According to a paper published today in the journal Science, the footprints were pressed into the mud near an ancient lake at White Sands between 21,000 and 23,000 years ago, a time when many scientists think that massive ice sheets walled off human passage into North America.
Exactly when humans populated the Americas has been fiercely debated for nearly a century, and until recently, many scientists maintained this momentous first occurred no earlier than 13,000 years ago. A growing number of discoveries suggest people were in North and South America thousands of years before. These include the Monte Verde site in Chile that’s as old as 18,500 years and the Gault site in Texas that’s up to 20,000 years old. But each find kicks up a firestorm of controversy among scientists.
“A discovery like this is very close to finding the Holy Grail,” says Ciprian Ardelean, an archaeologist with the Autonomous University of Zacatecas. Ardelean directs excavations at Mexico’s Chiquihuite Cave, where researchers believe they have evidence for human activity in the Americas as early as 30,000 years ago.
The researchers eventually found one promising site on the eastern edge of the alkali flat. They began excavating and discovered multiple layers of human footprints, as well as interspersed mammoth prints. Most importantly, the team uncovered seeds from an ancient ditch grass called Ruppia cirrhosa sprinkled within various layers. Radiocarbon dating of the seeds established the ages of the multiple layers that contained tracks at between 21,000 and 23,000 years old, long before the ice sheets retreated. While in recent years researchers have reported possible evidence for human occupation of North America at even earlier timepoints, the earliest well-accepted site of human activity in the Americas remains Monte Verde in Chile, which dates to around 15,000 BP, and many researchers remain unconvinced that humans entered the continents much earlier.