NOVA

White Sands National Park, New Mexico...

A vast, open desert that holds clues to a lost past.

At White Sands,

all good stories sort of begin with a Bigfoot.

Footprints dating all the way back to the last Ice Age.

All these circular things are fossil footprints.

That's amazing.

Mammoths over 13 feet tall.

Dire wolves, camels,

and enormous ground sloths

that roamed North America thousands of years ago.

White Sands has so many hidden treasures.

There's all these trackways here,

it's just such an incredible discovery.

Alongside them,

something even more astounding.

That is a human footprint.

Yeah, so there's

a human footprint right there.

Wow.

Ancient human journeys

printed on the landscape.

When you make tracks in sand,

they just blow away.

When you make tracks in a place like this,

where the chemistry is just right,

the tracks can last forever.

Now a team of experts is investigating

how these remarkable tracks could shed new light

on life in the Ice Age.

There's a double trail.

Somebody going this way, and somebody going that way.

Wow, that is really incredible.

: How long ago were they made?

That's amazing.

Yeah.

The Ice Age megafauna went extinct

about 11,500 years ago.

So they're at least that old.

How much older than that

is really anyone's guess at this point.

Could they provide new information about

early peoples of the Americas?

It really does put our feet prints

firmly into the past here in North America.

Here's our proof.

Footprints, footprints of our ancestors.

Can the secrets of these ancient footprints

help answer the questions

when and how did humans first arrive in North America?

"Ice Age Footprints"...

Right now on "NOVA."

The dazzling dunes of

White Sands National Park.

Sand as bright as fresh snow.

But hidden within this landscape

are traces of an ancient story

dating all the way back to the last Ice Age.

When we search for evidence of life

in the ice ages in North America,

we find things like the bones of mammoths

or maybe even hearth stones or spear points

from the people that used to live here,

and very rarely we find the remains of those humans.

But the story is still so incomplete,

there's so much more information we need to find.

That's why the discovery of footprints

here at White Sands is so significant.

Could they help answer some of the greatest mysteries

of the Ice Age?

The precise location of this site

is a secret.

These dunes cover

nearly 300 square miles...

with some rising over 50 feet.

I'm driving through these snow-white dunes.

It's kind of a surreal landscape.

Once we get through the dunes,

we'll be out in the great ancient lakebed,

and it's absolutely covered with tracks.

I'm Kirk Johnson.

As a paleontologist,

I've spent most of my career

studying the remains of ancient life.

But footprints can tell

really detailed stories about the past.

30 minutes later,

we've reached our destination:

a huge dried-up lakebed.

As the wind scours this remote area,

new prints are being revealed, and old ones disappear.

It seems like such an improbable place

to even look for tracks.

: Joining me is David Bustos.

He's leading the team of scientists

investigating the footprints.

You look out and it's just bleak desert,

and who would think that there's all these trackways here?

As my eyes adjust to the brightness,

round patterns start to appear.

So there's one there... Yes.

And there and there,

and there and there, there...

Yeah.

Oh, yeah. Those are amazing.

Uh-huh.

: The mysterious shapes are over five feet apart,

and nearly two feet across.

These are the fossilized tracks of an Ice Age giant...

a Columbian mammoth.

It died more than 10,000 years ago,

but its footprints remain.

The tracks are preserved in various ways.

Sometimes the wind fills them with different textured sand,

leaving ghostly impressions,

while others dry into hard casts which are exposed

when the softer ground around them erodes away.

One of the things that really stand out at White Sands

is just thousands and thousands of footprints preserved.

In this area, we'll see trackways

that go for ten miles in one direction

and two or three miles in another direction.

You know, there might be

over 100,000 prints throughout this large area.

Do... it's okay to walk on them?

We can walk near them and around them,

as long as we don't disturb the surface below

or add more sediment in.

We need to be careful not to

step on the fragile prints...

and the team tries to only visit the trackway areas

when the ground is dry,

and hard enough to support their weight.

The surface is always changing.

We are seeing more erosion.

Every year, more and more prints are becoming visible.

And along with the many mammoth prints here,

we soon spot traces of another large creature.

They're very common,

they'll sort of look like an S shape...

Yep. You'll see them connecting to each other.

There's one here, right?

Yep. There's another one coming through...

I think as well, right there.

Twice the size of a human foot,

and with giant, curved claws,

these are the prints of a massive ground sloth,

a beast more than double the weight of a grizzly bear,

that walked this land thousands of years ago.

So that's sort of how the story of White Sands began.

People, they've seen these incredible footprints,

and they thought that it was Bigfoot.

Bigfoot with three weird claws.

Yes.

Then we discover something even more special.

That is a human footprint.

Yeah, so there's... there's a human footprint right there.

: Wow.

Yeah, so if you look...

That is amazing.

Here's the heel.

Okay. Right here.

Scattered across the landscape

are human footprints

from thousands of years ago.

Each track is the trace of an ancient person,

the shape of their bare feet locked in the sediment.

Look at this, this is amazing here.

This actually looks like a human print right in there.

Could these extraordinary human footprints

help answer two big questions:

when did people first set foot in North America?

And did their arrival contribute to

the disappearance of giant Ice Age animals?

20,000 years ago,

Earth was in the grip of an ice age.

The climate was colder,

vast ice sheets covered much of North America...

and White Sands was not a desert,

but a huge lake... Lake Otero.

The lakeshore surrounding it teemed with life.

Giant ground sloths wielding big claws

shared this wetland with mammoths

weighing up to ten tons.

Alongside them,

packs of dire wolves hunting for a kill,

and hardy North American camels.

These Ice Age giants disappeared from the fossil record

over 10,000 years ago.

So the human footprints here are probably at least that old.

But they could be much older.

What can they reveal about the deep history

of humans on this continent,

and how they met the challenges of life in the Ice Age?

To find out,

David has assembled a team of scientists

to uncover the tracks' hidden secrets.

I'm confident in it now,

that that's mammoth, and it links to your one in the,

um, that you've got in cross section there.