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

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Fossilized footprints in White Sands National Park have sparked scientific controversy. Subsequent research, using various dating methods, consistently supports that the footprints are between 21,000 and 23,000 years old. Credit: USGS, NPS, Bournemouth University

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

In 2021, the results of scientific dating of footprints found in White Sands National Park in New Mexico began a global conversation that has sparked the public’s imagination and generated dissenting commentary throughout the scientific community regarding the topic. Accuracy From the ages.

“The immediate reaction in some circles of the archaeological community was that the accuracy of our dating was insufficient to make an extraordinary claim that humans were present in North America during the last glacial maximum,” said Jeff Bigatti, a research geologist at the USGS and co-lead author. A newly published study confirms the age of the white sand footprints, “but our targeted methodology in this current research has really paid off.”

Footprint of the base of the trench in White Sands National Park

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

Original dating concerns

The main point of contention centered on the accuracy of the original ages, which were obtained by radiocarbon dating. The age of the white sand footprints was initially determined by dating seeds of common aquatic plants Rubia cirrhosis Which are found in fossilized impressions. However, aquatic plants can gain carbon from carbon atoms dissolved in the water rather than the surrounding air, which can cause the measured ages to be too old.

Re-evaluation and strengthening of evidence

“Even while publishing the original work, we were moving forward to test our findings using multiple lines of evidence,” said Kathleen Springer, a research geologist at the USGS and co-lead author on the current research. Sciences paper. “We were confident in our original ages, as well as the strong geological, hydrological and stratigraphic evidence, but we knew that independent temporal control was critical.”

Base of the footprints of Trench White Sands National Park

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

In their follow-up study, the researchers focused on radiocarbon dating of conifer pollen, because it comes from terrestrial plants, thus avoiding potential problems that arise when dating aquatic plants like Rubia. 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 layers as the original seeds, so a direct comparison can be made. In each case, the pollen age was statistically identical to the corresponding seed age.

“The pollen samples also helped us understand the broader environmental context at the time the footprints were made,” said David Wahl, a research geographer at the USGS and co-author of the current study. Sciences condition. “The pollen in the samples came from plants typically found in cold, wet, glacial conditions, in stark contrast to pollen from modern playa that reflects the desert plants found there today.”

Additional dating methods confirm the results

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

With three separate lines of evidence indicating the same approximate age, they are all unlikely to be incorrect or biased, and together provide strong support for the 21,000 to 23,000 year age range for the footprints.

Reference: “Independent Age Estimates Resolve Controversy Over Ancient Human Footprints at White Sands” by Jeffrey S. Bigatti, Kathleen B. Springer, Jeffrey S. Honke, David Wahl, Mary R. Vincent L. Santucci, Daniel Udis, David Bustos, and Matthew R. Bennett, October 5, 2023, Sciences.
doi: 10.1126/science.adh5007

The research team included scientists from the US Geological Survey, Lawrence Livermore National Laboratory, the National Park Service, and academic institutions. Their ongoing studies at White Sands focus on the 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.

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