Tuesday , October 26 2021

Fossil footprints show humans inhabited the Americas thousands of years earlier than we thought



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Our species began migrating out of Africa about 100,000 years ago. Apart from Antarctica, the Americas were the last continents to be reached by humans, with the first pioneers crossing the already submerged Bering Earth Bridge, which formerly connected eastern Siberia with North America.

At times throughout the Pleistocene ice age, which ended 10,000 years ago, large layers of ice covered much of Europe and North America. The water enclosed in these layers of ice lowered the sea level, allowing people to walk across the bridge from Asia across the Arctic to Alaska. But during the peak of the last glacial cycle, its path south to the Americas was blocked by a layer of continental-wide ice.

Until now, scientists believed that humans were only traveling south to the Americas when this ice barrier began to melt, at most 16,500 years ago. But together with our colleagues, we have discovered a set of fossil footprints that suggest that humans first set foot on the continent thousands of years earlier. These footprints, unearthed in White Sands National Park in New Mexico, were made by a group of teenagers, children and occasionally adults and have been dated to the height of the last glacial maximum, about 23,000 years ago. This makes them potentially the oldest evidence of our species in the Americas.

Our findings support the idea that humans were present in southern North America before the last glacial peak, a theory that has so far been based on controversial and potentially unreliable evidence.

Step change There are tens of thousands of fossil footprints in White Sands. Together they tell stories of how prehistoric humans interacted with extinct glacial-era megafauna, such as Colombian mammoths and terrestrial lazy people. The tracks were deposited around the edges of a large wetland, perhaps a lake after the rainy season, but at other times it looks more like a mosaic of bodies of water. Until now, the problem had been dating these footprints. We knew they were printed before the megafauna became extinct, but not exactly when.

That changed in September 2019 when the team found tracks with intact sediments above and below. Within this sediment were layers containing hundreds of seeds of the common ditch grass Ruppia cirrhosa. These seeds, when dated with radiocarbon, would reveal the age of the footprints themselves. The analysis revealed that the seeds range from 21,000 to 23,000 years old, suggesting that humans made repeated visits to the site for at least two millennia. The footprints of White Sands provide unequivocal evidence that people were in the Americas at the height of the last glacial maximum, rather than some time later, as previously thought. This is important for our understanding of the population of the Americas and the genetic makeup of Native Americans.

Using the DNA of modern Native Americans, scientists have discovered that their ancestors came from Asia in several waves, some of which were genetically isolated. The cause of this isolation is unclear. Now, our new footprint evidence is explained, suggesting that the early Americans were isolated south of the American ice sheet, to join the others when it melted.

Our discovery may also reopen speculation about other archaeological sites in the Americas. One of them is the Chiquihuite cave in Mexico. Recently, archaeologists claimed that evidence from this cave suggests that humans occupied the Americas about 30,000 years ago, 7,000 years before people left footprints of white sand.

But the findings of the Chiquihuite Cave are disputed by some, as stone tools can be difficult to interpret and tool-like stones can be formed through natural processes. Stone tools can also move between layers of sediment and rock. Fossil footprints cannot. They are fixed in a bed plan and therefore provide more reliable evidence of when humans left them.

Teen Kicks We tend to imagine our ancestors engaged in death or life struggles, forced to fight the elements simply to survive. Still, the White Sands rehearsals suggest a playful and relatively relaxed environment, with teens and kids spending time together as a group.

Maybe it’s not that surprising. Children and teens are more energetic and playful than adults and therefore leave more footprints. Adults tend to be cheaper in their movement, leaving less trace. But another interpretation of this new evidence is that teenagers were part of the workforce in these early hunter-gatherer bands. It is possible for young people to leave their footprints looking for and transporting resources for their prehistoric parents.

In any case, the people who left their footprints in White Sands were some of the oldest known American teenagers. Placed in stone, their footprints pay homage to their ancestors, who we now know traveled the long land bridge to American millennia before it was commonly believed.

(This story has not been edited by Devdiscourse staff and is automatically generated from a syndicated feed.)

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