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By Michael Haederle

When U.S. Geological Survey (USGS) scientists Jeff Pigati and Kathleen Springer and their colleagues first publicized their excavation on the shore of an ancient lakebed in White Sands National Park in southern New Mexico’s Tularosa Basin, they expected some blowback.

Their 2021 paper reported finding dozens of fossilized human footprints—some belonging to children or teenagers—that were laid down along the muddy shoreline. Aquatic plant seeds found adjacent to the footprints yielded radiocarbon dates of between 21,000 and 23,000 years B.P. (before present).

It was a startling finding that pushed back the long-accepted chronology of the arrival of people in the Americas by thousands of years.

Skeptics wasted no time weighing in. In a 2022 rebuttal in Science, critics pointed out that the aquatic plants, which absorb all of their carbon from water, might have picked up old carbon from groundwater—a phenomenon known to return radiocarbon dates for samples that are thousands of years older than they really are. The authors suggested the White Sands researchers use optically stimulated luminescence to date the materials.

Researcher Nicholas Kessler images tree rings with “Skippy,” a robotic camera system.

In October 2023, the White Sands team published an expanded study in Science doing just that. In addition to the dating of the seeds, they now included radiocarbon dating of pollen from conifer trees, which obtain their carbon from the air via photosynthesis. And they used the optical luminescence method to date tiny grains of quartz from the layers of sediment in which the footprints were found. All three approaches converged on the same date range.

“If the seed ages and the pollen ages and the luminescence ages all agree, it’s case closed,” Pigati said matter-of-factly. “We can stop arguing about this, because there’s nothing that can make all three of these converge, yet still be wrong.”

Whether it’s truly case closed may still be debated, but the White Sands research stands as a textbook example of how contemporary scientists are using an array of sophisticated dating techniques to gain new insights into the past—and sometimes settle disagreements.

Yet the application of scientific dating methods isn’t always straightforward. It’s the marriage of many disciplines that requires considerable technical expertise, with results often leaving ample room for interpretation. And that inevitably shapes the stories archaeologists tell.

This is an article excerpt from the Winter 2023 edition of American Archaeology Magazine.  Become a member of The Archaeological Conservancy for your complimentary subscription!