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A new study on the fossilized human footprints at White Sands National Park challenges previous theories of when humans have arrived in the Americas. Wildlife scientist David Bustos said that he first heard about these "ghost tracks" that appear when the ground is wet and disappear when it dried out in 2005, NBC reported.

It was not until 2016 that scientists have confirmed that the tracks were made by real people when massive ice sheets are believed to have blocked human migration to the Americas.

 Fossilized Footprints From 21,000 Years Ago Fuels New Speculation When Humans Arrived in the Americas
(Photo: Wikimedia Commons)
2100-year-old human footprints preserved in volcanic mud near the lake in Managua, Nicaragua. They are called Huellas de Acahualinca.

Earliest Evidence of Humans in North America

According to an article in Nature, White Sands National Park, in southern New Mexico, was once wetter and grassier where aquatic plants thrived along the shore and Mammoths, giant sloths, and other animals used to live.

Researchers of the study, titled "Evidence of Humans in North America During the Last Glacial Maximum" published in Science, used radiocarbon dating on the seeds of an aquatic plant that lived in White Sands National Park to determine their age. They found the seeds in layers of hard Earth near the fossilized human footprints at the site.

As NBC reported, the team identified the tracks as the earliest known footprints and the oldest evidence of humans arriving in the Americas, particularly North America. Radiocarbon dating revealed that the tracks dated from 21,000 to 23,000 years ago, which scientists once believed several thousands of years.

Matthew Bennett, the lead author of the study from Bournemouth University in the UK, said that finding a footprint in the site is a certain data point. The study has established the importance of the site as the area where the ancient humans in North America once lived.

"You can now look at the oldest sites and say, 'We know they were there during the Last Glacial Maximum,' so maybe some of these oldest sites are also reliable," NBC quoted Bennett.

Other archaeologists agree on the evidence that these fossilized footprints are from humans and genuinely are from the age radiocarbon dating detected. However, this questions when and how humans from Siberia have crossed the Pacific coast while being blocked by massive ice, preventing human migration.

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Last Glacial Maximum

According to National Geographic, the Last Glacial Maximum spanned from 20,000 to 26,500 years ago, wherein temperatures decreased and glaciers locked up an increasing volume of water that sent sea levels plummeting. A pair of massive ice sheets called Laurentide and Cordilleran formed a continuous icy wall from the Atlantic to the Pacific that may have made human migration at that time impossible.

Due to that, scientists in the mid-1900s have argued that humans first started arriving in the Americas 13,000 years ago with the rise of the Clovis culture. But in recent times, scientists accepted the idea that humans may have arrived 17,000 years ago and traveled along the Pacific coast that became passable before the icy continent melted.

With the recent discovery in the White Sands that proved they were human footprints, archaeologists said that humans may have arrived in the Americas earlier than 20,000 years ago. They pointed out that they not only found a single layer of fossilized footprints, but they found several of them.

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Check out more news and information on Archaeology in Science Times.