Ancient footprints found at the Site of New Mexico. These footprints date between 21,000 and 23,000 and may belong to children and adolescents.
White Sand National Park in southern New Mexico is famous for its chalky sand dunes that stretch for hundreds of square kilometers. But at the peak of the last ice age, the area was wetter and the meadows were more lush. Mammoths, giant sloths and other animals walk on the muddy shores of shallow lakes that increase or decrease with the seasons. They have companions.
In a landmark study published Sept. 23 in a journal, researchers noted that human footprints on an ancient lakeshore in the park date back between 21,000 and 23,000 years. If the chronology is accurate — experts say it is likely — the fingerprints represent the earliest definitive evidence of human occupation anywhere in the Americas.
"The evidence is very convincing and very exciting," said Tom Higham, an archaeologist and radiocarbon dating expert at the University of Vienna. "I am sure that these footprints are indeed the same age as claimed."
The dates raise questions about when and how Siberians settled in the region, with growing evidence that Siberians bypass the Pacific coast while inland routes are mired in ice. The study's authors say the footprints corroborate controversial evidence that the Americas showed signs of settlement earlier.
Spencer Lucas, a paleontologist at the Museum of Natural History and Science in New Mexico, Albuquerque, said: "This paper makes a very compelling case that these footprints are not only human, but that they are over 20,000 years old. ”
Rock evidence
For decades, archaeologists have associated the earliest Americans with stone spear tips from 11,000-13,000 years ago and other remains of the "Clovis" culture (named after another New Mexico site, but found throughout North America). These dates coincide with the decline of a continent-sized glacier that forms an ice-free corridor through central Canada.
The discovery of numerous "former Clovis" archaeological sites from Alaska to the tip of South America, dating back to 16,000 years ago, has raised questions about the "Clovis first" hypothesis and provided a basis for migration routes from the Siberian coast.
Research journals are dotted with even earlier websites, including a controversial paper that placed humans in California 130,000 years ago. But many of these claims have been discounted because of uncertainty in the evidence: rocks may have been mistaken for tools, and traces on animal bones could have been caused by natural processes — or, in California's version, by diggers — rather than slaughter.
Excavations in Baisha National Park uncovered a human footprint at the bottom of a ditch.
The white sands are strewn with fossil footprints of humans and animals — in 2018, the same team that found these footprints in the latest paper documented an attempt to hunt giant sloths on a dry lake bed known as playa. But the age of these footprints is notoriously difficult to determine, says study co-author Matthew Bennett, an earth scientist at the University of Bournemouth in the United Kingdom who specializes in fossil footprints. "Every time you find something, it's probably a different era."
Ancient Seeds
In 2019, study co-author David Bustos, an archaeologist and resource manager at White Sands, discovered a site on a beach where traces went directly into layers of rocky hard sediment. The rock contains the seeds of an aquatic plant, Ruppia cirrhosa, which can be dated with carbon dating. Bennett said: "This is the holy grail for dating footprints. ”。
When researchers at the U.S. Geological Survey in Denver, Colorado, determined that the seeds were dated between 21,000 and 23,000 years, he and his colleagues were not surprised because a previous small-scale excavation had dated the sediments to about the same time. But Bennett said the team knew that claims of human occupation at this age would be of great concern.
So they try to address factors that can distort seed age. The most likely phenomenon is that the organism combines carbon from nearby rocks, such as calcium carbonate in limestone, filtered into the water. These carbon sources tend to be much older than carbon in Earth's atmosphere.
The researchers say this "reservoir effect" is unlikely to occur. They dated hundreds of seeds in different sedimentary layers, with their ages consistent, with older seeds at the bottom and younger seeds at the top. Daniel Odes, an archaeologist at the National Park Service in Washington, D.C., says there could be more variation if the seeds contain old carbon. In a site in the region without any footprint, the seeds of spiral gutter grass are the same age as the same layer of charcoal – this is not affected by the reservoir.
Thomas Stafford, an experimental geronologist at stafford Research Laboratory in Lafayette, Colorado, said, "I really think these ages are OK. ”。 He noted that even 1,000-year-old mistakes do not tarnish the importance of these footprints. Stafford added: "Whether it was 20,000 years ago, 22,000 years ago or 19,000 years ago, people here are not going to change their incredible story. "We have human footprints."
Teen Footprints
The team determined that these dozens of footprints may belong to many people, most of them children and adolescents. "It makes a lot of sense to me," Odes said, "and when I was younger, I always went into the water. Streams, rivers, ponds, whatever it is. If given the chance, I might walk in the mud instead of on dry ground. ”
Karen Moreno is a paleontologist at the University of Chile in Southern Valdivia, and there is no doubt that these footprints are human. She also doesn't believe the photos were mostly made by children, as the estimates are based on the height of modern people. But those footprints, she said, could illuminate America's earliest humans. "This ancient community is likely to have a different and complex way of life."
Now that there is strong evidence that humans settled in the Americas more than 20,000 years ago, Bennett said, researchers should work to address the consequences. He hopes the footprints of white sand will force researchers to reconsider sites with more ambiguous evidence of early human occupation.
David Meltzer, an archaeologist at Southern Methodist University in Dallas, Texas, is convinced of the footprints of the white sand, but disagrees with the footprints to make the more controversial site credible. However, Melzer added that the discovery of stone tools or other artifacts would help forge such a link.
Hayham said the footprints made it "highly likely" that the ancestors of the White Sands and other early settlers traveled along the Pacific coast. He added that the next step will be to identify the people who have arrived through these ice age voyages. "An urgent research focus is not only on finding such footprints, but also on the remains of the people who made them."