There are preserved footprints of life in the wide expanse of an ancient lakebed. The marks left by giant sloths and mammoths are still visible today. According to research published in September 2021, these footprints are "definitive evidence of human occupation of North America" during the last ice age. The evidence of such an early age is disputed by a new study.
According to scientists from DRI, Kansas State University, the University of Nevada, Reno, and Oregon State University, the dating evidence is insufficient for claims that would change our understanding of when and how humans first arrived in North America. The new study shows that the footprints could have been left a long time ago.
Charles Oviatt, a professor of geology at Kansas State University and one of the new study's authors, read the original Science article and was struck by how much the footprints were on their own. There could be problems with the scientific tests of the dates reported in the paper.
David Rhode is a paleoecologist at DRI and co-author of the new study. It's important to nail down this age because we need better evidence.
Historians and archaeologists use a number of different methods. Scientists agree that the earliest known dates of colonization of North America are between 14,000 and 16,000 years ago. If the original claims are correct, current chronological models need to be reexamined.
It's in a time period where you need to pay attention to how people got into North America. It's possible that people had to come here much earlier than that because the pathway down the Pacific Coast wasn't very accommodating.
Paleogeneticists theorize that the American Southwest was occupied no earlier than 20,000 years ago because of the rates of genetic change found in ancient human fossils. The use and integrity of these genetic models could be questioned if the footprints are older.
It's possible that the ages from one study at a single site in a New Mexico lake basin are valid, and that age estimates from a variety of other fields are not.
The small seeds of an aquatic plant are at the center of the debate. Researchers examined a type of carbon known as Carbon 14 in order to identify the time of the seeds' birth. Plants take carbon-14 from the atmosphere and use it to make food.
The amount of Carbon-14 in the atmosphere and the amount of plant material can be compared to determine the age of the fossils. The plant species used, Ruppia cirrhosa, grows underwater and is able to get a lot of its carbon from dissolved carbon in the water.
The basic biology of the plant is underestimated by the researchers. The majority of the time, it's using the carbon it finds in the water. Most of the time, that means it's taking in carbon from sources other than the current atmosphere.
The method is likely to give an estimate of the plant's age. Ancient carbon enters the water from the eroded bedrock of the Tularosa Valley and the surrounding mountains.
The authors used a known age from the same region to show how this effect works. The University of New Mexico herbarium has a collection of living Ruppia plants. The plants that were alive in 1947 returned a radiocarbon date suggesting they were about 7,400 years old, an offset due to the use of ancient ground water by the plant.
According to the authors, the real age of the seeds would be between 15,000 and 13,000 years old, which is in line with other archaeological sites in North America.
The authors write that there are other methods that can be used to determine the age of the footprints.
Rhode says that the trackways are a good place to understand the past. I would like to see them myself. I'm careful about the ages that the researchers put to them.
A critical assessment of claims that human footprints in the Lake Otero basin, New Mexico date to the Last Glacial Maximum, Quaternary Research is available. There is a book titled " 10.1017/qua.2022.38".
Journal information: Science
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