The oldest known human footprints in the Americas have been uncovered at an ancient lakebed in what is today White Sands National Park in New Mexico. Dating to between 23,000 and 21,000 years old, the footprints shake up many of the widely established theories about how and when humans first arrived on the continent. 

The tracks were first spotted by David Bustos from the White Sands National Park, who had come across many of these tracks while traveling across the White Sands region. Astonished by his find, he invited a team of scientists to inspect the footprints in January 2016, marking the beginning of the current excavation program. Today, a multinational team from Bournemouth University in the UK, the University of Arizona, the US Geological Survey, and the National Park Service have published the analysis of this groundbreaking discovery in the journal Science.

Eventually, the team confirmed that the ensemble of prints had been created by humans, including children and teenagers, as well as mammoths and a dog-like carnivore. Most stunningly of all, an analysis of the surrounding sediment layer revealed that the human tracks were imprinted into the ground sometime between 23,000 and 21,000 years ago.

“These are the oldest known, well-dated, footprints in the Americas,” Dr Sally Reynolds, co-author and mammalian palaeontologist from Bournemouth University, told IFLScience. 

The story of how and when people first arrived in the Americas is still hotly debated. Until recently, the most widely accepted view was that the earliest inhabitants in the Americas were a group known as the "Clovis culture” who settled in the continent around 15,000 to 13,000 years ago.

More recent discoveries have pushed this timescale back, with estimates for the arrival of these first occupants ranging from 25,000 years ago to even 33,000 years ago. However, concrete evidence is lacking. These recently discovered footprints confidently indicate that humans were stomping around the Americas 21,000 years ago, at the very least. 

Tools and bones can migrate to different sediment layers, which are used to help date them. “Footprints are very fragile within a sediment and cannot migrate down, as a tool or bone might do under certain conditions," explained Dr Reynolds. "The number of footprints and their clear shape means that they are unmistakably humans.”

This could have some huge implications for our understanding of prehistoric human migration. Most researchers believe that the first humans in the Americas arrived from Asia across the Bering land bridge, which had formed between northeastern Siberia and western Alaska. They then traveled southwards through an inland ice-free corridor in western Canada and/or via a Pacific coastal route.

However, around 23,000 years ago, this part of the world was gripped in the last Ice Age, aka the Last Glacial Maximum (LGM). It was previously assumed that this migration through America would have been too tricky to traverse during the LGM. These bold footprints clearly say otherwise. However, it remains uncertain how exactly humans managed to make this treacherous journey. 

“In the light of the findings, this means the earliest migrations would have come via Asia, over the Bering Land Bridge, and into Alaska. We previously thought that they would move south after around 16,000 [years ago] when the Ice sheets melted and a migration corridor opened, but the earlier date from White Sands shows that humans were already in the Americas," said Reynolds. "This means that humans migrated into the Americas much earlier, but still via the same route.”