Nova (1974–…): Season 39, Episode 5 - Ice Age Death Trap - full transcript

100,000 years ago
on planet Earth,

huge sheets of ice
surge and retreat

This just doesn't happen, man

Well, it's happening

In your lifetime

Now, a stunning find
in an ancient lake

promises a glimpse into
this exotic Ice Age realm,

and at the fantastic creatures
that ruled the land:

ancient elephants like mammoths
and mastodons,

giant bison, sloths and camels

Tusks, skulls, pelvises,
shoulder blades



It was phenomenal

There were so many bones

But there is a mystery
about this find

We really don't have a way
to explain this

They're finding thousands of
bones of many different types,

but most of them are mastodon,
ancient elephants

In the depths of the Ice Age,

entire families
of these mighty beasts

came down to this ancient lake
to browse

And their bones reveal
tantalizing clues

that very suddenly, something
may have wiped them out

It all starts
to make you think that,

"Boy, there was something about
this lake that was dangerous"

What were these animals
doing here,



and what is it about this lake
that killed them?

This is definitely
a mammoth graveyard

For these bone detectives,

it's a dream site that comes
with a twist

A dam is planned here,

giving them just 50 days
to dig out the fossil clues

That skull is massive

Can they solve the riddle
in time?

"Ice Age Death Trap,"

right now on this NOVA/
National Geographic Special

Major funding for NOVA
is provided by the following:

Supporting NOVA

and promoting public
understanding of science

And the Corporation
for Public Broadcasting, and:

Additional funding from:

Inspiring tomorrow's engineers
and technologists

100,000 years ago,
here in the Colorado Rockies,

massive ancient elephants
called mastodons

gather on the shore
of a small lake,

a watering hole

But a catastrophe may be
stirring beneath their feet

Today: Snowmass, Colorado

30 feet down in the muddy bottom
of that same ancient lake,

paleontologists are digging up

a stunning number
of mastodon bones

It may be the biggest
mastodon find ever

A lot of baby bits

A baby tooth, got another
baby tooth over here

They are also unearthing
the remains

from other Ice Age creatures

This is insane

This is insane

Like this horn of a giant
extinct bison

But it's the mastodons
that confound them

We think this may be one of the
largest mastodons ever found

So we got that rib,
this tailbone, that rib

It looks like an entire group
of mastodons died here

So there's the tusk

Tusk still in the skull

This busted right through
the skull

Did something catastrophic
happen

to kill off all these
ancient elephants?

And what was it?

The mystery starts to unfold
in October of 2010

Bulldozer driver Jesse Steele
is digging out a new reservoir

for the Snowmass ski resort

He notices something coming off
the blade of his dozer

That's when I discovered

that I had jawbones
and teeth of something,

and I had no clue
what in the world it was

I laid my hand
on top of the tooth

and I could still see
the tooth around my hand

The jawbone was probably
about that big

It turns out the tooth
and the jawbone

are from another type of ancient
elephant: a mammoth

And then we got
another tusk over here;

we presume it's probably
mastodon

The Denver Museum
of Nature and Science

is called to the scene

Oh, my God,
that leg bone is big!

Overnight, a construction site
becomes a fossil dig

I've never found a mammoth
before and I can tell you,

it's thrilling to, like,
be digging with the shovel

and then suddenly there's
a giant, four-foot long femur

And that is just a startling
experience

As they continue to dig, one
mammoth quickly becomes two

This is absolutely phenomenal,
just phenomenal,

to find an entire rib
this long, this thin,

in absolute perfect condition

It's like the day
the animal died

Then more of the extinct bison
emerges

That's unexpected

This is a bison

That's nice

A portion of its jaw and teeth

Anybody got a toothbrush?

Gonna brush the bison's teeth

Remember, up and down motion

Then they unearth
the vertebra of a mastodon

Doesn't have a crack in it,
so it's not leaking very bad

It's not just large,
it's in perfect condition

Amazing

And the variety of bones here

shows this watering hole
was a busy place

We found a pelvis of an unknown
animal, we found a deer jaw,

we found a bunch
of mastodon parts,

and then this morning we found
a sloth tooth

It's totally incredible

What's now a natural basin
was once an ancient lake

In digging for the dam,

heavy equipment had cut deep
into its ancient bed,

revealing its history

This slice through the earth

went down 30 feet
and back 150,000 years,

revealing fossils
from top to bottom

The basin first formed
150,000 years ago,

when it was gouged out
by a glacier

As the climate warmed,
the glaciers retreated,

leaving a watering hole
surrounded by lush forest

Over 70,000 years,
the climate cooled again,

and the lake became a tundra bog

Today, when the dam is finished,
it will once again be a lake

At each layer in the lake,
they find hints of the animals

that visited this ancient
watering hole

It is a unique repository

of nearly 100,000 years
of Ice Age history,

ending at its top layer,

45,000 years ago

The museum team works feverishly
for two weeks

until the snow shuts them down

They find the remains of four
mammoths, ten mastodons,

an extinct bison
with a six-foot horn span,

an American camel,

and a Jefferson's ground sloth,

and they have barely
scratched the surface

Wow, just check that out

It is a treasure trove

One tooth of an Ice Age mastodon

And a mystery:

How did all these animals die?

The dig will resume in the
spring, but time is limited

Construction on the dam
must move ahead

Time is the one thing
we don't have

We have everything else
besides time

Could this massive cache
of bones at Snowmass

shed light on the vanished world
of the Ice Age?

The question of what causes
ice ages is hotly debated

The leading theory
connects it to a wobble

in the way the Earth spins

That wobble changes the angle
of sun hitting the Earth,

shifting it nearer to
and farther from the poles

Less direct sunlight on the
poles means ice sheets grow,

setting off a chain reaction

For North America, that meant
that massive glaciers

repeatedly ground their way
southward,

reaching as far as present-day
New York, and then retreated

When North America was cooler
and the glaciers advanced,

the ancient lake site
at Snowmass was cooler, too

There was grass there,
but fewer trees

When the continent warmed
and glaciers retreated,

Snowmass also warmed

Forests around the lake
grew lush,

drawing families of mastodon

Furry and chunkier
than its mammoth cousins,

the mastodon was built to fight

Averaging five tons,

it was about the size
of today's African elephant,

but more robustly built

The giant Bison latifrons
also flourished in the warmth

At two tons, this one was twice
as big as today's bison,

with up to eight-foot headgear

One top predator of these
warm-weather animals

was Smilodon,
the saber-toothed cat

About six feet long
and 600 pounds,

Smilodon used its bulk
to subdue prey, not its teeth

Only when the prey was down
would it sink its enormous fangs

into a victim's windpipe
and jugular

When the world cooled
and the glaciers advanced,

another set of creatures
came on the scene

Columbian mammoths were the
largest of the Ice Age icons

and probably lived
in matriarchal families

At 13 feet tall
with 12-foot tusks,

they were larger than
today's elephants

But these giant plant eaters

faced plenty of plus-sized
predators

Short-faced bear,

one of the largest bears ever
to walk the Earth,

might have targeted
mammoth infants or weak adults

It stood an imposing
11 feet high when upright

Another animal that actually
evolved in North America

was Camelops

Analysis of the backbone
of Camelops

suggests it was a one-hump camel

Both mammoths and camels

were also likely hunted
by dire wolves,

some of the largest and fiercest
wild canines that ever lived

What became of all these
Ice Age mega-beasts?

Snowmass, with its collection
of pristine fossils,

presents an unprecedented
opportunity

to understand this lost mountain
world of ice and animals

And not just animals

Oh, my God

There is a green leaf

It's even changing color
as we watch it

The diggers found still-green
plant fossils

that hadn't seen the light
of day in 100,000 years

Fossil sites are pretty common

But what is not that common
is to find a place

where you have multiple
fossil sites

stacked on top of each other,

and even less common is to find
multiple fossil sites

stacked on top of each other

that have amazing preservation
of different kinds of fossils

It's almost like a movie

where we are seeing different
frames of the movie

as time progresses,
as the climate changes,

as animals come and go,
as plants come and go

We're getting these little
snippets of this landscape

changing through time

During the snowy winter,

the museum team carefully
piece together their finds,

including the enormous skull
of a Bison latifrons.

Project leaders Kirk Johnson
and Ian Miller

lay plans for the final
spring dig

36 scientists from 17
institutions and four countries

have signed on

May 15

Let's do it

Day 1 of 50

What's the safest way to get
over by the bison?

As we move around,

be really careful about the
slippery mud and the deep snow

Kirk and Ian lead the first team

into what will have to be
a scientific sprint

Just follow the deep footsteps

Use your shovels
as a walking stick and

And a probe

Yeah

For normal fossil digs, we don't
usually have a time limit

No one fires a gun and says,

"Okay, you have 50 days
to solve the problem"

It's really hard to sort of
wrap your mind around

how much dirt is there, how many
fossils are in that dirt,

and getting that work
actually done in 50 days

Failure is not an option

Ian has calculated
that every digger

has to move two cubic yards
of mud and dirt per day

for the excavation
to finish on time

That's the equivalent
of digging a small grave

It's deeper than it looks

During the fall dig,
they figured out that this lake,

formed by a glacier
over thousands of years,

filled up in three layers

The bottom, made up of rocks
and dirt,

where they found
warm-weather creatures

like a sloth and a puzzling
number of mastodon bones

The middle, made up of silt,
where they discovered

that massive skull from
the ancient Bison latifrons.

And the top, made up of peat
and clay,

where the first cold-weather
mammoth was found,

along with hints
of several others

But having exposed the bottom
layer, 30 feet down,

they uncover something curious

Sloping in from the side,

evidence of ancient landslides
full of boulders

Surprisingly, they're
finding mastodon bones

mixed into the landslides

Kirk and Ian call these
landslides debris flows,

and have a little contest

to show how bone-rich
they really are

This is an ancient debris flow

that came off the edge
of the lake

And it's so full of bones,

we think we could find
a bone in five minutes

This is a five-minute challenge

Three, two, one, go!

We got five minutes;
we gotta find a bone

These debris flows have a bone
about every two or three feet

Totally unexplored

Okay, this piece
is gonna come out

Here is a beautiful
150,000-year-old stick,

the wood is pristine!

Another stick

Bone!

Bone?

Yup!

Bone!

Holy

What is that?

It looks like a

It's a scapula

Yeah, scapula What's the time?

Three minutes

Well done

We are honorable people

The bone turns out
to be the forearm

of a Jefferson's ground sloth

The few sloth bones found here
are the first remains

of this strange animal
found in Colorado

More ground sloth bones emerge

We've just uncovered the skull
of a Jefferson's ground sloth

Sloths survive today
in tropical forests,

and most are about the size
of a dog

But these ancient sloths
were the size of a grizzly

Well, the ground sloth is a very
strange-looking animal

It kind of shuffled around
on the sides of its feet,

had a very large tank-like
fermentation, tank-like body,

and a very deep, strange snout

But by far the strangest part of
a ground sloth were its arms

It has these really muscular
large arms,

which were tipped
with giant claws,

which were used to grab and
grapple with trees and hook them

and bring them down
to its mouth for feeding

These were these were
lawnmowers of trees

This is fab

This is my favorite fossil
so far

A few weeks into the dig,

they're pulling out
hundreds of bones a day

Most of them are mastodon

So we're looking at the lower
jaw of a mastodon...

This is the back of the jaw
and the front of the jaw,

both come together...

And you can see
these two amazing little tusks

that stick out the front
of the jaw

As the excavation
in the spring unrolled,

it became pretty clear to us
that this was a mastodon story

The overwhelming drumbeat was
mastodon, mastodon every day,

lots and lots of mastodon bones,
mastodon tusks, skulls,

pelvises, shoulder blades

It was phenomenal,
there were so many bones

That is an amazing fossil
right there

So, what were mastodons
really like?

Dan Fisher is the world's expert

on the two ancient elephants
found here,

the mastodon and the mammoth

Though related,
they are quite different

Mammoths tend to be rather tall,
rather slender

We could say elegant animals,

long in the limb,
relatively short in the torso

Many of them have rather long
and strikingly curved tusks

Mastodons in contrast are
a little longer in the torso,

a little shorter in their limbs,

bulkier, more bulldog-like,
somewhat more massive tusks

Like modern elephants, mastodons
probably moved in matriarchal,

close-knit families of mothers,
aunts and children,

with males traveling alone

The mastodon's bulldog build

reflect the male's
violent lifestyle

Their bones bear the marks of
epic battles, like these ribs

Smashed during a fight, they
fused together while healing

This mastodon,

now mounted in the University
of Michigan's museum,

was killed by a fierce uppercut
to the cheek

Even modern elephants
occasionally fight to the death,

but mastodons were brutal

We have good evidence
that mastodons,

particularly mastodon males,
were rather ill-tempered

We have excellent evidence,

in the case of a number
of specimens,

that they ended in death
for various mastodon males

There's evidence of really
dramatic fights, uh,

slamming tusks
into the opponent,

in some cases,
goring an opponent

But mastodon-on-mastodon
violence

could not have killed
this varied group

There are animals of all ages
and both sexes here

So what happened
to the mastodons?

Was there a mass die-off?

That's gorgeous

Almost perfect

Why are the bones concentrated

in those debris flows
full of boulders

that look like landslides?

As we dug, and as we started
to realize that

the bones were very concentrated
in these layers

that looked like
they were debris flows,

slumps coming off
the side of the lake,

we said, "Wait a minute,
maybe there is something here,

"maybe there is something
that is actually

killing these animals
and then burying them"

It's not just a place they go,

but it's a place they go
and accidents happen

So the question is,

What kind of accidents might
happen to kill these animals?

40 days into a 50-day dig,

nearly 90% of the bones emerging
are mastodon

Most are found in the oldest,
bottom layer

But a few mastodon bones
are found mixed in with logs,

much higher up,
along the ancient shoreline

Paleobotanist Ian Miller
explains that the site

opens a window onto the world
of the mastodon

So here's a log, and we've
cut it out of the way,

and this is a mastodon pelvis

It was sitting
underneath the log

You can see one half
of it right here

and the other half over there

And what is amazing is

this suggests or this shows
definitively that

this tree was living here
when this mastodon died

So we are getting a picture
of this lush forest,

the animal in the lush forest,
it dies,

its hips end up here
on the shoreline

The tree dies,
rolls down the banks of the lake

and then lines up
on the shoreline

The trees suggest it was warmer
100,000 years ago

than it is today

The mastodon's watering hole
would have been ringed

by fir and spruce much more lush
than today's Aspen,

making Snowmass
an elephant resort

100,000 years before it became
a human one

But was it a resort
where bad things happened?

Among the debris fields left
by the landslides,

those deposits of dirt,
rock and boulders,

the scientists find teeth that
indicate mastodons of every age

lived here and died here

There are a lot of animals
that did not make it

through their whole lifespan
in Snowmass

Something caused them
to die prematurely

It wasn't just a nice lake
to go drink

and occasionally drop dead
and get buried;

it was a lake where if you were
there at the wrong time,

something might kill you

What we in fact have at Snowmass

is something
that looks more like

a snapshot
of a living population

It really looks like what you
would get

if you took a whole family unit

and just flipped the switch
on them all at the same time

What could flip the switch
on a family of mastodons?

The landslides look like
they could have been caused

by an earthquake

But how could an earthquake kill

an entire population
of mastodons?

Particularly deadly is

an earthquake phenomenon
called liquefaction

When earthquakes hit an area
where the water table is high,

it mixes solid ground with water
and creates a kind of quicksand

into which even entire buildings
can sink

Dan Fisher wonders if
liquefaction could explain

how all these mastodons died

And the scenario that I began
to entertain,

and all of this you realize
is just, "Hmm, what if,"

was that animals
could have been, say,

down to drink for the day,
to drink, to bathe,

to play in the water of the
lake, the ancient lake

Everything was fine, they walked
in and the substrate was firm,

as it always had been
in their experience

But if an earthquake then struck

and we began to get
that trembling

and if then the sediment
began to be

to undergo this process
of liquefaction,

it would then change
to pudding, essentially

And animals that had been
standing comfortably

on a substrate could begin
to sink down into it

Maybe only to their ankles,
maybe only to their knees

But when the shaking would stop,
within a matter of seconds,

that sediment would change back
again to its firm state

And if they were in
up to their knees,

there would be no way they could
work themselves out

And Kirk has a theory
for how their bones

got from the shoreline
where the mastodons died

to the bottom layer of the lake

Then maybe the same process

that made the quicksand
in the first place,

that shake that liquefies,

maybe another earthquake
happened,

and you get a second event

where you slide or slump the
sediment into the lake bottom,

this debris gets created,

and that would give you
those dispersed bones

So we started calling that

the shake-kill-shake-bury
hypothesis

But there are scientists
who doubt that liquefaction

could have occurred at Snowmass

One is USGS geologist
Eugene Schweig,

who joins Kirk for an experiment

So what we're going
to do here is

try to duplicate the conditions
that might have existed

at the times the mastodons

were roaming around
the site at Snowmass village

So you're going to make me
a lakeshore here

I'm going to make you something

that's probably like
the lakeshore was

So the lakeshore of course is
made up of a mixture of sand,

and all I'm using here
is playground sand

to imitate what we have, and I'm
mixing this sand with water

And you can see right now that

there's water
on the ground surface

I think we've got plenty
of water in here

What we're going to do is

we're going to mix
the sand and the water

And as I stir this up,

you can see that
the water's disappearing

between the sand grains

It was at the surface, now the
sand's looking drier and drier

It's quite amazing how fast
it goes to dry

You can see the water disappear

between the grains,
sort of, yeah

So you've got
drier-looking sand now

I'm going to smooth it out,

make it look a little more
like a real beach

So the question is,
how solid is this stuff now?

Well, let's take
this wooden elephant,

which is going to be our
stand-in for a mastodon,

and put him on the surface
and see,

and it feels to me like
it's pretty solid,

you can put your weight on it

Really solid, you can't
really push it in at all

That's right, it looks
fairly solid right now

In fact, I'm pressing down
with pretty good weight

on the elephant

If this were real life,

he would feel like he was
walking on a solid surface

And so he's sitting there,

he's walked out to feed
on the sand by the shore

Well, let's say
an earthquake comes along...

And to simulate an earthquake,

you and I are going
to shake this table

Shake the table

And see what happens
to our mastodon

Ready?

The water's coming out

The water's coming out

And the elephant's going down!

The elephant's going down

As the shaking's going on,

the water pressure's
building in the sand

and turning it more
or less into quicksand

and under his own weight,
the mastodon is sinking

He's up to his knees now

That's right

That was pretty good

That was good

Oh, wow

I'm so excited

He is stuck in there

Just wedged in

That's right

And so the real question is,

couldn't he just get out
at that point?

Well, I don't think so

If I feel the surface of the
sand now, if feels pretty solid

It's already starting
to solidify

And with time in a real system,

this water would probably drain
into the lake off the surface

and this sand would become
as solid as it was before

It would be very, very difficult
for him to get out

But he's already stuck
side-to-side in this thing

When I first heard about
this idea of earthquakes,

I was pretty skeptical

Having done an experiment
like this,

and seeing how something

that probably would have
less trouble staying upright

than a real mastodon,

I'm pretty impressed that he can
sink vertically like this

Analysis of seismic records
by the U S Geological Survey

suggests that earthquakes
powerful enough

to cause landslides
and liquefaction

would occur in this area about
seven times every 100,000 years

And we have 100,000 years,
more or less, to work with,

so it's not beyond belief

Is there any hard evidence
for this provocative scenario?

It could be hidden
in the tusks of the mastodons

It was from Dan Fisher's work

that we collectively learned

that the tusks of mammoths and
mastodons are not just tusks

They're ivory tape recorders
of that animal's life

Tusks are teeth

And all teeth grow
by addition of layers

to an existing structure

So there's actually time markers
within the tooth itself

or the tusk itself

So there's a record
of the animal's environment,

the animal's diet,

even aspects
of the animal's behavior

and reproductive biology,

that's all encoded
within the structure

and composition
of tusks and teeth

There's also a record
of their deaths

Mastodons put down
layers of new material

in their tusks every two weeks,

kind of like the rings on a tree

The thickness of the layers
varies with the season...

Thicker when food is abundant,
thinner when it's scarce

Comparing the pattern
of thickness in the last layers

with the pattern
in previous layers

reveals the season in which
an animal died

Dan will analyze the small tusks

that jut from the chins
of mastodons,

called mandibular tusks

First, every specimen
is molded and cast

And before he cuts
into the fossils,

they are scanned in 3-D
and photographed

to ensure an accurate record
of shape and condition

After cutting a specimen,

they examine thin sections of
tusks that are highly magnified

They compare the tusks
from two different animals

both found in the same landslide

at the bottom
of the ancient lake

The arrows indicate faint
but distinctive lines on tusks

that mark the transition
from winter to spring,

a record of when sparse forage
gave way to abundant new growth

But in both cases,

the layers just after the last
winter-spring boundary

look highly unusual

To Dan, they seem
unexpectedly thin

Not what you'd expect
for an animal

feeding on the abundant food
of springtime

My guess is that

some of these last
couple increments

are not life as normal

for that animal in Snowmass
100,000 years ago,

but those could have been the
weeks or the month or something

that they spent trapped,
after the seismic event,

sort of up to their knees
in consolidated sediment

That could be why these
are as thin as they are

But that's really remarkable

how similar those
two ends of life are

Never would have expected that

When they analyze a third tusk,
they find the same result

Spring brought the death
of another mastodon

There we had three individuals

from the same
stratigraphic horizon

with indistinguishable seasons
of death

Now, that was
I can't say surprising,

but it was still, uh,
sort of a shock that,

"Ah, maybe there is
something to this!"

Two streams of evidence,

one from the tusks, one from
the bones in the debris flows,

come together to suggest
a chilling end

to many of the mastodons at
Snowmass over 100,000 years ago

Family groups, comprised mainly
of mothers, aunts and calves,

might have been grazing along
the shore of the ancient lake

when the ground beneath
their feet began to shake

and rapidly turned to quicksand

They were trapped

But mysteriously, there are
no gnaw marks on their bones

Where were the scavengers?

For now, it's unknown

Still, given the intelligence
and close bonds

among living elephants,

it must have been
a harrowing end,

because ahead lay weeks
of starvation

It is terrible to think about,

and I guess I want to make
the point that

you only get to that point

by really identifying
with the animals,

thinking in detail about
what were the circumstances

of their lives and their deaths

And if you just treat them
as remains, bones,

you know, this one, that one,

you sort of never get to
the point where you really ask

some of the questions that need
to be asked to figure out

some of the things about
what events represent

the cause of the assemblage
that we have at Snowmass

But the dramatic demise
of the mastodons

isn't the only mystery
at Snowmass,

a site that spans 100,000 years

20 feet above
and 60,000 years later,

the lake was a tundra bog,

the setting for another
baffling case

This one involves the remains
of a large mammoth that,

to the untrained eye,
look like a jumble of bones

But mixed in with
the mammoth bones

are a small number of boulders

The puzzle is this:

the lake is filled
with boulders,

but all of them
are around the edges

and at the bottom
in those landslides

But the top layer is made
of clay and peat;

there are no boulders

Except for here

How did they get here?

So this is a clay mammoth

Any thoughts yet on what was
going on with the rocks?

Well, this is why
Bryan and I stopped

We were looking at this

You knew this wasn't consistent
with the rest of the geology

The Denver Museum team
is anxious

for Dan Fisher to have a look
at their rocky dilemma

They show him the evidence,
a mammoth embedded in clay

with a few boulders mysteriously
scattered amongst the bones

Boy, I don't know

But I sure agree this is unusual

We just don't see rocks
in the peat and the clay

I know it, I know it

We know there were landslides
here 100,000 years ago

Couldn't the same thing
have happened again,

60,000 years later?

If so, there would be
a lot more boulders

than just this isolated few
among the mammoth bones

What's clearest here is that

we do not have a good
geological explanation

for the association
of rocks and bones,

nor do we have a good
explanation that involves,

let's say, mammoth behavior

If the rocks didn't get here
by some geological means,

Dan has to consider a truly
radical alternative,

one that upends
conventional thinking

Here in these
40,000-year-old sediments,

could human hands have been
at work?

One possibility for explaining

the presence of these boulders
in amongst the bones

has to do with the idea that
perhaps we could be dealing

with a meat cache here

That is, a place
where carcass parts

were being stored by humans for
later recovery and utilization

I know that gets
into the issue of,

"Were humans here at this time?

Do we have human involvement
at this site?"

We don't know

But we sort of have to
consider all possibilities

Dan has uncovered sites
like this before,

where human hunters
used boulders

to anchor mammoth carcasses in
a lake, away from scavengers

All of those meat cache sites

date back to about
10,000 years ago

But if humans did the same thing
at Snowmass,

it would mean they were here
in North America

some 30,000 years earlier
than previously imagined

It's a very controversial idea

What's the plan to proceed here?

How should we approach this?

You have to prepare
as if it's going to be

the site of the century

Right

And then maybe it's not

The question of how and when
people got to America is

one of the most contentious
issues in archaeology

Starting in 1929,

several discoveries were made
of distinctive,

exquisite stone spear heads,
named Clovis points

after the New Mexico town
where they were first found

The people who made them

were long considered the first
inhabitants of the Americas,

crossing a land bridge from Asia
some 13,000 years ago

Many believe they hunted

the great beasts of the Ice Age
to extinction

Their Clovis points have been
found among the remains

of mastodons and mammoths

For decades, the idea
that the Clovis people

were the first Americans
was gospel

But recently, a growing number
of finds,

like these well-documented tools
found in Texas

dating back 15,000 years,

suggests that other people
may have been here earlier

But to push the arrival
of the first Americans

back an additional 25,000 years
is a truly provocative idea

So excavating a mammoth
in 45,000-year-old sediments

with even the slightest hint
of human involvement

will have to be done carefully

So how goes clay mammoth?

In just half an hour of digging,

they've found three more
mysterious boulders

Everyone on-site is intrigued
by the possibility

that this was a human-made
meat cache

In fact, there's more rocks here
that we have uncovered

in the last, what, half hour?

So when we came
there were these three

There's now this one,
the smaller one here,

a big one there,
and Mike's got one over there

We have doubled the number
of rocks, maybe

That's one of the puzzles

Meat caching was
an ingenious strategy

since the chemistry of lake
water has a preservative effect

A mammoth this size could
provide 4,000 pounds of meat,

enough for a band of hunters
to live off of for months

A lot of times, people, I think,

just assume that when, say,
Paleo-Indians hunted a mastodon

that they set up racks
and started making jerky,

and for the next month
they were making jerky

But whose kid, whose family
is going to carry

all that jerky in their pack?

What's going to happen

when the dire wolf
or the short-faced bear

comes for some of that jerky?

Junior's get the jerky pack

And think of all the time you
put in to making it, you know

You going to lose that?

Just put the carcass in the pond

and come back to it
when you need it

God, it's amazing,

a whole technology for storing
and retrieving barbeque

But extraordinary claims
require extraordinary proof

To obtain it, they will have
to pin down a more precise date

for the age of the mammoth
and the clay it rests in

In a bid to find out,

they'll sample the clay
and cut a bone sample,

and then try to date it

There's a bit of a smell

All right

You smell it?

A little bit, a little bit

The distinctive burning smell

suggests there is viable protein
inside the bone

The fossil bones of Snowmass

haven't been mineralized
into stone yet,

and are little changed
from their original state

Excellent

Wow

Outstanding

Excellent

That's the bone we are after
right there

Yeah, it was smelling quite nice
while I was drilling

Yeah

Organic-y

Yes, blackberry, cherry

hint of oak,
hint of tobacco, yeah

Clearly been in an oak barrel
for three years

Nice, thumbs up

All right, sweet

As they search for an additional
bone to sample,

they make a more dramatic find

I'd be happy for it
to break somewhere

I think that's just clay

Unless it's another piece
of bone

No, it's something

No, I see it now,
it's a piece of bone

It's a rib fragment, one with
unusual marks on it

That's interestingly different

It's not clear what it is

Is it a rib?

It's a fragment of rib

Yeah

It's got marks

We have to get this

Oh, my goodness, look at that

The parallel marks,
like the boulders,

don't appear to Dan to have
a natural explanation

From the rock, you think?

It can't be, this is the side
that's down

The side that's down
has marks on it

Predator?

No, I don't think so

That does not look like gnawing,
that's too short for gnawing

That does not look like
gnawing damage to me

Those are linear marks

They're very sharp

Neither rock damage nor
the tooth marks of predators,

what these parallel marks
look like to Dan,

is evidence of cutting
with stone tools

Could these,
along with the boulders,

be the earliest evidence
of humans in the Americas?

Richard Stucky, Denver's head
of vertebrate paleontology,

takes a look

Well, that's interesting

I agree

So just with my naked eye,

I said I thought that looked
to me not like gnawing

Well, I'd agree with that

The lines are pretty parallel

They're parallel,
they're straight,

they are sharp bottomed

There are many of them
right there

That is an interesting pattern,
that's for sure

Hmm

Cool!

And so we really don't
have a way

to explain this,
marks on a bone,

which don't look like gnaw marks
made by a carnivore

They look more like marks made
by human tools,

lithic tools, stone tools

Cut marks that could be
associated

with the removal of meat from
this particular piece of rib

What else, we're not quite sure

There is another curious detail:

only the front half
of the mammoth is here

Paleo-Indians were known
to favor mammoth brain for food

and their tusks for tools

Still, Richard Stucky
is not convinced

I'm a devil's advocate
at this point in time

I think there are natural ways
that we can understand

the boulders associated
with the scratch marks

associated with the bones

to suggest that this could be
certainly a natural event

that could have taken place

Let's see if we find more

The idea that humans butchered
and cached this mammoth

will remain controversial
until they find more evidence

So they're covering the fossil

and all the dirt around it
in a plaster jacket

The entire death site will be
taken back to the Denver Museum

for detailed examination

With only a day to go,
they've reached their goal

Who'd believe we've pulled
almost 4,000 bones

out of this site
in the last six weeks?

This whole thing is
just solid bones!

With 50 shovelers in there,
you can dig anything

In just six weeks' time,

they have pulled more than 4,000
bones from the ancient lake

It will take years for the
scientists to study them all

And the mysteries continue

Among the mammoths
and mastodons,

where are the predators?

Do their bones lie
among the thousands

that have yet to be examined?

What could explain their strange
absence from this site?

The riddle of the clay mammoth

is an enigma wrapped
in a mystery

and now wrapped in plaster

Weighing five tons,

the entire package
is carted off whole

Does it hold the key to when
humans first came to America?

Dating of the mammoth bones
proved inconclusive

But the clay itself
was definitively dated

to 45,000 years ago,

suggesting that the mammoth
itself is that old, too

So what does that say about
human involvement?

In my mind, it's highly unlikely
that it's a human site

It's just so unlikely

that humans would have been here
for 20,000 years

and we have no evidence for them

and we happen to find it
in Snowmass village

But stranger things
have happened

I mean, it would be one of
the biggest science stories

of the decade

It would be so cool
if it were humans

But it's going to give us
amazing information either way

I'm just excited
to crack the jacket

and see what's inside there

And for Dan, who has studied
more meat caches than anyone,

those boulders among the mammoth
bones demand explanation

We have to do a lot of work

to investigate all the
alternative interpretations

of what we see
at the clay mammoth

But, right now, it's a puzzle

It's a puzzle that demands
our attention,

and I know it will get
a lot of it

Now, the plaster jacket
has been cracked open

and scientists are slowly
working through

the bone and clay

More of those strange boulders
have emerged,

but so far no more cut marks
and no stone tools

If this ancient mammoth was
an unfortunate victim

to the first human pioneers
in the Americas,

it's keeping its secrets
to itself, for now

The exploration continues
on NOVA's website,

where you can watch any part
of this program again.

And hear the story
of mortal combat

in the Nebraska Badlands.

Two male mammoths found locked
in a death grip.

Why and how did they die?

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