Recent excavations have revealed sediment layers at White Sands National Park containing ancient grass seeds intermixed with soil. Researchers led by Bennett conducted radiocarbon dating on seeds found in the layers directly above and below the oldest and youngest footprints. Findings published in 2021 indicate that the oldest footprints date back to over 23,000 years ago, while the more recent ones were made before 21,000 years ago.
During this period, a significant portion of North America was covered by thick ice sheets, isolating the northern half of the continent. The discovery of footprints dating back 23,000 years suggests that human populations had already established themselves in present-day New Mexico prior to the ice sheets cutting off access from the southern parts of the continent for millennia.
Ancient human footprints found in situ at White Sands National Park in New Mexico.
Credit:
Jeffrey S. Pigati et al., 2023
However, the reliability of these results has faced scrutiny. Some experts have highlighted potential issues with the aquatic plant species (Ruppia cirrhosa) studied, which are known to absorb ancient carbon from groundwater. This contamination might have compromised the age estimations of the footprints. Additionally, pollen samples were extracted from different sediment layers than those containing the footprints.
In response to these concerns, the research team conducted further analyses, focusing on pollen from the same layers as the footprints, specifically from thicker samples. This pollen originated from terrestrial plants, including pine, spruce, and fir, effectively addressing earlier issues related to groundwater contamination. They also utilized a different dating method, optically stimulated luminescence, on quartz grains from sediments above the oldest footprint layer. Their findings, published in 2023, corroborate the earlier age estimates.
