Footprints evidence of early human settlement in the Americas
Humans reached the Americas at least 7,000 years earlier than previously thought, according to new findings.
The topic of when the continent was first settled from Asia has been controversial for decades.
Many researchers are sceptical of evidence for humans in the North American interior much earlier than 16,000 years ago.
Now, a team working in New Mexico has found scores of human footprints dated to between 23,000 and 21,000 years old.
The discovery could transform views about when the continent was settled. It suggests there could have been great migrations that we know nothing about. And it raises the possibility that these earlier populations could have gone extinct.
The footprints were formed in soft mud on the margins of a shallow lake which now forms part of Alkali Flat in White Sands. The research has been published in the journal Science.
A team from the US Geological Survey carried out radiocarbon dating on seeds found in sediment layers above and below where the footprints were found. This gave the researchers remarkably precise dates for the impressions themselves.
Based on their sizes, scientists think the tracks were made mainly by teenagers and younger children travelling back and forth - along with the occasional adult.
They offer a fascinating window into what life was like for these early occupants of what is now the South West US.
The scientists don't know for sure what the teenagers were doing, but it is possible they were helping the adults with a type of hunting custom seen in later Native American cultures. This was known as the buffalo jump and involved driving animals over a shallow cliff edge.