Human evolution: aging footprints in New Mexico (Introduction)

by David Turell , Thursday, July 04, 2024, 16:29 (142 days ago) @ David Turell

At 22,000+ years ago;

https://www.sciencenews.org/article/human-footprints-new-mexico-ancient-dating

"Human footprints in White Sands National Park in New Mexico sparked controversy two years ago when scientists found the prints to be surprisingly old, dating to about 22,000 years ago. Now, two other ways of dating the fossilized tracks converge at similar ages as the first estimate, potentially resolving the dispute, researchers report in the Oct. 6 Science.

'The finding adds to mounting evidence that humans arrived in North America thousands of years earlier than previously thought.

***

"In 2021, researchers described more than 60 footprints embedded in what was once mud alongside an ancient lake in what’s now New Mexico. Radiocarbon dating of an aquatic plant’s seeds in and around the footprints — which span several rock layers — suggested that people roamed there for two millennia between roughly 23,000 and 21,000 years ago (SN: 9/23/21). The result added to other evidence pushing back on a long-held theory that the first humans in North America came from Siberia via a land bridge sometime around 16,000 to 14,000 years ago.

"But some scientists noted that the aquatic plants used to date the footprints could have absorbed ancient carbon in groundwater, a well-known phenomenon. “There’s a potential then for the plant to give exaggerated perspectives on its age,” says Davis, who cowrote a critique of the 2021 paper.

"The criticism wasn’t surprising, says geologist Jeff Pigati of the U.S. Geological Survey’s Geosciences and Environmental Change Science Center in Denver. “We knew from the very beginning that we were going to have to independently evaluate the ages with different dating techniques.”

"To add to their past work, Pigati and colleagues radiocarbon-dated pollen stuck in the same layers as some of the footprints. The pollen came from land plants, primarily pine, spruce and fir trees, avoiding the groundwater carbon issue. The researchers also collected quartz grains above the lowest footprints and used a dating method that estimates how long the quartz had been buried.

"The pollen yielded an age range of roughly 23,400 to 22,600 years old, and the quartz gave an age minimum of about 21,500 years old. Both results echo the previous age estimate.

***

"Despite possible errors in the individual dating methods, “the data overall from the [new] study strongly indicate human presence in the Americas” around 22,000 years ago, Bente Philippsen, a physicist at the Norwegian University of Science and Technology in Trondheim, wrote in a commentary in the same issue of Science."

Comment: there have been some reports of earlier human activity in South America.