'Ghost Fossils' Show Early Human Activity in North America Before the End of Last Ice Age

When David Bustos initially traveled to White Sands National Park in New Mexico to work as a wildlife biologist in 2005, he heard about the "ghost trails." The phantom footsteps would emerge on the otherwise blank soil when the ground was wet enough at certain periods of the year, only to vanish when it dried out.

Ghost Tracks

Scientists didn't confirm the ghost tracks were created by actual humans until 2016, more than a decade later - and it's only now that some of the ancient footprints at White Sands have been dated as of the earliest in North America.

"We had been skeptical of the age for a long time, and now that we have it, it's fascinating," Bustos said. "One of the cool things is that mammoth prints can be seen in the strata a meter or so above the human footprints, which adds to the overall story."

"Earliest Known Human Activity in the Americas"

The footprints at White Sands were dated by analyzing the seeds of Ruppia cirrhosa, also known as ditchgrass, an aquatic plant that formerly thrived along the edges of the dried-up lake. According to a study co-authored by Bustos and published Thursday in the journal Science, the ancient ditchgrass seeds were discovered in layers of hard ground both above and below the many human footprints at the site. They were radiocarbon-dated to estimate their age.

The traces discovered in one site are the earliest known footprints and the oldest definite evidence of humans anywhere in the Americas, indicating that people were there 21,000 to 23,000 years ago - thousands of years earlier than experts previously thought.

The study's principal author, Matthew Bennett, a professor of environmental and geographic sciences at Bournemouth University in the United Kingdom, stated, "It's the oldest clear evidence for people in the Americas."

Related Article: Prehistoric Evidence Shows Mammals Evolved Rapidly When Dinosaurs Went Extinct 

Fossilized Human Footprints

Fossilized human footprints have already been discovered along the national park's east side, where the bed of a now-dry "paleo-lake" supplies the gypsum-rich soil that is eroded by the wind to form the region's famed white dunes.

According to Bennett, any evidence of early human occupation has been questioned since it depended on what appeared to be natural stone tools or artifacts that had migrated from their original stratigraphic levels.

Other evidence of early people in the Americas would gain credence as a result of the footprints.

Studying the Last Glacial Maximums

Whether people arrived in the Americas through a northern route from Siberia before or after the Last Glacial Maximum when enormous ice sheets rendered migration down the Pacific Coast or across western Canada impossible has long been contested. According to Bennett, the ancient footprints in White Sands answer this issue, indicating that they arrived up to 30,000 years ago, thousands of years before the ice period peaked.

The footprints were produced in a lush marsh populated by mammoths, ground sloths, bovids - cattle - and wild camels, as well as the Stone Age people who hunted them.

According to Cornell University archaeologist Thomas Urban, a co-author of the study, the footprints mixed in with animal traces suggest that humanity must have lived there for at least 2,000 years.

Foot Print Diversity

Urban pioneered the noninvasive use of ground-penetrating radar to detect footprints beneath the surface and identify researchers with the ideal excavation sites.

According to Urban, teenagers and youngsters leave smaller footprints than adults, presumably because they are engaged in things that require easy labor rather than specialized occupations such as hunting.

Studying Footprints

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 study, said it was difficult to date when fossilized footprints were made, especially when they were pressed into layers of mud rather than more easily dated volcanic ash, as they were at White Sands.

She wrote in an email that it's "amazing to see that this team was able to restrict the date of the footprint creation using radiocarbon dates from the [layers] above and below."

Unlike bones or artifacts, Footprints preserve fossilized activity, and their examination can provide information about the printmakers.

"Human footprints offer us with a window into the life of our forefathers and, in this case, extensive information on their daily activities and social dynamics," Liutkus-Pierce added.

Also Read: 5 Most Important Fossil Discoveries in the World

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