Human footprints found in an ancient lakebed in White Sands National Park, New Mexico date to between 21,000 years and 23,000 years ago, according to new findings that bolster a much-debated study from 2021.
The lightning-rod paper ran counter to the generally held scientific position that humans didn’t arrive in the Americas until between 13,000 years and 16,000 years ago. Prior to that – during the Last Glacial Maximum – massive glaciers would have impeded human migration from modern-day Siberia.
Scientists questioned the radiocarbon dating used in the 2021 study, which relied on seeds from an underwater grass plant called Ruppia cirrhosa. Spread throughout layers of sand and clay, the seeds served as markers from different time periods, the paper argued. But critics warned that the parent plants could have absorbed different carbon-14 from the water and produced results that skewed far too old.
Researchers have dated these ancient footprints three different ways. (Credit: USGS/NPS/Bournemouth University)
Now, researchers from the first team have returned with two new lines of evidence about the White Sands footprints, and both have confirmed the initial, jaw-dropping date range.
The team performed new radiocarbon dating using conifer pollen taken from the same layers as the grass seeds. Coming from above-ground plants, the conifer material avoids the original hang-up associated with the Ruppia seeds.
Despite the different plant sources, the two dating methods produced results that were “statistically identical,” according to a statement.
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USGS scientists examine fossilized footprints in White Sands National Park. (Credit: USGS)
The team also performed a dating method on the fossilized footprints called Optically Stimulated Luminescence (OSL) that detects how much time has passed since quartz grains in sediment received sunlight. According to those findings, the footprints were at least 21,500 years old.
“With three separate lines of evidence pointing to the same approximate age,” the statement said, “it is highly unlikely that they are all incorrect or biased and, taken together, provide strong support for the 21,000 to 23,000-year age range for the footprints.”
These American ancestors would have lived alongside such megafauna as wooly mammoths and giant sloths, which didn’t disappear from North America until about 11,000 years ago.
Scientists excavated a trench to reach the oldest footprints. (Credit: USGS)
Such early human settlement also presents an obvious mystery – how did people travel from Asia to the Americas during the Last Glacial Maximum?
“At that time, there was a huge, mile-high mountain range of ice covering Canada to the north, and the pathway down the Pacific Coast wasn’t very accommodating either,” said David Rhode, a paleoecologist at the Desert Research Institute, in a 2022 statement. “It may have been that people had to come here much earlier than that.”
Once they made it to modern-day New Mexico, these ancestors seemed to possess some division of labor, as exhibited by the ice age footprints, most of which fit the feet of children. This suggests that the younger people performed the “fetch” work of the settlements, the 2021 paper says, by grabbing wood or stones for adults who performed more skilled tasks.
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