Scientists have identified the earliest known human footprints in North America, left by people who lived in New Mexico some 23,000 years ago over a period of at least two millennia. Well-preserved and numbering in the dozens, the tracks are about 10,000 years older than the previous record-holder for earliest known footprints on the continent.
The groundbreaking discovery provides “definitive evidence of human occupation of North America” during the Last Glacial Maximum (LGM), when ice sheets extended as far south as New York City, while also shedding light on the “coexistence” of these communities with extinct animals such as giant ground sloths and mammoths, according to a paper published on Thursday in Science.
Though these tracks have been known about for years, a team of scientists have now constrained their exceptional age by radiocarbon-dating two layers of preserved aquatic seeds deposited above and below them.
“If you'd asked most people in the archaeological community a few years ago what the earliest site in the Americas would look like, we would have said we’d need hearths that could be dated; a few human teeth would be great so we could do genetics work; and some other human bones would be fabulous, and definitely some older-looking stone tools,” said Sally Reynolds, a mammalian paleontology at Bournemouth University who co-authored the study, in a call.
“Yet here we have the story of the earliest human presence in North America being told without stones, bones, or hearths, but by footprints and two seed layers,” she continued. “It shows you that in science, one has to be very open to the wealth of evidence that you sometimes get when you do archeological excavations.”
The White Sands footprints are known as “ghost tracks” because they are only visible in certain light and moisture conditions. Reynolds and her colleagues have been studying the fossils for the past five years, and have already published research indicating that humans in this area stalked and harassed sloths, offering a rare look at the behavior of both species during this period.
However, the new study is the first to definitively confirm the unprecedented age of these footprints, a finding that has widespread implications for reconstructing the mysterious origins of humans on the North American continent.
The advance of ice during the LGM blocked migration routes from Asia into North America, prompting many scientists to doubt that our species could have arrived on the continent earlier than about 16,500 years ago, when these barriers receded. However, tantalizing potential traces of humans before that timeframe have turned up here and there, suggesting that a small population may have migrated to the continent before the LGM.
Reynolds and her colleagues, including lead author Matthew Bennett also of Bournemouth University, have now presented the most robust evidence that humans were able to slip through to the continent before the glacial portcullis was drawn up.
“Our work has shown that the ice sheets were probably controlling entry into North America, but that we had made it in one glacial cycle earlier,” Reynolds said. “Working back from that, we think that at around 30,000 years ago, humans would have traveled from Siberia over the Bering land bridge.”
“This migration route only existed when there was some ice to lower the sea levels, but not enough ice to close the two ice sheets, so that constrains some of our timing,” she added. “It is a very exciting step change in how we understand the stages of this most important migration into North America.”
In addition to stretching back the empirical timeline of humans on the continent, the footprints contain insights about the people who lived in White Sands so many millennia ago. A lot of the tracks were made by children, which is a bias that exists in other human footprint sites around the world. Like kids today, these youngsters were probably running around, stomping, and playing more than adults, thereby leaving more footprints behind. Likewise, many of the tracks also belong to teenagers who might have been carrying out tasks on behalf of older members of their community, or just idling around together.
The presence of mammoth and sloth tracks alongside the human footprints also implies that humans during this period were hunting enormous prey. While overhunting by humans has been implicated in the later extinctions of these large animals, the White Sands tracks suggest that this earlier population managed their prey sustainably over a period of about 2,000 years, probably because it was so much smaller than later migrations.
Now that the researchers have snagged such compelling proof that humans inhabited North America prior to the LGM, they are eager to search for more traces of these trailblazers in places like Alaska, a major gateway to the continent, as well as in White Sands, where these ghost tracks have just opened a new window into our shared human past.
“It's just mind blowing the level of information we could actually get from this site, and I'm really excited at what the future will bring,” concluded Reynolds. “That's why we're also pleased that we might be able to tell the world about this and then move on, because we're so excited to focus on the future work.”