Children left tracks
in New Mexico around 22,500 years ago thousands of years
before most scientists thought humans settled in North America.
Ancient footprints found
at the New Mexico site. The tracks were dated to between 21,000
and 23,000 years old, and probably belonged to children and
teenagers.Credit: National Park Service, USGS and Bournemouth
White Sands National Park, in southern New Mexico, is known for
chalk-coloured dunes that stretch for hundreds of square kilometres.
But at the height of the last Ice Age, the region was wetter and
grassier. Mammoths, giant sloths and other animals walked the muddy
shores of shallow lakes that grew and shrank with the seasons. And
they had company.
In a landmark study published on 23 September in Science,
researchers suggest that human footprints from an ancient lakeshore
in the park date to between 21,000 and 23,000 years old. If the
dating is accurate which specialists say is likely
the prints represent the earliest unequivocal evidence of human
occupation anywhere in the Americas.
The evidence is very convincing and extremely exciting,
says Tom Higham, an archaeological scientist and radiocarbon-dating
expert at the University of Vienna. I am convinced that these
footprints genuinely are of the age claimed.
The dates raise questions about when and how humans from Siberia
settled in the region, with evidence growing that they skirted the
Pacific coast while inland routes were entrenched in ice. The authors
of the study say the footprints give credence to contentious evidence
of even earlier signs of settlement in the Americas.
The paper makes a very compelling case that these footprints
are not only human, but theyre older than 20,000 years,
says Spencer Lucas, a palaeontologist at the New Mexico Museum of
Natural History & Science in Albuquerque. Thats
For decades, archaeologists associated the earliest Americans with
11,00013,000-year-old stone spear points and other vestiges
of Clovis culture (named after another New Mexico site,
but found throughout North America). The dates coincide with the
recession of a continent-size glacier, which created an ice-free
corridor through central Canada.
The discovery of numerous 'pre-Clovis' archaeological sites, from
Alaska to the tip of South America, dating to as old as 16,000 years,
sowed doubts about the Clovis-first hypothesis and argued
for a coastal migration route from Siberia.
Research journals are dotted with claims of even earlier sites,
including a controversial Nature paper that put humans in California
130,000 years ago. But many of these claims have been discounted
because of the equivocality of the evidence: rocks potentially mistaken
for tools, marks on animal bones that might have been made by natural
processes or diggers, in the case of the California claim
rather than butchery.
Excavations in White
Sands National Park reveal human footprints at the base of
a trench.Credit: National Park Service, USGS and Bournemouth
White Sands is filled with human and animal fossil footprints
in 2018, the same team that found the tracks in the latest paper
documented a giant sloth hunt on a dried-up lake bed known as a
playa. But these tracks are notoriously difficult to date, says
study co-author Matthew Bennett, a geoscientist at Bournemouth University
in Poole, UK, who specializes in the study of fossil footprints.
Every time you uncover something its potentially a different
age. Dating is a nightmare.
In 2019, study co-author David Bustos, an archaeologist and resource
manager at White Sands, identified a site on the playa that had
tracks that led right into layers of rock-hard sediment. The rock
contained seeds of spiral ditchgrass (Ruppia cirrhosa), an aquatic
plant that could be carbon-dated to determine the age of the tracks.
Thats the holy grail of trying to date footprints,
He and his colleagues werent surprised when radiocarbon dating
by researchers at the US Geological Survey in Denver, Colorado,
determined that the seeds were between 21,000 and 23,000 years old,
because a previous small-scale excavation had dated the sediment
to around the same time. But Bennett says the team knew that claims
of human occupation at this age would draw extreme scrutiny.
So they attempted to address factors that could skew the seeds
ages. The most likely was a phenomenon whereby organisms incorporate
carbon that has leached into the water from nearby rocks, such as
calcium carbonate in limestone. Such carbon sources tend to be much
older than the carbon in Earths atmosphere.
The researchers say such reservoir effects are unlikely.
They dated hundreds of seeds in different sediment layers and their
ages fell into line, with older seeds at the bottom, younger on
top. If the seeds had incorporated old carbon, there would probably
have been more variation, says co-author Daniel Odess, an archaeologist
at the US National Park Service in Washington DC. At a site in the
region that didnt have any footprints, spiral ditchweed seeds
date to the same age as charcoal in the same layer which
is not subject to reservoir effects.
I really think those ages are okay, says Thomas Stafford,
an experimental geochronologist at Stafford Research Laboratories
in Lafayette, Colorado. Even a 1,000-year error wouldnt tarnish
the importance of the footprints, he points out. Whether people
were here 20,000, or 22,000, or 19,000 years ago, does not change
their incredible story, Stafford adds. We have human
The team determined that the several dozen tracks probably belonged
to numerous individuals, mostly children and teenagers. To
me this makes perfect sense, says Odess. When I was
young I was always heading to the water. Stream, river, pond, whatever
it was. Given the chance, I would probably walk in mud more than
Karen Moreno, a palaeoichnologist at Austral University of Chile
in Valdivia, has no doubt that the tracks are human. She isnt
yet convinced that they were mostly made by children, because these
estimates are based on the statures of modern people. But she says
the tracks could shine a light on the earliest humans in America.
This older community most probably had a different and complex
way of life.
Now that there is strong evidence that humans settled the Americas
more than 20,000 years ago, researchers should grapple with the
consequences, says Bennett. He hopes the White Sands footprints
will force researchers to reconsider sites that have more equivocal
evidence of early human occupation.
David Meltzer, an archaeologist at Southern Methodist University
in Dallas, Texas, is convinced by the White Sands footprints, but
disagrees that they give credence to the more controversial sites.
However, if stone tools or other artefacts associated with the track-makers
could be discovered, this could allow such connections to be drawn,
The footprints make it extremely likely that the ancestors
of the White Sands humans and other early settlers travelled along
the Pacific coast, says Higham. The next step will be to identify
the people who arrived through these Ice Age voyages, he adds. An
urgent research priority is not just to find footprints such as
these, but the remains of the people who made them.