Discovery of 23,000-year-old footprint fossils reshape the history of early human migration into North America

Many are familiar with New Mexico as the infamous home of a fictional blue meth manufacturer from TV, but it also holds a significant place in the hearts of archaeologists due to its White Sands National Park. This park, with its extensive history, has come to become a piece of the complex puzzle of human evolution.

Back in 2009, archaeologists made an astounding discovery within the park's layers – 61 footprints of varying sizes. These footprints narrated tales of ancient human traditions and life in a region that was significantly different during the last ice ages, far from the arid terrain we see today.

What's remarkable is that these ancient humans found their home in the region, thriving during a time when one might not expect them to. Human history is woven with tales of migrations driven by climate, food, and environmental factors. Unravelling when these migrations occurred is an ongoing endeavour.

Until recently, experts believed that early humans arrived in North America around 13,500 to 16,000 years ago. However, these 61 footprints tell a different story, dating back approximately 23,000 years. This revelation has posed a challenging mystery, leaving archaeologists with a 7,000 year gap to fill.

This new estimate was established by dating Ruppia cirrhosa seeds found within the footprint fossils through radiocarbon dating. This process measures the deterioration of specific carbon isotopes within the material to determine its age. Yet, this new dating method faced scrutiny last year.

Sceptics questioned whether R. cirrhosa, an aquatic plant, might have absorbed carbon from the surrounding water, potentially dating back thousands of years before the plant itself existed.

To solidify their findings, the research team pursued additional dating methods. They isolated tens of thousands of conifer pollen grains from the same soil layer as the pollen. This confirmed that the plant and the cirrhosa seeds coexisted. And because this was a terrestrial plant, its carbon had to come from the surrounding air.

Radiocarbon dating, the same method that dated the seeds, also confirmed the age of the pollen. Furthermore, the pollen samples originated from plants associated with colder glacial conditions, a stark contrast to the present desert vegetation's pollen found in the region, as explained by David Wahl, a co-author of the study.

The researchers utilised optically stimulated luminescence, a different dating method, to determine the age of quartz grains based on their last exposure to sunlight. This method confirmed that quartz samples from the layers with footprints were at least 21,500 years old, supporting the other two conclusions.

With three robust lines of evidence, the research team has effectively demonstrated that humans arrived in the region around 7,000 years earlier than previously estimated. This discovery adds another intriguing chapter to the story of humanity's past. Now, the next step is to delve deeper into the lives of these ancient ancestors.

The findings of this research have been published in Science and can be accessed here.