ambient air, making the measured age much older.

Re-evaluation and strengthening of evidence

“Although the original work has been published, we are moving forward to test our conclusions with multiple sources,” said USGS research geologist and current co-lead author Kathleen Springer. Science Paper. “We were confident in our original age and strong geological, hydrological and stratigraphic evidence, but we knew that independent chronological control was important.”

Printed at the bottom of the trench, White Sands National Park. Credit: USG

For their follow-up study, the researchers focused on radiocarbon dating of cone pollen because it comes from terrestrial plants and therefore avoids potential problems when dating aquatic plants such as 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 same plots as the original seeds, so direct comparisons were possible. In each case, pollen age was statistically similar to the corresponding seed age.

“The pollen samples helped us understand the broader ecological context at the time the footprints were made,” said David Wall, a USGS research geologist and current co-author. Science Article. “The pollen in the samples came from plants typically found in cold and wet glaciated conditions, in stark contrast to the pollen from modern playa that reflects the desert plants found there today.”

Additional dating methods confirm the findings

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

With three separate sources pointing to the same approximate age, it is highly unlikely that they are all wrong or biased, and taken together provide strong support for a 21,000 to 23,000 age range for the footprints.

Note: Jeffrey S. Picati, Kathleen B. Springer, Jeffrey S. Hohnke, David Wall, Mary R. Champagne, Susan RH. Zimmerman, Harrison J. Gray, “Independent Age Estimates Resolve Controversy of Ancient Human Footprints in White Sand,” Vincent L. Sanducci, Daniel Odes, David Bustos, and Matthew R. Bennett, 5 October 2023, Science.
DOI: 10.1126/science.adh5007

The research team included scientists from the USGS, Lawrence Livermore National Laboratory, the National Park Service, and academic institutions. Their ongoing studies at White Sands focus on environmental conditions that allowed people to thrive in southern New Mexico during the Last Glacial Maximum and are supported by the Climate Research and Development Program. US Geological Survey and USGS-NPS Natural Resources Conservation Program.