A hunter-gatherer who trekked through a desert oasis a hundred centuries ago left the continent’s most lasting impression: the oldest known human footprints in North America.
There are only two of them — one left and one right — but the ancient traveler’s path through mineral-rich sediment in the Chihuahuan Desert allowed them to become enshrined in stone, and now dated, some 10,500 years later.
“To my knowledge the oldest human prints previously reported in North America are around 6,000 years old, so the … prints pre-date these by some 5,000 years,” said Dr. Nicholas Felstead, a geoarchaeologist at Durham University who led a new analysis of the prints.
The tracks were first discovered during highway construction in northeastern Mexico, about 300 kilometers from the Texas border, in 1961. They were excavated and taken to a local museum for study, but their precise location was lost to history.
A search for the site in 2006 came up empty, but it did turn up an additional 11 tracks in the general area where the original prints were believed to have been found — a marshy, spring-fed desert refuge known as Cuatro Ciénegas.
Felstead and his team were able to date the tracks because they were preserved in travertine, a sedimentary rock that contains minute traces of uranium from the waters in which it formed.“Both sets of prints are ones that have been identified before and are the only reported footprints in the Cuatro Ciénegas Basin, but neither have previously been dated,” Felstead said in an interview.
Since uranium decays into the element thorium at predictable rates, the scientists were able to measure the ratio of those materials to determine the specimens’ ages.
Their results showed that the pair of tracks discovered in 1961, now housed at Saltillo’s Museo del Desierto, were about 10,550 years old.
The 11 other prints, which remain where they were found in a Cuatro Ciénegas quarry, dated back about 7,250 years, according to the research.