Date confirmation of 23,000-year-old footprints in the United States

About 23,000 years ago, in what is now New Mexico, a group of hunter-gatherers walked around a lake surrounded by cones and sagebrush, leaving traces of where they had gone in the mud. . These bare footprints, Described in the journal in 2021 Science, now etched into rock in the White Gypsum Desert of White Sands National Park. In a new study published Friday, Oct. 6, in the same journal, Matthew Bennett (Bournemouth University, United Kingdom) and his colleagues confirmed their seniority based on two new dating techniques.

Since the discovery was announced, this antiquity has been the subject of intense debate. These traces actually call into question one of the archeological theories of the New World, according to which it could not have been occupied by man until 13,500 years ago, the period attested by the so-called “Clovis” culture. Spear-shaped stone points. According to this theory, Paleo-Indians would have set foot in the Americas from Asia via the Bering Strait, which was considered impassable during the last glacial maximum (- 26,500 years ago – 19,000 years ago).

The white sand footprints contradict this view of events. Early dating was criticized based on the study of spiral rubies mixed with carbon 14 footprints in the seeds of an aquatic plant. Carbon-14 dating actually decays as these plants absorb inorganic carbon dissolved in the water they bathe in. This carbon may have an old appearance, which distorts the measurement. Aware of the possible source of this error, Matthew Bennett and his team also took care to sample fossil pollen that was not sensitive to this “reservoir effect.” They took 75,000 pollen grains each from three samples and obtained carbon-14 dates between 23,400 and 22,600 years ago.

But, for greater security, they relied on a third dating called “optically induced luminescence.” This is based on the fact that minerals such as quartz, when isolated from sunlight, become charged depending on the radiation received from the surrounding environment. This counter is reset to zero when these crystals are illuminated or heated. By measuring the fluorescence signal they emit when stimulated with monochromatic light, we can estimate how long they have been buried. Quartz from the white sand gave a date of 21,500 years (give or take 2,000 years).

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