When Experts Scoured Below The Sand With Radar, They Found Ancient Footprints That Rewrite History

Researchers are surveying ground in New Mexico’s White Sands National Monument. To do this, they’re using an established technology for a novel purpose. The scientists are scanning the surface of an area called Alkali Flat with ground-penetrating radar (GPR). And what they now discover below this ancient dried-out lake bed gives them some startling new insights into humans and animals from 12,000 years ago.

In 2019 the archeologists were working on the eastern section of Alkali Flat. This area once lay beneath water, which is now known as Lake Otero. This lake once covered most of what is known as the Tularosa Basin – a large, enclosed depression which collected water. During the time of the last Ice Age, this water gradually soaked into the ground and it left behind the dried lake bed.

That arid lake bed forms what is now known as the Alkali Flat, and the scientists were exploring an 800-meter section of that. With the use of GPR technology they were able to “see” beneath the ground without actually having to dig and potentially disturb the very evidence that they wanted to analyze.

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The GPR machinery allowed the researchers to look back through time to an era some 12,000 years ago when the last Ice Age glaciation was coming to an end. What they were looking for – with more than a little success – were traces known as “ghost tracks” of life from that ancient era. And that included human life as well as evidence of large, long-extinct animals.

We’ll see exactly what the archeologists found shortly, but first let’s learn a little more about the geology and history of the White Sands National Monument. We’ll take the story back to the Permian Period – a geological era that started around 299 million years ago when the previous period, the Carboniferous, ended.

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The Permian lasted for about 47 million years and during that time the White Sands area was at the bottom of shallow seas. As those ancient waters shrank and dried out, they left behind them deposits of calcium sulfate – which is better known as gypsum. Gypsum is now used as a fertilizer and for the manufacture of products such as drywall and blackboard chalk.

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The lands revealed by the disappearing sea were elevated by the movement of tectonic plates around 70 million years ago. In time, these came to form the San Andres and Sacramento Mountains. About 30 million years ago, the tectonic activity formed the Tularosa Basin. Rainfall eroded the relatively soft gypsum in the mountainous sections of the area and the material was then washed into the basin. And that’s where our researchers were working in 2019.

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The rainwater that poured down from the mountains into the Tularosa Basin had nowhere to go except into the ground, because the basin feature has no outlet. Once it had soaked into the old seabed with its deposits of gypsum, forming occasional pools, a material called selenite was left behind. Selenite, for its part, is simply gypsum in a crystalline state.

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These selenite crystals that cover the Alkali Flat and lie around the dried-out lake bed come in all shapes and sizes and can be as large as three feet across. However, over time erosion has broken down most of the selenite crystals to form the white sands that give the area its name. The prevailing winds pile these sands up into the impressive dunes that the region is famous for.

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In fact, these selenite sand dunes, formed from gypsum, are rather unusual. Gypsum is a relatively common mineral, but because it readily dissolves in water, most of it ends up being swept into rivers and on into the sea. However, as we’ve seen, the Tularosa Basin has no outlets to rivers or the sea, so the selenite stays in situ.

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The white sands of New Mexico with their strange dune formations extend for some 275 square miles. The dunes that we see today were likely formed between 6,500 and 7,000 years ago, and wind action can see them moving as much as 30 feet in a single year. About 40 percent of the extent of the sands lies within the White Sands National Monument – which is looked after by the U.S. National Park Service.

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As far as we know, humans first came to the White Sands area at the end of the last Ice Age glaciation around 12,000 ago. They would have found the shores of Lake Otero in the Tularosa Basin which had not yet dried up. In fact, the environment would have been very different from today – because of the presence of water.

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The terrain around Lake Otero was grassland which provided a habitat for many animals, including large mammals such as giant sloths, mammoths, camels and bison. Paloeindian people, probably nomadic hunters, traveled across the land and would have hunted for game there. Unfortunately, we know little about these humans, because they left behind scant archeological traces.

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But we do know that these Stone Age Americans were skilful tool makers because of artifacts that have been discovered. These Paleoindians fashioned stones gathered from the mountains that surround the Tularosa Basin into elaborate spearheads. These would have made effective spears for hunting the game attracted by the waters of Lake Otero and the surrounding pastures.

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These first people to occupy what would become New Mexico in the distant future were around for some 2,000 years. At that point, Lake Otero would have started to dry out. This changed the local environment and ended the previous abundance of pasture and the large animals which grazed it. As a result, the humans residing there had to modify their ways of living if they were to survive.

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The end of the Paleoindian culture, hastened by the desertification of the White Sands, led to the next era of human occupation known as the Archaic Period. Since the big game was now gone, hunting alone was not enough to support a population and around 8,000 years ago the people now became hunter-gatherers.

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As time went by, the Archaic people of White Sands began to form links with tribes in adjacent areas and even started trading with them. There was also an increasing tendency for people to form settled communities often near water sources. This led to a new era which historians call the Jornado Mogollon, and it started around 1,800 years ago.

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Early on in this next period, people began to make pottery and build dwellings which were semi-permanent or even permanent. The people who had previously been hunter gatherers began to turn instead towards settled living and the cultivation of crops. They probably grew beans, squash and corn while still hunting animals and collecting wild plants and herbs.

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Some historians are of the view that these Mogollon people were engaged in trading with others who lived as far away as the Pacific coast. Today, the Mogollon are known for their particular types of ceramics and for the pit houses and the pueblos that they built. For reasons that remain unclear, the Mogollons then disappeared from the scene around 700 years ago.

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As far as it known, after the Mogollons left White Sands there was a period when the area was not occupied by any humans. However, in around 1450 A.D. or perhaps somewhat earlier, Apachean people appeared on the scene. The ancestors of these people had traveled southwards from western Canada and Alaska over the years.

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The Apache people built seasonal dwellings in the White Sands area and lived there undisturbed until around the middle of the 19th century. There were some expeditions by Spanish explorers in search of gold before then, however. One party, for example, was led by Cabeza de Vaca but they found none of the yellow metal. The only legacy the Spanish left was horses and cattle that became feral.

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New Mexico became U.S. territory in 1848 following the Mexican-American War. Then around two years later European and Hispanic ranchers began moving into the Tularosa Basin area. At that time there were still fertile grasslands, although overgrazing had eradicated those by the end of the 19th century.

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The Tularosa area now had a feel of the Wild West with disputes often settled by gunfights. Such desperadoes as William McCarty, better known as Billy the Kid, were on the loose. There were also conflicts between the Europeans and the earlier settlers, the Apaches who had been living in Tularosa for some four centuries. Then in 1873 the Mescalero Indian Reservation was instituted.

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In 1933, recognizing the special environmental status of the gypsum sand dunes, President Herbert Hoover ordered the establishment of the White Sands National Monument. Then World War II brought dramatic changes to the Tularosa Basin; part of it became the Alamogordo Bombing and Gunnery Range. A military airport, today called the Holloman Air Force Base, was also established.

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The military also set up what is now called the White Sands Missile Range in the Tularosa Basin. July 16, 1945 saw a momentous event at the Missile Range. That was the day that the world’s first atomic bomb was detonated. After the end of WWII more missiles and bombs were tested at the site and it was also used for military pilot training.

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Now, the White Sands National Monument – living side by side with the military facilities – is a major tourist destination. The site is visited by nearly half-a-million people each year, who are keen to experience Tularosa’s beguiling scenery. But it’s not just tourists who are fascinated by this strange environment. Archeologists are also drawn to the White Sands in search of knowledge about the people who occupied it thousands of years ago.

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There have indeed been some intriguing finds at the Tularosa Basin’s Alkali Flat site. David Bustos, a park naturalist with White Sands, discovered a set of footprints known as a trackway in 2008. And in a press release from the National Parks Service ten years later, Bustos described why this particular trackway was of such interest to scientists.

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“The thing that is special about these prints and sets them apart from any other fossil trackways in the world is that this discovery records the interaction between humans and Ice Age giant megafauna,” Bustos explained. He continued, “White Sands National Monument has the largest concentration of human and Ice Age giant megafauna prints in the Americas.”

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The animal that the humans were apparently interacting with in these tracks was a giant sloth. These formidable animals could grow to be 20 feet from their heads to their tails and weighed in at considerably more than four tons. That means they were around the size of a modern African elephant. And the tracks seem to show that the humans were hunting this formidable beast some 12,000 years ago – likely armed with nothing more than primitive spears.

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In 2018 scientists analyzed in detail the tracks originally found by Bustos a decade earlier. Those tracks were the 20-inch footprints of the giant sloths – which became extinct many thousands of years ago. But within the sloths prints were the unmistakable tracks of human feet. It seems that the humans were deliberately stepping in the tracks left by the sloths.

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To step into the tracks, these ancient people would have had to vary their normal stride – lengthening it so as to match that of the larger sloth. The pattern of the prints implies that the humans were deliberately stalking the giant sloth, presumably regarding it as potential prey. These prints were the first time that evidence of a likely giant sloth hunt had ever been found.

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And it sounds like hunting a giant sloth was no picnic in the park. The paper the researchers published in 2018, Footprints preserve terminal Pleistocene hunt? Human-sloth interactions in North America gives a description of how it likely unfolded. Although couched in academic language, the explanation of it vividly illustrates the dangers faced by hunters some 10,000 years ago.

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The researchers wrote, “… The circular sloth trackways are consistent with defensive behaviors in which sloths reared on their hind-limbs, freeing their forelimbs for defense. We termed these structures ‘flailing circles.’” And don’t forget, this creature fighting for its life could have been up to 20 feet long and more than four tons in weight.

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Research team leader Matthew Bennett told the Science Alert website in 2018 that, “These were fearsome animals. They had claws like Wolverine. I wouldn’t have wanted to go head-to-head with one. It would be a very silly risk to take.” But such were the dangers of life on the White Sands faced by these brave Paleoindians.

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After that 2018 discovery the research team, this time led by Thomas Urban of Cornell University, returned to the Alkali Flat site for further investigations. But this time the scientists were trying out a new research technique, ground-penetrating radar (GPR). The use of this technology meant that they could scan the ground for ancient footprints without having to dig into the earth – potentially destroying valuable evidence.

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In fact, GPR is hardly a new technology. A patent for a machine to detect objects underground using radar waves was first issued in 1910. But the technology really took off in the 1970s and it’s been used by scientists in researching groundwater, ice and soils. Engineers use it to detect utility wires and pipes. Furthermore, in recent years, archeologists have discovered how useful it can be in their research of underground artifacts.

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GPR works by emitting an electro-magnetic pulse into the ground which is then reflected back to a receiver. The returned signal can then be read and gives an accurate view of unseen objects – or indeed footprints – under the surface. And what the researchers found at Alkali Flat in 2019 was more exciting evidence of the interaction between man and the animals that lived around him thousands of years ago.

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In this latest season of research, the team discovered human footprints walking a distance of 2,625 feet. But what they also found were the prints made by a Columbian mammoth. And what’s more, the tracks of the human and this beast crossed over. Indeed, one such print had a human foot print inside it. Was this evidence of a Paleoindian stalking the mammoth as potential prey?

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Hunting can’t be ruled out as a possibility, but Urban said that the appearance of the mammoth and human footprints crossing was actually much more likely to have been coincidence. He explained to the National Post in November 2019 that the tracks in fact showed that the mammoth had crossed the human tracks at a 90-degree angle. When the human had returned along his pathway, he had then crossed the mammoth’s route.

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So it seems that on this occasion, the archeologists had not found evidence of humans hunting the large mammals that shared this part of what is now New Mexico with them. Nevertheless, this concrete evidence that early settlers in North America were sharing the land with mammoths is exciting enough on its own. And Urban hopes that the use of GPR will reveal more fascinating evidence from the ancient past.

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