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hubie [soylentnews.org] writes:

The age claim of the preserved footprints found in New Mexico's Lake Otero Basin are brought into question [dri.edu]:

The wide expanse of an ancient lakebed in New Mexico holds the preserved footprints of life that roamed millennia ago. Giant sloths and mammoths left their mark, and alongside them, signs of our human ancestors. Research published in September 2021 claimed that these footprints are "definitive evidence of human occupation of North America" during the last ice age, dating back to between 23 and 21 thousand years ago. Now, a new study [cambridge.org] disputes the evidence of such an early age.

[...] At the center of the debate are the tiny seeds of an aquatic plant used to age the footprints. The timeframe for the seeds was identified using radiocarbon dating methods, in which researchers examine a type of carbon known as Carbon-14. Carbon-14 originates in the atmosphere and is absorbed by plants through photosynthesis. [...] But the plant species used, Ruppia cirrhosa, grows underwater and therefore obtains much of its carbon for photosynthesis not directly from the atmosphere as terrestrial plants do, but from dissolved carbon atoms in the water.

"While the researchers recognize the problem, they underestimate the basic biology of the plant," says Rhode. "For the most part, it's using the carbon it finds in the lake waters. And in most cases, that means it's taking in carbon from sources other than the contemporary atmosphere – sources which are usually pretty old."

[...] The authors demonstrated this effect by examining Ruppia plant material with a known age from the same region. Botanists collected living Ruppia plants from a nearby spring-fed pond in 1947 and archived them at the University of New Mexico herbarium. Using the same radiocarbon dating method, the plants that were alive in 1947 returned a radiocarbon date suggesting they were about 7400 years old, an offset resulting from the use of ancient groundwater by the plant. The authors note that if the ages of the Ruppia seeds dated from the human footprints were also offset by roughly 7400 years, their real age would be between 15 and 13 thousand years old – a date which aligns with ages of several other known early North American archaeological sites.

The dating of the footprints can be resolved through other methods, including radiocarbon dating of terrestrial plants (which use atmospheric carbon and not carbon from groundwater) and optically stimulated luminescence dating of quartz found in the sediment, the authors write.

Previously: Fossilized Footprints Show Humans Made It to North America Much Earlier Than First Thought [soylentnews.org]

Journal Reference:
Charles G. Oviatt et al., A critical assessment of claims that human footprints in the Lake Otero basin, New Mexico date to the Last Glacial Maximum, Quat Res, 2022. DOI: 10.1017/qua.2022.38 [doi.org]

Original Submission