Judy: When humans first
populated North America, and how
they arrived, has long been a
matter of spirited debate.
As Stephanie sy reports, a
recent study dig -- detailing
what archaeologists believe is
the oldest known footprints in
the United States is sparking
new questions and upending
long-held assumptions.
Stephanie: Within the sprawling
expanse of gypsum sand dunes in
dry -- and dry lake fads in
white sands national,
researchers have spent years
examining ancient footprints.
>> You can see this.
Stephanie: David Bustos says --
is them parts resource program
manager.
.
He and a team of scientists
discovered ancient animal tracks
here over a decade ago.
Ancient camels and mammoths,
previously buried under layer of
sand and clay, the sequence of
footprints called a track what
were revealed after a flood.
Matthew Bennett is a footprint
expert.
>> It is probably the most
important track in the Americas,
both in terms of scale,
geographical scale, but also in
the frequency of tracks.
That is what is really special
about it.
Stephanie: In 2017, the team
confirmed they had found human
footprints.
>> We are brushing out a set of
sloth prints.
Matthew found the human print
right beside the sloth print.
That is what sealed the deal.
Yes, you definitely have that
megafauna and humans together.
That is where the human side of
the story began.
Stephanie: The footprints show
how humans coexisted with large,
wild animals.
Many are of children and reveal
a story about everyday life and
play.
>> The stories of children in a
puddle created by a sloth track,
that is one of the most
fantastic things.
Children love jumping in puddles
everywhere.
Stephanie: One big unanswered
question remained, how old the
human footprints were, and
whether they showed if humans
inhabited North America earlier
than previously thought.
>> The peopling of the Americas
is one of the most controversial
archaeological debates, from an
indigenous perspective of having
always been here, from a more
traditional archaeological
perspective saying peopling the
Americas was quite a recent
event.
In the controversy, one of the
issues is a lack of good data
points.
Stephanie: That is where Jeff
peck gotti, an expert in
radiocarbon dating, and Kathleen
springer, a geologist and
paleontologist, came in.
>> We need to be able to find an
area where the footprints are in
the lawyers of sediment, where
we can find something of date
the low and above so we can
constrain the age of those track
ways.
>> You need to carve out a big
trench to what aisleways say
reveal the belly of the beast.
And get inside.
>> It is like a cross-section.
>> Exactly.
Then, the hope is ok, we found
tracks in cross-section.
Than the hope is, there better
be something that is suitable
for radiocarbon dating.
Stephanie: It turns out there
was.
Layer's of seeds from aquatic
grasses that grew near the track
way.
>> Some places, there is seeds
underneath these human
footprints.
So we know those seeds were, and
those plants were actually
actively living and dying there.
Stephanie: They used radiocarbon
dating to determine the age of
the seats.
>> If we measure the amount of
radiocarbon in a seed, and we
know how fast it decays, we can
calculate how old the plant
actually is.
Stephanie: Once they crunch the
numbers, what they found was
astounding.
>> At the very bottom where
people were starting to walk
around, and where we have the
lowest seed layer age, it is
about 23,000 years old.
At the top, where people were
still walking around and we have
the highest seed layer, is about
21,000 years old.
We basically documented 2000
years of human occupation in
this area at white sands and
long, long time ago.
Stephanie: Archaeologists have
long believed humans arrived in
North America 13,500 to 16,000
years ago, after a time of
warming had melted massive
glaciers opening up a land
passage from Asia to north
America.
>> This is so much older.
And our first reaction is, we
better check everything because
these better be right.
Stephanie: Jeff says he has a
95% confidence level in the
accuracy of the dating.
>> We are as sure as you can
possibly be scientifically, that
that is actually the case.
>> Put the evidence is not
rocksolid, save some
archaeologists.
>> The critical issues here are,
is the dating reliable?
Stephanie: David Meltzer is an
archaeologist at southern
methodist university.
He believes dating seeds from an
aquatic plant to tell the age of
the footprints is problematic,
and says it is too early to be
confident.
>> The people that are doing the
work, they are pros.
They.
Know what they are doing they
know what they are about.
Nature has a mischievous streak.
Nature has fooled us before.
The motto here is "Trust, but
verify."
Stephanie: Jeff peck gotti and
Kathleen springer with the U.S.
Geological survey expected
scrutiny, and are working to
carbon date pollen found in the
rock layer's.
Even then, there is so much yet
to uncover.
>> We want to expand the story
to not just occupation for 2000
years between 23 and 21, but
what if it looks more like this?
People were here for much
longer.
Stephanie: If the findings hold
up, it could spark a
re-examination of similar dry
lake bed sites in the southwest,
and that could reveal even older
evidence of humanity's foothold
in North America.
For the pbs newshour, I am
Stephanie sy.