ARI SHAPIRO, HOST:
How long have humans lived on this continent? Well, one prevailing answer for decades was about 14,000 years, based on the age of early human stone tools. Now new findings add weight to the case for a longer human history in the Americas. Alice Fordham of member station KUNM in New Mexico reports.
ALICE FORDHAM, BYLINE: The story begins in White Sands National Park, an ethereal landscape in southern New Mexico where waves of white gypsum dunes lap across a vast basin. That basin held a lake during the last ice age, and on its dried-out banks lie thousands of fossil footprints of mammoths, giant sloths and humans. In 2021, researchers from the park service, the U.S. Geological Survey and others published a paper in the journal Science saying those footprints were between 21,000 and 23,000 years old, and that was controversial.
KATHLEEN SPRINGER: These ages were really much older than sort of the accepted paradigm of when humans entered North America.
FORDHAM: Kathleen Springer is one of the U.S. Geological Survey researchers. She says scientists had thought humans might have crossed from what's now Siberia to Alaska at the end of the last Ice Age as glaciers retreated. Maybe that was wrong. And if it was...
SPRINGER: It opens up whole avenues of migratory pathways. How did people get here?
FORDHAM: But critics challenged the research. Some said the dating technique used was flawed. It tested seeds from water plants embedded along with the footprints. But those plants can absorb older carbon from water, skewing the results. So after some pandemic delays, the researchers returned to the trench, this time to carbon-date tree pollen for better accuracy. Also, they took samples of the lakebed.
SPRINGER: They're like tubes pounded in the sedimentary sequence and taken back to a laboratory and analyzed.
FORDHAM: For those samples, they used a different technique that looks at the luminescent properties inside quartz crystals, which change with age. Today a new paper is out with results from both tests, and the scientists say they confirm their original findings. Jeff Pigati also from the U.S. Geological Survey, hopes it'll close the case.
JEFF PIGATI: People can argue against any single dating technique, but it's the totality of the study, the congruence of the ages from all three different dating techniques that really make our results exceptionally robust.
FORDHAM: Well, not so fast, says Loren Davis, professor of anthropology at Oregon State University, who co-authored that critical paper last year. He does think the new research is important, but...
LOREN DAVIS: I unfortunately don't share their conclusions that they have resolved the issue of timing of when people were making these footprints.
FORDHAM: He says the samples of quartz came from the very lower deposit of the study area and that the possible age range is broad.
DAVIS: All they really are telling us is that the clay that underlies all the footprints is potentially as young as 16,000 and potentially older than 21,000. That's pretty uncertain.
FORDHAM: The debate is sure to continue, but other sites that might be older than 14,000 years are starting to get more attention, too.
EDWARD JOLIE: Things are changing extremely rapidly.
FORDHAM: Edward Jolie is a professor of anthropology at the University of Arizona who worked on the footprints project.
JOLIE: What's exciting about the White Sands discoveries is that they really kind of force us again to entertain this notion that significant parts of what we thought we knew or understood are in need of some serious revision.
FORDHAM: Jolie is of Oglala Lakota and Hodulgee Muscogee heritage. He says technology is transforming his field. And another thing is that more Indigenous people are involved in research into these early Americans. He says new voices are asking different questions and moving toward new answers. For NPR News, I'm Alice Fordham in Santa Fe, N.M.
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