23,000-year-old footprints suggest people reached the Americas early

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Footprints left in layers of soil and silt in New Mexico’s White Sands National Park may be between 23,000 and 21,000 years old. It is based on radiocarbon dating of the remains of grass seeds buried in layers of sediment above and below the track. If the dates are correct, the tracks are evidence that people migrated along the now-dry Lake Otero during the height of the last ice age, when kilometers of ice covered the northern part of the continent. And that would mean that people would have arrived in North America—and made their way to an area well south of the ice—before the ice sheets expanded enough to close the route.

reaching beyond the ice sheets

Bournemouth University archaeologist Matthew Bennett and his colleagues found a total of 61 human footprints east of an area called Alkali Flats, which was once an ancient lake bed and shoreline. Over time, as the lakebed expanded and shrunk with changes in climate, it left behind varying layers of clay, silt, and sand. Seven of those layers, recently excavated by Bennett and his colleagues in the area, lay human tracks with long-lost megafauna.


Some layers of sediment contained the remains of ancient grass seeds mixed with the sediment. Bennett and his colleagues radiocarbon dated from the layer just below the oldest footprints and just above the most recent ones. According to the results, the oldest footprints were made sometime after 23,000 years ago; The most recent ones were created sometime around 21,000 years ago. At that time, the northern part of the continent was several kilometers below vast ice sheets.

The ice sheets in most of Canada and North America were completely covered by about 26,000 years ago, and they would not begin to melt and shrink until about 20,000 years ago.

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“These data provide definitive evidence of human occupation of North America south of the Laurentide ice sheet during the Last Glacial Maximum,” Bennett and colleagues wrote in their recent paper. And anyone who lived in what is now New Mexico during this period, known as the Last Glacial Maximum, must have migrated from Asia to the Americas before the ice sheets closed.

If so, we may need to rethink the role of our species in the extinction of megafauna such as mammoths and giant ground sloths. “It also raises the possibility of a human role in megafauna extinctions previously thought to have predicted their arrival,” Bennett and colleagues wrote.

the discovery of the first americans

North and South America were the last continents that humans reached; As far as we know, our other hominin relatives never came here. At the moment, the oldest widely accepted evidence of people in the Americas comes from a scattering of sites along the western coasts of both continents, and is 13,000 to 16,000 years old.

Our understanding of how and when people entered America has changed significantly in recent years. Until about a decade ago, it seemed that the first Americans were part of the Clovis culture, named for the distinctive projectile points left near what is now Clovis, New Mexico. All available evidence indicates that the Clovis people made their way south through a corridor that opened in the middle of the ice sheets about 13,000 years ago.

But then, as is usually the case (at least on a good day), archaeologists found new evidence, such as a 14,000-year-old footprint in Argentina, a 14,600-year-old footprint in Chile, 14,500 Years Old – Older sites in Florida, and stone tools dating back 16,000 years in western Idaho. That evidence pushed back the date of arrival by a few thousand years, suggesting that the Clovis people were not actually the first to arrive. It also saw the first Americans actually cut the edge of the ice sheets along the Pacific coast.

At the moment, most evidence suggests that people arrived in North America about 16,000 years ago and followed the coast to the south of the ice sheets. However, if Bennett and his colleagues are right, the recently discovered tracks at White Sands could substantially change what we think we know again. 23,000-year-old footprints can only mean that people were already living in New Mexico before ice sheets closed the southern part of the continent from the rest of the world for the next few thousand years . It is possible – even likely – another wave of new ones will arrive as the ice sheets recede, but there may already be someone here to meet them.

Evidence for Extraordinary Claims

Extraordinary claims require extraordinary evidence, as the late astronomer Carl Sagan would say. And Bennett and his colleagues are certainly making an extraordinary claim. If there is going to be a scientific debate about the White Sands Track, it is likely to be centered on the dating of the sedimentary layers involved.

Seed mixed in the layers above and below the tracks of white sand provided an easy way to date the tracks. But aquatic plants, such as the type of grass that Bennett and his colleagues dated, can sometimes look older than their own. If the water is full of dissolved calcium carbonate from very old diatoms or other aquatic life, this can lead to a very low carbon-14 ratio in plants. it’s called a hard water effect (or reservoir effect).

To examine their results, Bennett and his colleagues compared radiocarbon dates from terrestrial and aquatic plants in the vicinity of the Alkaline Flat. Aquatic dates correspond to terrestrial ones, meaning that aquatic plants that grew in the region for several thousand years probably did not suffer from harsh water impacts.

The new claim is also less far-fetched, and some are supported by much stronger evidence than others. For example, a group of archaeologists in California insisted that they found a 130,000-year-old mammoth-butcher site that would house humans in California, before we had any evidence that our species also made it from Africa to Europe. was made as. And the case of the improbably old California site depends entirely on whether some of the round stones were used as hammers.

Meanwhile, the 23,000-year-old tracks in the White Sands appear to match up nicely with a paper published last year, in which stone tools were discovered from a 30,000-year-old sediment layer in a cave in Mexico. is described.

ice age works

If people were moving around in New Mexico during the Last Glacial Maximum, who were they and what were they doing? Most of the people who leave the track at White Sands appear to be teenagers and children. This is based on what the measurements of his feet tell us about his height. If this is true, they may be fetching water or gathering food or other resources.

“One hypothesis for this is the division of labor, in which adults are involved in skilled tasks while adolescents are tasked with ‘fetch and carry.’ Children accompany the adolescents,” Bennett and colleagues wrote.

It also seems that most children had more flat feet than most people living today, which suggests that they often walked barefoot. The paws of the tracks seem to be slightly stretched, which usually happens when someone slips while walking, such as on a muddy pond.

The environment of the White Sands was perfect for preserving footprints for thousands of years. Last year, the same team of researchers found a 10,000- to 15,000-year-old track of a teenager or young woman traversing vast and vast ground sloths while carrying a small child. In 2019, he used radar to find the hidden track. And in 2018, they tracked the footsteps of predators chasing giant sloths.

Science, 2021 DOI: https:/10.1126/science.abg7586; (About DOI)

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