Ancient Footprints Show Humans Arrived in the Americas During the Ice Age


The ancient human footprints preserved at the site across from New Mexico’s White Sands National Park are surprisingly old. scientists have reported On Thursday, it dates back to the Ice Age, about 23,000 years ago.

The results, if they continued to study, would revive the scientific debate about how humans first spread to the Americas, implying that they did so at a time when massive glaciers covered most of their path.

Arguing for such an early arrival, the researchers hailed the new study as conclusive evidence.

“I think this is probably America’s greatest discovery in a hundred years,” said Ciprian Ardelean, an archaeologist at the Autonomous University of Zacatecas in Mexico who was not involved in the study. “I don’t know what gods they’re praying to, but it’s a dream invention.”

For decades, many archaeologists have argued that humans only spread to North and South America at the end of the last ice age. They noted the earliest known tools dating to around 13,000 years ago, including spearheads, scrapers, and needles. The technology was known as Clovis for the town of Clovis, NM, where some of these early instruments originated.

The age of the Clovis instruments was neatly ordered by the retreat of the glaciers. This alignment supported a scenario where Siberian hunter-gatherers moved to Alaska during the Ice Age and lived on for generations until ice-free corridors opened up and allowed them to expand southward.

Beginning in the 1970s, however, some archaeologists began publishing ancient evidence of humanity’s presence in North America. Last year, Dr. Ardelean and colleagues published a paper. report Stone tools from 26,000 years ago in a mountain cave in Mexico.

Other experts are skeptical of such ancient finds. Some of these supposed tools may actually be oddly shaped rocks, said Ben Potter, an archaeologist at the Center for Arctic Studies at Liaocheng University in China. Dr. Potter also questioned some of the dates the scientists assigned to their findings. For example, if an instrument sinks into the sediment underneath, it may appear older than it actually is.

Dr. “Each of them has unresolved issues,” Potter said of the allegedly older sites. “None is certain.”

The work at White Sands now adds a new set of evidence for an early arrival: Instead of tools, the researchers found footprints.

The footprints were first discovered in 2009 by the park’s resource program manager, David Bustos. Over the years, he has brought in an international team of scientists to help make sense of the findings.

Together, they found thousands of human footprints on the park’s 80,000 acres. A path was made by someone walking in a straight line for a mile and a half. Another shows a mother laying her baby down. Other pieces were made by children.

“Children tend to be more energetic,” said Sally Reynolds, a paleontologist at the University of Bournemouth in England and co-author of the new study. “They’re a lot more fun, jumping up and down.”

The evidence that humans left footprints is “conclusive”, said Mathew Stewart, a zooarchaeologist at the Max Planck Institute for Chemical Ecology in Jena, Germany, who was not involved in the study.

The footprints were created when people strode across the moist, sandy ground at the edge of a lake. Later, the deposits gently filled the prints and the ground hardened. But subsequent erosion re-emerged the pressures. In some cases, impressions are only visible when the ground is unusually wet or dry – otherwise they are invisible to the naked eye. But ground-penetrating radar can reveal three-dimensional structures, including heels and toes.

Mammoths, fearsome wolves, camels and other animals also left their footprints. A series of fingerprints showed that a giant sloth was in close company, avoiding a group of humans.

Dr. “The fascinating thing about examining footprints is that they provide snapshots in a timely manner,” Stewart said.

The job of determining the age of the prints fell to Jeffrey Pigati and Kathleen Springer, two research geologists of the United States Geological Survey.

In 2019 they went to White Sands to get a feel for the site. Wandering around some of the footprints, the researchers came across ancient ditch seeds that sometimes grow near the lake. At some points, the abundant seeds formed thick blankets.

The researchers brought some seeds back to their lab and measured the carbon in them to determine their age. The results were shocking: Trench grass had grown thousands of years before the end of the last ice age.

Dr. Pigati and Ms. Springer knew these numbers would be controversial. Thus, they embarked on a much more ambitious work. Dr. “The darts will start flying, so we better be ready for them,” Pigati recalled.

The scientists dug a trench near a group of human and animal footprints to more precisely estimate their age. Next to the trench, they could see layer by layer of sediment. By carefully mapping the surrounding ground, they were able to trace the footprints of humans and animals up to six layers in the ditch interspersed with eleven seedbeds.

The researchers collected ditch seeds from each bed and measured their carbon. These measurements confirmed the initial results: The earliest footprints at the site – left by an adult human and a mammoth – were placed under a seedbed from around 22,800 years ago.

In other words, the people who left their footprints walked around White Sands about 10,000 years before the Clovis people. Researchers estimate that the youngest footprints date from about 21,130 years ago. This meant that people lived or regularly visited the lake for about 2,000 years.

“It’s a bomb,” said Ruth Gruhn, an archaeologist at the University of Alberta who was not involved in the study. “At first glance, it’s very difficult to refute.”

Dr. Potter commended the White Sands team for their care in the new study, saying it was the strongest case ever made for people in the Americas before 16,000 years ago. But he said he would have felt more confident in the extraordinary age of prints if there was other evidence beyond the ditch seeds. The seeds may have absorbed old carbon from the lake water, making them look older than they really are.

“I want to see stronger data and I don’t know if it’s possible to get stronger data from this site,” he said. “If that’s true, then it really has some profound implications.”

If humans settled well in New Mexico 23,000 years ago, they must have started spreading long before Alaska. Bournemouth University’s Dr. “It starts turning back time,” Reynolds said.

Some researchers have argued that humans may have spread to the Americas even when the glaciers were at their peak. Instead of traveling on the mainland, could move along the shore. Alternatively, Dr. Ardelean and colleagues hypothesized that humans traveled inland more than 32,000 years ago, before Ice Age glaciers reached their maximum size and blocked that path.

Dr. Gruhn argued that both scenarios are possible in light of new evidence from White Sands. More work is needed to find older sites that favor one over the other. “We have a lot of work to do,” he said.

There is more research planned by Mr. Bustos and his colleagues at White Sands. They want to learn about the behavior of the people who left their footprints there. Did they hunt animals around them? Did they live on the lake permanently or just visit?

They should work fast. The erosion that exposes the footprints will wipe them out of the landscape in a few months or years. Countless footprints disappear before scientists see them.

“This is a little heartbreaking,” said Mr. Bustos. “We’re racing to try to document what we can do.”


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