Dozens of ancient footprints have been found along the shores of American Ice Lake. It has now been proven once and for all that humans have been in North America for much longer than previously thought. Although the original discovery caused a lot of controversy, its subsequent study was even more difficult.
Two years ago, scientists concluded that immortal footprints in the mud of New Mexico’s White Sands National Park were more than 21,000 years old. The result was inconsistent with prevailing theories about how the first humans migrated to the Americas, and a heated debate erupted over the legitimacy of the method — carbon dating of plant seeds, found in footprints — that was used to determine it. Age to determine footprints.
Last Glacial Maximum
The scientists United States Geological Survey (USGS) He took the criticism to heart have to work to gather additional evidence for their claim through two new methods. “The reaction of some of the archeological community is that the accuracy of our date is not sufficient to support the serious claim that humans were present on the North American continent during the last glacial maximum — the time when most of the water on Earth was stored as ice. . . . This was 20,000 to 22,000 years ago. We began to look for additional evidence. The new study described Our approach has been tremendously successful,” said USGS Geologist Jeff Picati.
Carbon uptake by aquatic plants
Controversy surrounded the accuracy of the original age estimates obtained by radiocarbon dating. It contained the seeds of a common aquatic plant Ruppia cirrhosa analysed, they were found in fossil footprints. The problem is that aquatic plants absorb their carbon atoms not only from the surrounding air, but also from water. Hence the age measured may have been too high.
“When we presented our original study two years ago, we were already working to find additional evidence for our results by coming to the same conclusion in other ways,” said researcher Kathleen Springer. “We were confident in our original age estimates and strong geologic, hydrological, and stratigraphic evidence. But we knew that independent chronological verification was critical.
Prehistoric pollen
In a follow-up study, the researchers focused on carbon dating of pollen grains from cones, since it is a land plant. This way there are no questions about the origin and age of carbon atoms, as in aquatic plants. The team made no effort to isolate the 75,000 pollen grains for each sample they dated. The pollen grains were taken from the same layer of soil as the original seeds of the aquatic plants, so they could be compared with each other. In all cases, the age of the pollen grains was similar to the age of the original seeds.
“The pollen samples helped us understand the wider environment at the time the footprints were formed,” explains researcher David Wall. “Pollen grains from our samples typically come from plants found in cold and wet glaciated conditions. This is in stark contrast to pollen from modern times, which is consistent with desert plants growing in this region today.
Last ray of sunshine
In addition to pollen samples, the researchers used a third dating method, called ‘optically induced fluorescence’. It is a way of measuring the amount of ionizing radiation and shows how long ago the quartz grains from the sandstone layer were exposed to sunlight. The method determined that quartz samples from the sedimentary layer where the footprints were located went underground at least 21,500 years ago.
Since these three independent pieces of evidence all come to the same conclusion, there is a high probability that the human footprints are actually about 21,000 to 23,000 years old. This makes them the oldest human traces found in North America, and definitively sidelines alternative theories about America’s first humans.
