First Humans Came To North America Thousands Of Years Earlier Than Previously Thought
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The first humans arrived in North America between 21,000 to 23,000 years ago. This was thousands of years earlier than what was previously thought. A September 2021 study conducted by researchers from the US Geological Survey and other international researchers made this discovery after analysing ancient human footprints found in White Sands National Park in New Mexico. Now, a new study, which is a follow-up research to the previous one, has confirmed the finding that the first humans reached North America during the time of the Last Glacial Maximum, which occurred about 20,000 years ago during the last phase of the Pleistocene epoch, implying that humans went to North America thousands of years earlier than what was once thought.
The study describing the findings was recently published in the journal Science.
The finding implies that early humans and megafauna (huge animals) co-existed for several millions of years before the terminal Pleistocene extinction event, which was marked by the extinction of many genera of large mammals, including mammoths, ground sloths, and beavers. Compared to other continents, the extinction event was the most distinct in North America, where 32 genera of large animals disappeared in a short duration of 2000 years.
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As part of the new study, researchers used two new independent approaches to determine the age of the footprints. Both ways showed the same results.
When the 2021 study was published, there was a lot of dissent throughout the scientific community on the accuracy of the findings.
The original ages, or the ages determined as part of the 2021 study, were obtained by radiocarbon dating. Initially, the researchers determined the age by dating seeds of the aquatic plant Ruppia cirrhosa. This plant was found in the fossilised impressions of the footprints.
However, since aquatic plants can obtain carbon from dissolved carbon atoms in the water rather than ambient air, the measured ages could turn out to be older than the actual ages.
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What new techniques were used to date the footprints?
As part of the follow-up study, the researchers performed radiocarbon dating of conifer pollen. This is because conifer pollen belongs to terrestrial plants, and hence, does not give rise to the problems that arose when dating Ruppia.
The researchers isolated about 75,000 pollen grains for each sample they dated. In a statement released by the USGS, David Wahl, a co-author on the new paper, said that the pollen in samples came from plants which are found in cold and wet glacial conditions, unlike present-day conifer pollen which are found in dry regions.
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The researchers used another technique to date the footprints. This technique is called optically stimulated luminescence. Using this method, one can date the last time quartz grains were exposed to sunlight. This technique also found that the quartz samples collected within the footprint-bearing layers had a minimum age of about 21,500 years.
Therefore, there are three separate lines of evidence that show that the first humans arrived in North America about 21,000 to 23,000 years ago.
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