Science

Fossil footprints show humans in North America more than 21,000 years ago

The tracks at one location have been revealed as both the earliest known footprints and the oldest firm evidence of humans anywhere in the Americas, showing that people lived there between 21,000 and 23,000 years ago — several thousand years earlier than scientists once  believed.

“It’s the earliest unequivocal evidence for humans in the Americas,” said Matthew Bennett, a professor of environmental and geographic sciences at Bournemouth University in the  United Kingdom and the lead author of the study.

Fossilized human footprints have now been found throughout the east of the national park, where the bed of a “paleo-lake,” which is now dry, supplies the gypsum-rich earth that’s eroded by the wind to create the enormous white dunes for which the region is famous.

Any traces of early human habitation had been disputed because they relied on what seemed to be stone tools that might have formed naturally, Bennett said, or on artifacts that might have moved from their original stratigraphic layers.

The team has studied the footprints at White Sands National Park for years, following the tracks with ground-penetrating radar and excavating trenches.NPS, USGS and Bournemouth University

“A footprint is a really good, unequivocal data point,” he said. “That’s the importance of this site — we know they were there.”

The footprints would in turn give greater credibility to other evidence of early humans in the Americas. 

“You can now look at the oldest sites and say, ‘We know they were there during the Last Glacial Maximum,’ so maybe some of these oldest sites are also reliable,” he said.

The term “Last Glacial Maximum,” or LGM, is how scientists refer to the height of the last ice age, roughly between 20,000 and 26,000 years ago.

It’s long been debated if humans first arrived in the Americas via a northern route from Siberia either before or after the Last Glacial Maximum, when vast sheets of ice would have made migration along the Pacific Coast or through western Canada impossible.

The ancient footprints at White Sands now answer that question, suggesting they may have arrived up to 30,000 years ago, thousands of years before the height of the ice age, Bennett said.

The location of the new excavations was the shore of a wetland when the footprints were made between 21,000 and 23,000 years ago.Karen Carr

Although White Sands is now mostly a desert, it was a lush wetland at the time the footprints were made and populated by mammoths, ground sloths, bovids — cattle — and wild camels, as well as by the Stone Age humans  who hunted them.

The footprints are intermingled with the tracks of the animals, and show that people must have lived there for at least 2,000 years, Cornell University archaeologist Thomas Urban, a co-author of the research, said in an email.

“There are multiple footprint layers spanning a significant amount of time, suggesting a sustained human presence in the area during the Last Glacial Maximum, as opposed to a single event,” he said.

Urban developed the noninvasive use of ground-penetrating radar to reveal the footprints beneath the surface and show the researchers the best places to excavate.

Smaller footprints made by teenagers and children outnumber those made by adults, Urban said, possibly because they were involved in tasks that involved simple labor, instead of skilled tasks like hunting.

“Their presence is simply part of ordinary life and should be expected,” he said. Their activities may have ranged from playing to chores such as gathering food, water, and raw materials for their hunter-gatherer community.

Geologist Cynthia Liutkus-Pierce of Appalachian State University in North Carolina, who has studied ancient human footprints in Tanzania but was not involved in the White Sands research, said it was often difficult to date just when fossilized footprints were made, especially when they were pressed into layers of mud — as at White Sands — and not into more easily dated volcanic ash.

“[It’s] great to see that this team was able to constrain the date of the footprint formation using radiocarbon dates from the [layers] above and below,” she said in an email.

Unlike bones or artifacts, footprints are unique in that they recorded fossilized behavior, and their analysis can yield clues about the printmakers.

“Human footprints give us a glimpse into the lives of our ancestors and, in this case, provide detailed information on their day-to-day activities and social dynamics,” Liutkus-Pierce said.


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