' The Sands Of Time ' : New tests on footprints bolster claims about early humans' arrival in America.

Hidden in White Sands National Park in New Mexico are human footprints that a paper published in 2021 said could have been made as early as 21,000 to 23,000 years ago, some of the oldest evidence yet found of people in the Americas.

That claim elicited calls for more tests, and now a new study published in the journal Science adds to the evidence for those dates.

The 2021 study relied on analysis of seeds from an aquatic grass, and some scientists noted that such grass sometimes produces murky radiocarbon results. So for the latest study, the team took two new tacks.

Researchers analyzed carbon isotopes in ancient pollen grains, a process that showed they had been deposited on a verdant landscape, cooler than today's, as would be expected in that period.

And they determined the date of a layer of the White Sands sediments using a process called optically stimulated luminescence, which reveals how long quartz sand has been beneath the surface.

'' We've got seed ages, we've got pollen ages, we've got luminescence ages - they all converge, '' said Jeff Pigati, a geologist at the U.S. Geological Survey and a study co-author.

'' They all agree, and it's really tough to argue against that.'' [Maya Wei-Haas]


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