Prehistoric traces cast doubt on the time of settlement of America by people

Scientists have obtained evidence that people arrived in America much earlier than previously thought. When the discovery of fossilized footprints from what is now New Mexico was made public in 2021, it caused a sensation in archeology, seemingly rewriting a chapter of human history. Now a new study offers further evidence of their significance.

Although they look like they could have been made yesterday, the prehistoric footprints were pressed into the mud 21,000 to 23,000 years ago, according to radiocarbon dating of aquatic plant seeds preserved above and below the fossils.

According to CNN, this date dramatically pushes back the chronology of human history on the American continent, the last landmass to be inhabited by prehistoric humans. The 61 dated prints, which were discovered in the Tularosa Basin, near the edge of an ancient lake in White Sands National Park, were made at a time when many scientists believe massive ice sheets blocked human passage to North America, indicating that people arrived in the region even earlier.

However, some archaeologists have questioned the age of the tracks suggested by these initial finds. Skeptics noted that aquatic plants such as Ruppia cirrhosa, which was featured in the 2021 study, may obtain carbon from dissolved atoms in the water rather than from the air, which could lead to an erroneously early date.

In a follow-up study published Thursday in the journal Science, the researchers said they presented two new lines of evidence to support their original dates.

“Even as the original work was published, we moved forward to validate our results with a wealth of evidence,” said Kathleen Springer, a research geologist at the USGS and co-author of the new scientific paper. “We were confident in our original age, as well as in the compelling geological, hydrological and stratigraphic evidence, but we knew that independent chronological control was critical.”

When and how early humans first migrated to the Americas has long been debated and remains poorly understood. Current estimates of the number of the first inhabitants range from 13,000 to more than 20,000 years ago. However, the earliest archaeological evidence for occupation of the region is sparse and often contradictory, making the traces especially important.

In their follow-up study, the researchers focused on radiocarbon dating conifer pollen because it comes from terrestrial plants and avoids problems that can arise when dating aquatic plants such as ruppia, the press release said.

Scientists were able to isolate about 75 thousand pollen particles, collected from the same layers as the original seeds, for each sample. Thousands of grains are required to obtain the mass required for a single radiocarbon measurement. The age of the pollen corresponded to the age of the seeds.

The team also used a dating technique known as optically stimulated luminescence, which determines when the quartz grains in the fossil sediment were last exposed to sunlight. This method assumed that the minimum age of the quartz was 21,500 years.

“The immediate reaction in some quarters of the archaeological community was that the precision of our dating was not sufficient to make the extraordinary claim that humans were present in North America during the Last Glacial Maximum,” said Jeff Pigati, a USGS geologist and one of the lead authors of the study. “But our focused methodology in this current study really paid off.”

This research helps shed light on the grand story of human evolution, but much remains unknown about how North and South America were populated, CNN notes. It is unclear whether the ancient people arrived by boat or by land bridge from Asia. Also, despite advances in genetic data, it is unclear whether one or many populations of early modern humans made this long journey.

Bente Philippsen, associate professor and radiocarbon dating expert at the Norwegian University of Science and Technology, said dating pollen particles is “a complex process with a risk of contamination.”

Moreover, she noted in a commentary published along with the study, dates derived from luminescence have a large measurement error.

However, she said the new study’s findings overall “strongly indicate” human presence in the Americas around the time of the Last Glacial Maximum, a period between 19,000 and 26,000 years ago when two massive ice sheets covered the northern third of North America. extending south to New York City, Cincinnati and Des Moines, Iowa.

Ice and cold temperatures would have made travel between Asia and Alaska impossible during this time, meaning the people who left the tracks likely arrived much earlier.

Jennifer Ruff, an assistant professor at the University of Kansas and author of Origins: A Genetic History of the Americas, said the fingerprint findings were a “big deal” for the field.

“The American continents were the last step in the global journey of modern people around the world,” she notes. “It’s interesting to imagine what it would have been like to enter a new region and face the challenges (and opportunities) that would present new conditions.”