The 2021 outcomes started a worldwide dialog that sparked public creativeness and incited dissenting commentary all through the scientific neighborhood as to the accuracy of the ages.
“The rapid response in some circles of the archeological neighborhood was that the accuracy of our relationship was inadequate to make the extraordinary declare that people had been current in North America in the course of the Final Glacial Most. However our focused methodology on this present analysis actually paid off,” mentioned Jeff Pigati, USGS analysis geologist and co-lead writer of a newly revealed examine that confirms the age of the White Sands footprints.
The controversy centered on the accuracy of the unique ages, which had been obtained by radiocarbon relationship. The age of the White Sands footprints was initially decided by relationship seeds of the widespread aquatic plant Ruppia cirrhosa that had been discovered within the fossilized impressions. However aquatic crops can purchase carbon from dissolved carbon atoms within the water reasonably than ambient air, which may doubtlessly trigger the measured ages to be too outdated.
“Whilst the unique work was being revealed, we had been forging forward to check our outcomes with a number of traces of proof,” mentioned Kathleen Springer, USGS analysis geologist and co-lead writer on the present Science paper. “We had been assured in our authentic ages, in addition to the robust geologic, hydrologic, and stratigraphic proof, however we knew that unbiased chronologic management was important.”
For his or her follow-up examine, the researchers centered on radiocarbon relationship of conifer pollen, as a result of it comes from terrestrial crops and due to this fact avoids potential points that come up when relationship aquatic crops like Ruppia. The researchers used painstaking procedures to isolate roughly 75,000 pollen grains for every pattern they dated. Importantly, the pollen samples had been collected from the very same layers as the unique seeds, so a direct comparability might be made. In every case, the pollen age was statistically an identical to the corresponding seed age.
“Pollen samples additionally helped us perceive the broader environmental context on the time the footprints had been made,” mentioned David Wahl, USGS analysis geographer and a co-author on the present Science article. “The pollen within the samples got here from crops sometimes present in chilly and moist glacial situations, in stark distinction with pollen from the trendy playa which displays the desert vegetation discovered there immediately.”
Along with the pollen samples, the staff used a special kind of relationship referred to as optically stimulated luminescence, which dates the final time quartz grains had been uncovered to daylight. Utilizing this technique, they discovered that quartz samples collected throughout the footprint-bearing layers had a minimal age of ~21,500 years, offering additional assist to the radiocarbon outcomes.
With three separate traces of proof pointing to the identical approximate age, it’s extremely unlikely that they’re all incorrect or biased and, taken collectively, present robust assist for the 21,000 to 23,000-year age vary for the footprints.