Fossil footprints could push back human arrival in North America by 10.000 years

[Psittacoraptor]

While this news is not about dinosaurs, I thought it's interesting enough to share.

Quick introduction to the topic:

The outmigration of humans from Africa and the subsequent colonization of the other continents has long been a topic of interest in various sciences. There are large differences in the understanding of human colonization between different geographic regions. For example, the appearance of humans in North America is not particularly well understood. Previously, humans were thought to have appeared in North America a millennium or two before the start of the Holocene. Now, a paper claims new evidence in the form of fossilized footprints has emerged that could push back the arrival of humans by about 10.000 years. This is big news because it would mean humans could have lived in North America for almost twice as long than previously thought. This would have a large impact on several hypotheses and theories, such as the potential causes of the megafaunal extinctions after the last ice age. The decline in megafaunal populations is usually believed to have coincided with both changes in climate and the arrival of humans, leading to debates about what killed the giant sloths and mammoths of North America - climate, humans, both or other causes.

A quick summary of the findings:

The footprints were found in White Sands National Park, New Mexico, and the oldest prints date back to the time of the Last Glacial Maximum in North America, 23.000 years bp. The sites are located south of the greatest extent of the Laurentide Ice Sheet, meaning these humans were not living in the glacial landscapes people generally associate with ice ages, but in a milder environment closer to the equator.

The evidence for human occupation spans about 2 millenia, which would indicate an overlap of humans and megafauna for at least that time period (trace fossils in the area include mammoths, ground sloths and other groups). Thus, if humans were hunting megafauna, they must have done so sustainably, because the large extinction waves of mammalian megafauna did not happen until around the beginning of the Holocene (11.700a). Generally, hypotheses blame either the sudden climatic changes of the Younger Dryas and/or overhunting by humans for the loss of North America's giant mammals. Hence, these fossil footprints further complicate the debate on the causes of megafaunal extinctions.

One problem with the study is dating. The sediment horizons containing the footprints were dated using the carbon-14 method via seeds of aquatic plants contained in the sediment. The problem with dating aquatic material using C-14 is that it potentially suffers from the reservoir effect (aka hard-water effect). This describes a phenomenon where the carbon isotopes of an aquatic organism do not reflect the relation of carbon isotopes in the atmosphere, but the dissolved carbon in the water, which includes old carbon from underwater sediments or other reservoirs like ice sheets. This increases the concentration (not sure if this is the correct term in English) of C-12 and C-13 and weakens that of C-14 in the material, making the dated age older (potentially much older) than the actual age. The authors of the paper say they have calibrated for this effect, but re-dating using other methods would probably not be a bad idea.

The paper (pay-walled):

https://www.science.org/doi/10.1126/science.abg7586

Article by the university:

https://news.arizona.edu/story/earliest-evidence-human-activity-found-americas


(photo from the linked article)