More evidence of an earlier arrival…

Ancient Footprints Push Back Date of Human Arrival in the Americas

Human footprints found in New Mexico are about 23,000 years old, a study reported, suggesting that people may have arrived long before the Ice Age’s glaciers melted.

Fossilized human footprints that a White Sands National Park program manager first discovered.
Fossilized human footprints that a White Sands National Park program manager first discovered.Credit…Dan Odess
Carl Zimmer

By Carl ZimmerSept. 23, 2021Updated 2:22 p.m. ETSign up for Science Times  Get stories that capture the wonders of nature, the cosmos and the human body. Get it sent to your inbox.

Ancient human footprints preserved in the ground across the White Sands National Park in New Mexico are astonishingly old, scientists reported on Thursday, dating back about 23,000 years to the Ice Age.

The results, if they hold up to scrutiny, would rejuvenate the scientific debate about how humans first spread across the Americas, implying that they did so at a time when massive glaciers covered much of their path.

Researchers who have argued for such an early arrival hailed the new study as firm proof.

“I think this is probably the biggest discovery about the peopling of America in a hundred years,” said Ciprian Ardelean, an archaeologist at Autonomous University of Zacatecas in Mexico who was not involved in the work. “I don’t know what gods they prayed to, but this is a dream find.”

For decades, many archaeologists have maintained that humans spread across North and South America only at the end of the last ice age. They pointed to the oldest known tools, including spear tips, scrapers and needles, dating back about 13,000 years. The technology was known as Clovis, named for the town of Clovis, N.M., where some of these first instruments came to light.

The age of the Clovis tools lined up neatly with the retreat of the glaciers. That alignment bolstered a scenario in which Siberian hunter-gatherers moved into Alaska during the Ice Age, where they lived for generations until ice-free corridors opened and allowed them to expand southward.

But starting in the 1970s, some archaeologists began publishing older evidence of humanity’s presence in North America. Last year, Dr. Ardelean and his colleagues published a report of stone tools in a mountain cave in Mexico dating back 26,000 years.

Other experts have been skeptical of such ancient finds. Ben Potter, an archaeologist at the Arctic Studies Center at Liaocheng University in China, said that some of these supposed tools might actually be oddly shaped rocks. Dr. Potter also questioned some of the dates scientists have assigned to their finds. If a tool sinks into underlying sediment, for example, it may appear to be older than it really is.

“There are unresolved issues with every single one of them,” Dr. Potter said of the older purported sites. “None of them are unequivocal.”

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

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

Together, they have found thousands of human footprints across 80,000 acres of the park. One path was made by someone walking in a straight line for a mile and a half. Another shows a mother setting her baby down on the ground. Other tracks were made by children.

Researchers work on excavating a footprint in the bottom of a trench.
Researchers work on excavating a footprint in the bottom of a trench.Credit…Dan Odess

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

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

The footprints were formed when people strode over damp, sandy ground on the margin of a lake. Later, sediments gently filled in the prints, and the ground hardened. But subsequent erosion resurfaced the prints. In some cases, the 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 their three-dimensional structure, including the heels and toes.

Mammoths, dire wolves, camels and other animals left footprints as well. One set of prints showed a giant sloth avoiding a group of people, demonstrating that they were in close company.

“What is fascinating about the study of footprints is that they present snapshots in time,” Dr. Stewart said.

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

In 2019, they went to White Sands to get a feel for the site. Walking around some of the footprints, the researchers sometimes came across ancient seeds of ditch grass that had grown by the lake. In some spots, the abundant seeds formed thick blankets.

The researchers brought some of the seeds back to their lab and measured the carbon in them to determine their age. The results came as a shock: The ditch grass had grown thousands of years before the end of the last ice age.

Dr. Pigati and Ms. Springer knew those numbers would be controversial. So they embarked on a far more ambitious study. “The darts are going to start flying, so we better be ready for them,” Dr. Pigati recalled.

The scientists dug a trench near one cluster of human and animal footprints to get a tighter estimate of their age. On the side of the trench, they could see layer after layer of sediment. Carefully mapping the surrounding ground, they were able to trace the footprints of humans and animals to six layers in the trench, interspersed with eleven seed beds.

The researchers collected ditch grass seeds from each bed and measured their carbon. These measurements confirmed the initial results: The oldest footprints at the site — left by an adult human and a mammoth — were located below a seed bed dating back about 22,800 years.

In other words, the people who left the footprints walked around White Sands about 10,000 years before the Clovis people. The youngest footprints, the researchers estimated, dated to about 21,130 years ago. That meant that people lived or regularly visited the lake for about 2,000 years.

Ancient ditch grass seeds were used to date the footprints.
Ancient ditch grass seeds were used to date the footprints.Credit…David Bustos

“This is a bombshell,” said Ruth Gruhn, an archaeologist at the University of Alberta who was not involved in the study. “On the face of it, it’s very hard to disprove.”

Dr. Potter praised the White Sands team for their care in the new study, saying that it is the strongest case yet made for people in the Americas before 16,000 years ago. But he would feel more confident in the extraordinary age of the prints, he said, if there were other lines of evidence beyond the ditch grass seeds. The seeds could have absorbed older carbon from the lake water, making them seem older than they really are.

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

If humans were well established in New Mexico 23,000 years ago, they must have started spreading down from Alaska long before that. “That starts to wind back the clock,” said Dr. Reynolds of Bournemouth University.

Some researchers have argued that people could have spread through the Americas even when the glaciers were at their peak. Instead of traveling down the mainland, they could have moved along the coast. Alternatively, Dr. Ardelean and his colleagues have proposed that people traveled inland more than 32,000 years ago, before Ice Age glaciers reached their maximum extent and blocked off that route.

Dr. Gruhn argued that both scenarios remained possible in light of the new evidence from White Sands. It would take more work to find earlier sites that favored one of them over the other. “We’ve got a lot to do,” she said.

Mr. Bustos and his colleagues have more investigations planned at White Sands. They want to learn about the behavior of the people who left their footprints there. Did they hunt the animals around them? Did they live permanently at the lake or just pay it visits?

They must work quickly. The erosion that has revealed the footprints will erase them from the landscape in a matter of months or years. Countless footprints are disappearing before the scientists even lay eyes on them.

“It’s kind of heartbreaking,” Mr. Bustos said. “We’re racing to try to document what we can.”

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The genetic plot thickens

When the Kennewick Man was discovered in Washington State a great argument ensued. Native tribes demanded that the bones remain with them, as an honored ancestor of 9,000 years ago. Others – non-Natives – argued the Kennewick Man carried “Western” traits (whatever the heck that means) and might have origins from Europe. A battle ensued. Along the way, of course, DNA analysis and genetic testing has evolved rapidly, such that today there are complete genomes of ancient peoples available from both the Old and New World. Recently, as the article below describes in fascinating detail, Kennewick Man has been confirmed as a true Native American ancestor, and his remains returned. It is still the strong belief, supported by evidence, that Native American peoples came from Eurasia, mainly Siberia, some 15,000 to 24,000 years ago. We have already forgotten that just two decades ago the STRONG belief was that nobody was in the Americas until the “Clovis” people appeared 12,000 years ago. As every year passes, dramatic rethinking is being forced by new finds:

  • Ancient people reached the Americas at least 20,000 years ago, and maybe much earlier;
  • Ancient peoples understood maritime seafaring and wandered widely, but during a time when sea levels were much lower such that all their sites are now covered;
  • Ancient patterns of trade and resource exchange were complex and widespread, often covering thousands of miles;
  • All during human development the climate has changed, some times rapidly, in enormous swings, equally as dramatic then as the current concerns about global warming have people panicking today;
  • There is now a begrudging acceptance that humans living in the time of the great animals were, for thousands of years, NOT the top predator, but barely able to linger in out of the way protected sites.

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Razor stone…

I built this theory that during the last ice age, thousands of years, even tens of thousands of years before the accepted time of crossing the land bridge ( less than 15,000 years ago), people might have been in the Americas, living along the coast, sheltering on islands in glacial refugia away from the great carnivorous animals and near fish and marine mammals for food. Because, then, people must have been few in number, and because even in our earliest days humans knew it was healthiest to find mates not directly related to family members, I think it is fair to guess that bands of raiders went out and sought to steal people from other groups. This behavior has often been documented even in recent memory, as for example knowledge that First Peoples from way north in British Columbia sailed their great canoes south to the Strait of Juan de Fuca to capture women and slaves from Puget Sound tribes living along the shores of the strait.

Evidence exists that ancient people were tremendous seafarers, surely able to leave the sight of land for fish, for travel, and while a coastline in an ice age might have long sections bounded by cliffs of ice, I speculate travel was possible, and frequent. The structure of the ice age world revealed in the Strong Heart Series is, of course, fiction, but as true as I could make it based on the research I did. It seemed to me then, and still does, it would be a lot easier to have other people capture and steal mates from inland neighbors if you could offer something of tremendous value in exchange. In my stories, I imagined that these ancient People walked south across the Great River for razor stone – they crossed the Columbia for the obsidian available in Oregon – and then they headed toward the Bering land bridge with this razor stone to trade for wives at a meeting place somewhere midway along that land bridge.

Of course this idea contradicts accepted theory on every level – my tales took place not 12,000 years ago nearly 70,000 years ago – I suggest people could navigate their great canoes 2,000 miles along an exposed coast and survive, I argue that because of the great animals humans barely survived in out of the way and hard to reach refuges, protected by ice, by water; that humans lived and even thrived all this time along the strip of shore now buried hundreds of feet beneath a rising ocean.

This tale came to me in 2012, or the first draft did, and I thought, then, God has a sense of humor, a wicked one, and as sure as I am writing this today, at some time in the near future something will be found confirming that humans have been in the Americas far longer than 15,000, or even 20,000 or 40,000 years. It better be a damn good find because everyone with careers built the current thesis will fight to the death to protect that thesis, as even now some still fight to protect the 12,000 year “Clovis” thesis, which was debunked by the finding of a spear point in a mastodon bone in Sequim, Washington that is 13,800 years old – the oldest evidence of hunting, I think, anywhere in the Americas.

But, that razor stone, and the idea a people collected that stone for use in trade for wives with other people living far, FAR away, beyond the land bridge, was not when my story first appeared ridiculous to me, and now may be even more reasonable based on the report that obsidian – razor stone – only available in Oregon, has now been found under Lake Huron, at least 9,000 years old. The age of this find fits within current dogma about the end of the ice age, but also shows that people, even back just as the ice was melting, traded materials over thousands of miles.

We know so little….

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Ancient Humans Thought Experiment (1)

It seems we now have fossil evidence of at least 6500 individuals from ancient times; that is, older than, say, 10,000 years, and much of this evidence has appeared in the last 20 to 30 years. There is today a revolution taking place in the study of human origins. New technologies, new methods of dating, the ability to retrieve DNA from ancient bones and even from the dirt over which ancient people lived, is announced on a monthly basis, and as the new finds are reported new theories arise, are defended, some times accepted. We know today that there were several different types of ancient humans coexisting together and that these different types interbred and produced offspring. We know, for example, that many of us contain Neanderthal DNA, or Denisovian DNA. Yet, while the fossil record may reflect 6500 individuals, there are only about 200 fossil skulls that have been found, which suggests that, given all the effort and energy expended searching for human origins, the evidence is still very sparse.

There is another debate that occurs, as well, concerning when these ancient humans became “modern,” whatever that means. It seems that some versions of ancient humans were as large as humans today, with a brain case as large or larger than today, extending back at least 600,000 years. Yet evidence for modern behavior – burial of the dead, artwork, sculpture, sophisticated tool kits and technology – is generally agreed to only extend back into the past 70,000 years, although sites in Africa much older show red ochre as a possible decoration. This raises the question – what happened, then, that enabled humans to develop culture, technology, community as we understand it today; what was the incident or event that caused a being with a certain brain size and structure to suddenly begin leaving behind evidence of myth, dreams, narrative, and history?

It is agreed that hominids arose in Africa, and extended from Africa to the rest of the world, maybe in a couple of migrations, the first being Homo Erectus almost two million years ago and a latter migration much later about the same time as modern humans appeared. But the evidence is contested. Some argue the first modern humans were found in northeast Africa, others say the Middle East, there is even a find in eastern China that may be older still. There seems to be general agreement that humans crossed the sea to reach Australia 80,000 years ago, and it is also generally accepted that the western hemisphere, North and South America, was empty of hominids until the end of the most recent ice age when some humans crossed the Bering Land bridge and entered North America, either along the coast or inland once some ice had melted. There are disagreements about this, of course, with some arguing humans made it to the Americas about 14,000 years ago and others arguing humans arrived much earlier. There is a site in the Yukon, Old Crow, that may be 24,000 years old. A few argue that humans came to the Americas far earlier than that. However, there are hardly any archeological finds older than 14,000 years to support such an argument.

For decades the belief was that humans crossed the Land Bridge, then waited for a channel to melt in the two great ice sheets covering Canada, then raced south to fill the continent, killing all the great animals on the way. More recently another argument has emerged, arguing that humans first made it to the Americas by traveling the coast in boats or canoes, beach to beach or island to island, living off the marine resources and bypassing those places where the ice sheets met the sea. One big challenge with this thesis is that during the ice ages the sea level was as much as 330 feet below present day sea level, meaning any coastal communities or evidence lies buried beneath tons of water. The beach scene pictured above, Olympic National Park in northwestern Washington State, which is probably what that ancient shore looked like tens of thousands of years ago, was, back during the ice time, on a slope hundreds of feet above the beach below it.

We now know that ancient humans were capable of using boats or canoes and fishing offshore, and moving island to island. In Timor evidence of tuna fishing was found, 40,000 years old, and to catch such tuna one needs to travel beyond the sight of land.

Two factors seem to be missing from all these arguments, at least in the research I have done. The first applies to the animals among which these humans lived, and how their presence and behavior might have influenced human decisions and choices as to places to shelter. The second concerns the relationship between human behavior and movement and the frequent ice ages that swept across the top half of the world – one every 100,000 years for at least two million years.

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