Nova (1974–…): Season 44, Episode 28 - Day the Dinosaurs Died - full transcript

Investigate how an asteroid vanquished the dinosaurs 66 million years ago. Join scientists as they drill into the impact crater and, for the first time, reconstruct the hell on earth that unfolded in the minutes, hours and months ...

Are you wondering how healthy the food you are eating is? Check it -
66 million years ago, the
ultimate catastrophe:

a massive asteroid
slams into the Gulf of Mexico,

blasting an enormous crater.

The impact wipes out most of
the world's known species,

including the dinosaurs.

The asteroid impact is the only

global instant catastrophe
we know of.

It happened in a day.

It caused such environmental
disaster to our planet,

that 75% of all life
went extinct.

But how did a local event

trigger a worldwide cataclysm,

killing dinosaurs everywhere?

To find out, "NOVA" is following
an extraordinary expedition

to drill deep
into the asteroid crater.

It's a really big effort
on the human scale.

People are just really excited
about the science.

Science that will reveal
new evidence

about one of Earth's
most devastating catastrophes

"The Day the Dinosaurs Died."

Right now, on "NOVA."

Major funding for "NOVA"
is provided by the following:

Check it out.


Horn one, horn two, horn three.

In the Badlands of North Dakota,

a giant skull, long hidden,
is unearthed.

That's a lucky find to get
the tip of the horn there.

It belongs to a triceratops,
the most famous horned dinosaur.

This skull is
amazingly intact...

Paleontologists Tyler
Lyson and Kirk Johnson

suspect they've just uncovered
one of the largest skulls

ever found
of this plant-eating dinosaur.

So here we are excavating
a beautiful triceratops skull.

From the beak, all the way
to the back here

it's six-and-a-half
feet long.

You can see one of
the brow horns right here.

The other brow horn
is sticking out right here.

This is the piece that fell off.

And then all the way back here,
we have the big shield

from here, all the way over
to here.

Which basically means the skull

is about four-and-a-half
to five feet wide.

This thing would of been about,
probably about, you know,

four or five elephants in size.

An absolute monster
of a triceratops.

Over 700 species of dinosaurs
have been identified.

For about 170 million years,

these creatures ruled the earth.

Then suddenly, without warning,
they vanished.

To appreciate the extraordinary
scale of this extinction,

it's important to understand

just how successful
the dinosaurs were.

Dinosaurs are found in
every habitat that we know of...

From the equatorial deserts
to above the Arctic Circle.

They were the dominant group
of animals

in the terrestrial realm
all over the world.

So let's look over here.

If you're looking for clues
about the dinosaur's fate,

there is no better place
to search than North America.

In New Mexico, Steve Brusatte
and Tom Williamson

want to know how dinosaurs fared
during the Cretaceous,

an era lasting 79 million years.

That's bone, yeah?

Yeah, okay.

Got a bone layer.

Whoa, look at this.
Check this out!

So this area here
was a dinosaur paradise

during the late
Cretaceous period,

so the final ten million years
or so of the time of dinosaurs.

And so at this site right here,

we have a lot
of different bones.

It's a bone from the backbone
of a horned dinosaur.

This is probably pentaceratops,

which means
five-horned face.

Two brow horns, a nasal horn and
then a cheek horn on each side.

Pentaceratops, a plant eater,
is a cousin of triceratops.

Pentaceratops was the main
plant-eater on the landscape.

These were
the cows of the Cretaceous,

they would have been everywhere.

But there were other
plant eaters, too.

It was incredibly diverse.

Now the things that were feeding

on those plant eaters

were some of the most famous
dinosaurs of all,

the tyrannosaurs...

So we have T. rex
here in New Mexico.

During those ten million years,
this was essentially a jungle.

It was dense vegetation.

Big trees,
kind of like the Amazon today.

Maybe not quite that extreme,

but the world was so much warmer
in the Cretaceous.

So this just promoted evolution.

You had lots of species

And so that was the world that
these dinosaurs were living in.

But the long reign of the
dinosaurs was about to end.

Evidence can be found back
in the Badlands of North Dakota,

where Tyler Lyson
and Kirk Johnson

have almost finished
excavating their skull.

Triceratops were some
of the last dinosaurs

to roam the earth.

A clue to their fate
lies in a rock formation

called Hell Creek,

deposited between
68 and 66 million years ago.

The Hell Creek Rock Formation

preserves Earth's
very last dinosaurs.

So if you want to understand
what killed the dinosaurs,

you come to this particular
rock unit to figure it out.

And there is one layer

in particular
that marks the bitter end.

On a nearby butte,
Kirk looks for it.

There it is.

Right along here.

This little thin clay layer
doesn't look like much.

But it represents
the single worst day

in Earth history.

It's called the K-T boundary,

and it's been found
around the world.

So for the past two years,
my team and I

have been searching
the rock layers

right above and right below
the K-T boundary.

And we found triceratops,
duck-bill dinosaurs,

T. rex, thescelosaur,

any number of dinosaurs
right below the K-T boundary.

But we have yet to find

a single dinosaur fossil
above the K-T boundary.

What could have happened
at the boundary

to wipe out dinosaurs
around the world?

The first clue was found
in 1980,

when geologist Walter Alvarez

and his father Luis,
a physicist,

tested clay from the boundary.

The results stunned them:

the layer contained
a huge spike in iridium,

an element that's rare
in the earth's crust,

but common in space rocks.

And they realized,
this must have been

one really big meteorite,
an asteroid

that had hit all at once
and spread iridium dust

all around the planet.

Once they thought of that,
they said, "Wow, that means

that a giant asteroid happened

right when the dinosaurs
went extinct?

It was a radical idea.

But how big would an asteroid
have to be

to end the reign
of the dinosaurs?

The Alvarez team calculated
that the asteroid

was almost seven miles wide.

Traveling at over 40,000 miles
an hour,

it exploded with the energy
of billions of atomic bombs.

As molten debris, fire,
and smoke enveloped the planet,

nearly 75% of all known species
were wiped out.

It was the first
compelling theory

for how the dinosaurs died.

Given the force of the impact,

where was a crater of the
right age, type, and size?

At first, nothing seemed to fit.

While everybody was looking
for Alvarez's crater,

someone had already found it.

But no one paid attention
to him.

Geologist Glen Penfield
had been searching for oil

as he flew over
the Gulf of Mexico.

To find buried deposits,

he was measuring changes
in the earth's gravity

and magnetic fields,
looking for aberrations.

On one of these flights,

he came back and mapped
the patterns he saw.

And what he got was this amazing
giant circular anomaly,

which he interpreted
to be a giant buried crater.

But why are the rocks
in the crater so magnetic?

It's a question geologist
Sonia Tikoo has been studying.

When the impact took place,
it introduced

a lot of heat
and a lot of shock pressures

into the rocks that were there.

This one got so hot
that it completely melted.

And here's a rock that simply
broke apart from the force.

Maybe it was a little
farther away.

So, whenever these rocks
melt and they cool down again,

they form these
magnetic minerals in the rock

that can make them so magnetic,

that they can move
a compass needle.

But the rock that broke apart
doesn't move the needle at all.

So a great contributor
to the discovery of this crater

was the fact that you had

this anomalously strong
magnetic signal

from these very strongly
magnetized molten,

or formerly molten, rocks.

In 1991, scientists finally
determined that the crater

was the right age and size
for the asteroid impact.

It was named Chicxulub,
after a nearby town.

But finding the crater
only raised new questions.

How did the impact unfold?

And why did a local catastrophe

trigger a global
mass extinction,

killing dinosaurs everywhere?

To find answers,

a team of scientists
has come to ground zero.

From a huge rig
towering over the buried crater,

they'll drill
deep into the earth.

Overseeing this
multi-million-dollar operation

is geophysicist Joanna Morgan.

Everybody wants to know
what killed the dinosaurs.

And this particular event
led to our own evolution.

So it's the most important event
on Earth

in the last 100 million years.

Woohoo, here we go!

Her co-leader is Sean Gulick,
a marine geologist.

This is the ultimate test
of some ideas.

And they are not only my ideas,

they're all the ideas of people

who have been modelling
how impacts work

and how modelling
how the extinction happened,

but without some samples
from ground zero,

we can't really test them.

And so we're investigating

how this impact occurred and how
it impacted life on the planet,

and how it led
to such mass extinction.

On an earlier expedition,
the team measured

the buried crater to figure out
the best place to drill.

We're looking
for impact features.

And so we basically

take sound energy, we send it
down into the subsurface,

and it bounces off layers,

and comes back
and makes us a picture.

The asteroid had punched a hole
nearly 20 miles deep,

gouging a crater 124 miles wide.

Over 40,000 cubic miles of rock
were displaced,

rising into towering mountains.

So this is an absolutely
amazing event,

mountains like the size
of the Himalayas

were formed in seconds.

As the mountains collapsed,
they formed what's known

as a peak ring... found only in
the largest of super craters.

It's the only peak ring
left on earth.

The next nearest is on the moon.

Until now, no one has ever
drilled into a peak ring.

So scientists don't know
if it's made from rocks

that came from deep in the earth

or nearer the surface.

Finding out how far
these rocks traveled

is key to understanding just how
the violent the impact was.

We figured that this
was the spot,

we would have the best record
of what happened at ground zero,

right after the impact.

To grasp the enormity
of the Chicxulub blast,

Sean visits Meteor Crater
in Arizona.

This simple crater here
was created

by about a 150-foot asteroid
impacting the Earth

about 50,000 years ago.

It's about a mile across.

So while this looks like an
enormous crater in human terms,

it's actually
of the smallest class

because it's just a simple bowl,
and we can see

that there has been no rebound
in the center of the crater.

Although there's no peak ring,
like Chicxulub's,

the impact was still violent.

So it comes in at something
like 26,000 miles per hour.

It hits this spot,

and it actually vaporizes
and ejects most of the material

that's inside the crater itself.

The intense heat of the fireball
sent shock waves

travelling over 12 miles
from the blast.

Gale force winds
raged up to 24 miles away.

So it would have been a really
dangerous thing locally,

but certainly not a global event
50,000 years ago.

If this is what
a 150-foot asteroid can do,

imagine one
over seven miles across,

with a crater 100 times wider.

Back at the Chicxulub
drill site,

the team is working
round the clock.

To get to the buried crater,

they must first drill
through nearly 2,000 feet

of limestone sediments.

Only after crossing
the K-T boundary,

and broken, melted impact rocks,

will they reach the mountains
of the peak ring.

An underwater camera,
shows the drill,

encased in a pipe,

as it bores through
the sea floor.

After reaching a certain depth,
it's time to alter the drill

and start collecting
rock samples.

This is the drill bit.

Each one of these little nodules
is an industrial diamond.

So as this drill bit spins, it
basically cuts away a doughnut.

This kind of drilling
s actually coring,

so the teeth, if you will,
are on the sides of the bit,

and there's a hole
in the center.

So as we're drilling down,

we're literally collecting
a column of rock.

And as we go further down
the borehole,

we go further back in time,

until we actually get
to the moment of the impact,

about 66 million years ago,

and then beneath that
everything is in the crater.

The drill extracts cylinders
of rock ten feet at a time.

Okay, so this is the first
full core of the expedition

we're excited to say.

This core contains limestone
sediments laid down

for millions of years
after the impact.

But how old are they?

What we're actually looking for,

is when we are in time,

and how you're going
to figure that out

is by the organisms that lived
in the rocks at the time,

so the fossils.

To find these fossils,

pieces of rock are ground up
and analyzed.

So I'm looking at it
under a microscope here,

this is about a thousand times

And let's see what I see.

Paleo-biologist Tim Bralower

spots a species from the base of
the ancient ocean's food chain

called discoaster.

Because it appeared
at a precise point in time,

and then quickly evolved
into a new species,

Tim can estimate the rock's age.

And they are telling us
that this sample

is probably about
54 million years old.

With each core,
the scientists get closer

to the moment of impact
when the peak ring was formed.

But there's one thing
they aren't likely to find:

remnants of the asteroid itself.

And the reason is most
of the asteroid is vaporized,

and it rises up
in an expanding vapor plume,

and it gets...
all that material gets ejected

all around the globe.

After weeks of coring,

Tim Bralower searches
for fossils

to see how much progress
they've made.

Let me look at this
in the microscope.

I would say somewhere between

about 64 and a half million
years ago and 63 and half.


In just ten feet, they've
drilled back ten million years.

We've been stuck
in the same zone for a while,

going forward very slowly,
and then all of a sudden,

boom, big jump in time.

This huge chronological leap

means they will soon
reach the K-T boundary.

On deck,
everyone is on high alert.

Sure enough,
the next core has light layers

and bands of dark ash.

Oh, my god!

This is Cretaceous.

Tim spots a fossil from the time
of the dinosaurs.

This one... this one lived
right up to the boundary.

Next, they hit huge deposits
of sandy sediments.

Just an ever-increasing
pile of sand.

And the fact that
it's completely structure-less,

just like you dumped it
in place,

with the coarser stuff
on the bottom

and the finer stuff at the top,

I think the only process
on Earth

that can do that is a tsunami.

Tsunamis are giant oceans waves

created by a violent

When the energy of the impact
punched a hole in the earth,

it pushed away vast amounts
of rock and water,

and tsunami waves
rushed back to fill the void.

And the fact it's already
like 12 meters thick

probably makes it
one of the largest...

Maybe the largest...
Tsunami deposit ever discovered.

And if it keeps getting thicker
as we go,

it will be absolutely,

be the largest tsunami deposit
ever discovered.

Wow, they're so different!

After the tsunami deposits,

they find rocks melted
and shattered by the impact.

I think it's getting more
chaotic as we go down.

At last, they're at the top
of the crater.

Yeah, that has to be!

Beneath them lie the rocks
in the peak ring,

created in the first moments
of impact.

Then, out of nowhere,
a road block.

I just got woken up
because there is a problem

with the drilling.

So we're going to be down
for a few hours.

But in the meantime,
I've heard that the core

that did come up, at this moment
when we hit something different,

is pretty exciting.

As Sean examines the core,
he sees signs of the peak ring.

Look at the color of the matrix.

It goes from green to red.

It contains granite,

a rock formed miles below the
earth's surface as magma cools.

We are now fully into
impact rocks directly

because it's granite,
and so you can see

these spotted, leopard-looking
big chunks.

And some appear melted.

- That looks like melt.
- That does look like melt.

Kind of looks
like a giant cluster of melt.

It's not easy to melt granite,

but the pressure of an asteroid
impact could do it.

So, in effect, these were formed

the days the that the dinos

More granite is recovered
from the peak ring,

but it's different.

It's brittle, with crystals
that are deformed or "shocked."

And this granite
looks nothing like

any granite you've ever seen
anywhere else around the world.

So this impact has done
something incredibly dramatic

to these rocks.

But how did granite,
buried deep in the earth,

rise for miles to form
the mountains in the peak ring?

It's a question
that will be studied

in the next phase
of the project.

After eight weeks at sea,

over 300 cores
have been collected.

It's time to wrap up
the expedition

and return to the lab.

I don't think it could have gone
much better.

We have very good core recovery.

So we're pretty happy.

I'll not forget this place

Once the cores
are fully analyzed,

the team hopes to understand
exactly how the impact unfolded

and turned into
a global catastrophe.

One of the biggest mysteries
is why the Chicxulub blast

wiped out dinosaurs
around the world?

Especially in places
like Patagonia, Chile,

nearly 5,000 miles from the
impact, at a site so remote,

the only way to reach it
is on horseback.

Here, Marcelo Leppe
has found dinosaur bones

at the tip of South America.

This place is known as
the Valley of Dinosaurs,

one of the southernmost places
with dinosaurs in the earth.

It's literally a bone bed
of six kilometers long.

So it was full of life.

Most of these bones comes from

one special type of dinosaur,
a plant eater.

It's a hadrosaurs,
duck bill dinosaurs.

Hadrosaurs were one of the most
common dinosaurs

to roam the planet.

After conquering Europe,
Asia, and North America,

they headed all the way south.

When they arrived here,
this valley was a river delta.

The changing climate
and falling sea levels

created a land bridge,

letting hadrosaurs
even reach Antarctica.

The changing conditions
were not a problem

for the group of hadrosaurs.

They conquered a lot
of environments.

They moved around the world.

Not only did dinosaurs
conquer every corner the earth,

they grew to extraordinary

One of the biggest ever found
also lived in Patagonia.

This titanosaur weighed
over 70 tons

and was longer
than three city buses.

So how did the asteroid blast
seal the fate of dinosaurs

thriving far from Chicxulub?

It's a question scientists hope
to answer in Bremen, Germany,

where the columns of rock,

one after another, have been
laid out on the floor.

Unravelling the secrets
of the impact

and its aftermath
is a colossal task.

Nearly half a mile of rock
must be split, tested,

and photographed.

As the cores are studied
in chronological order,

the story of the catastrophe
becomes clearer.

This core,
from above the crater,

is what the seabed
normally looks like:

layers of similar looking rock
laid down very slowly.

These ten feet of limestone

took about ten million years
to accumulate.

But after the asteroid struck,

geology moved at hyper speed.

The next 2,000 feet of rock
were deposited in a single day

as the asteroid blasted
deep into the earth's crust,

leaving a chaotic jumble
of rock.

So what we have here
are granites,

like you would have in
your countertop in your kitchen.

Only these granites are from
the Chicxulub impact crater,

and they have really been
through the ringer.

They're distressed granites.

So what caused the granite
to rise upward for miles

to form the peak ring?

So I have an example of what
normal granite would look like.

You can see how hard it is,
and that you could slab this

and make a countertop out of it.

It's remarkably solid stuff.

But this, on the other hand,
has changed completely

by the pressure waves
moving through it...

By the shock of the impact.

It's super light
and it's actually breakable,

because it's been so distressed,
so damaged.

This shocked granite
acted like a liquid.

It flowed upward like the
darkened, melted rock above it,

to create the peak ring.

And so the asteroid hits
and it opens up a big hole,

and like everything
acting like a liquid

it then splashes up
and collapses outwards.

And the ring of mountains
is then made from rocks

taken very deep
and brought to the surface.

after millions of years,

the first violent minutes
of impact

and the peak ring's formation
is exposed.

The core above,
full of shattered rocks,

tells the story of the tsunami
that followed.

This one is so unique.

It's one that has mixed things
that would never normally

be anywhere near each other,

which is pretty amazing.

If you look at the pieces
of rocks,

you see both ones with angles,

with corners on them,

and ones that are quite rounded.

Now something that's rounded
has seen water.

As the impact shattered
the earth's crust

and pushed away the ocean,
tsunami waves rushing back in

knocked off the corners of rocks
and mixed them up.

We have a big hole made,

the ocean has been pushed away,

and the ocean's
got to come back.

And it's so hot,

that it probably turns
right back to steam.

And we have this mixture

of some rounded stuff and
lots of broken stuff together

to create this interesting-
looking rock made by an impact.

But what did all this mean
for the dinosaurs?

To find out,
the scientists must figure out

the exact size of the blast.

And for that, they'll look
at the most powerful explosions

we humans have made.

This is the Nevada Test Site,

where nearly 900 nuclear bombs
were detonated.

To understand the effects
of a nuclear blast,

the military built a village
here named Doom Town.

Yeah, I can see the direction
from which the blast came.

Mark Boslough and David Dearborn
studied these explosions.

Tests like this
are really important.

Those of us who work
on asteroid impacts

we naturally started comparing
them to nuclear explosions.

It's a similar phenomenon.

Most of the damage is done
by the fireball and heat

that is generated or the
blast wave as it goes by.

The intensity of a nuclear
explosion can be measured

by the way it deforms a common
crystal found in the earth,

creating something called
shocked quartz.

The pressure is so high
in a shockwave

from a nuclear explosion

that it actually exceeds
the strength of a crystal.

So it squeezes the crystal.

When a crystal is squeezed,
it has to fragment,

it has to distort,

and that's what
shocked quartz is.

Quartz was found at Chicxulub.

So how much did the asteroid
blast shock it?

Back in Germany, Joanna Morgan
is trying to find out.

So this is a microscope image
of a piece of shocked quartz

that we recently drilled from
the Chicxulub impact crater.

There's lots of lines here.

Essentially the more lines
we have on the screen

in different directions,
the more shocked

this rock has been.

Since it's known
how much pressure it takes

to shock quartz,
Joanna can figure out

the energy released
by the impact.

This event was equivalent to
about ten billion Hiroshimas.

Absolutely enormous.

I mean, the biggest event
in the last 100 million years,

the most, you know,
catastrophic thing

that happened to the earth.

Using clues from the cores
and computer models,

the team can now
accurately reconstruct

the Chicxulub impact.

It begins
with a massive asteroid,

seven and a half miles wide,

heading towards earth at over
40,000 miles per hour.

Upon impact, it punches a hole

nearly 20 miles deep
in the earth,

shocking and melting granite.

The rocks flow like liquid,
rising over 18 miles,

before falling to form
the mountains of the peak ring.

Heat from the fireball reaches
10,000 degrees Fahrenheit.

It creates a shock wave,

which travels faster
than the speed of sound,

generating hurricane force

Within 600 miles of the impact,
everything is decimated.

So what happened to the
dinosaurs living in New Mexico?

So standing out here,

it's really hard for me
to imagine

what it would have been like
on that day 66 million years ago

when everything changed.

So when that day started,

this whole area here would have
been teeming with dinosaurs.

And then about 1,200 miles in
this direction to the southeast,

the asteroid hit.

And very quickly the dinosaurs
would have realized

that something was wrong

because there would have been
an enormous red glowing cloud

that would have filled up
much of the sky here.

That wouldn't have
really affected

the dinosaurs very much.

They would have seen it
but it wouldn't have hurt them.

Now, their cousins down
in Texas,

about 1,000 kilometers
closer to the impact site,

they were toast,
they were incinerated,

they were vaporized.

Around the world,
most dinosaurs were still alive.

But the clock was ticking.

A deadly, unstoppable chain
reaction had been set in motion.

And there's one core
from the crater

which reveals
how the Chicxulub impact

became a world-wide disaster.

It's full of dust, melted rocks,
and debris from the impact.

So now we are at the top
of the boundary layer.

So this sort of the end, if you
will, the tsunami deposition.

And then we end up in a
sort of a dark band here,

and what we think these are

is the initial falling out
of the sky, basically,

of the larger particles.

Probably things that
came out of the vapor plume,

made a trip all the way
around the world

before raining back down
into the crater.

When the asteroid vaporized,

it produced this huge plume
of rock vapor

that expanded upward
at very high velocities

and outward over the planet.

And as it went up, it cooled
and formed tiny little spheres

about the size
of a grain of sand.

Now, when these things
re-entered the atmosphere,

they got hot again,

from the friction of the air,
just like shooting stars.

But if you were standing
on the ground and looking up,

there was an incredible number
of shooting stars,

so much so that it didn't look
like individual stars,

it looked like a sheet
of red hot lava far above you,

glowing from all directions.

And the glowing hot lava
was emitting an amount of energy

that's a few times larger
than the sun.

In New Mexico, dinosaurs may
have escaped the initial blast,

but that rain of molten debris
would prove even more deadly.

Computer models show that just
11 minutes after impact,

the skies began to darken.

It wasn't really a case
of fire and brimstone

raining down from the heavens.

It was more a case of
all of that stuff

heating up the atmosphere
and turn the atmosphere

into a giant radiator.

For several excruciating

the sky radiated searing heat.

On the ground here
it would have been as hot

as a pizza oven.

And so that would have destroyed
a lot of the dinosaurs,

but it also would have started

Temperatures soared,
and smoke filled the skies.

Soot and charcoal found
in K-T boundaries

suggest that much
of the world burned.

The fire was started everywhere

which causes what's called
a mass fire.

Mass fires can be much hotter
than a normal fire.

All the leaves on the ground
caught fire,

the leaves on the trees
caught fire,

the underbrush caught fire.

There's winds at hurricane
speeds rushing into the fire,

drawn upward
into the rising flames

and they consume everything.

And this vapor quickly
spread across the planet.

It probably only took
a few hours for it to reach

the farthest reaches
of the earth.

The disaster was now
truly global.

Even creatures in the sea
couldn't escape.

Oceans don't usually burn,
but they can turn deadly.

Clues to how the ancient ocean

can be found behind
a shopping mall in New Jersey,

in an abandoned quarry.

paleontologist Ken Lacovara,

has been working
at a fossil site

that offers a glimpse of life
in the oceans,

before the impact.

As we go down this road, we go
millions of years back in time.

When we're down at the bottom
of the quarry here,

we're right
at 66 million years ago.

Back then, when dinosaurs ruled,

the world was warmer
and sea levels much higher.

So this was all underwater
at the time.

If you look up over the tops
of those tallest trees,

about 75 feet above us,

that's about the level of the
ocean 66 million years ago.

At the bottom of the quarry,
Lacovara has found fossils

of ancient sea creatures
that thrived during the reign

of the dinosaurs.

We find the remains
of mosasaurs here.

Mosasaurs are giant marine
lizards as long as a bus.

They have paddles for limbs;

they have a six-foot jaw

and with these really
ferocious teeth,

and it would fit
into its mouth here

along with scores
of other teeth.

This thing is a sea monster.

Scientists have excavated over
25,000 fossils at this site.

On display
in a nearby warehouse,

they provide a snapshot
of how the ocean changed.

What it shows us
is how a marine ecosystem

can collapse during
a mass extinction event.

And you see the last mosasaurs
die out.

And they're replaced
by crocodiles and sea turtles.

Because the smaller predators
take over

once the big apex predator...
The mosasaur...

Dies off.

And on the sea bottom,
the food chain has collapsed,

and what you have is a dwarfing
of organisms that are starving.

Fires had devastated the land,

but what caused the ocean
ecosystem to collapse?

The answer may come from
something missing in the cores...

A mineral known to be abundant
in Yucatan rocks: gypsum.

This is gypsum.

This was part of Yucatan
at the time of impact.

If we look at the core
that we've recovered

from the Chicxulub crater,

we do not find any gypsum.

It's all gone.

It's supposed to be full of it.

But it's not.

Which means that almost
the entire sequence of gypsum

that was present

at the time of impact
went into the atmosphere.

Gypsum contains sulphur.

When these particles
reach the upper atmosphere,

they block the sun
and cool the earth.

And we see this
in volcanic eruptions.

So when there's a major
volcanic eruption

the next year frequently there's
a year without the summer

because the sulfur aerosols
are still up in the atmosphere

reflecting sunlight
back into outer space.

And when it finally rains out

it's going to create
sulfuric acid.

This devastated coastal waters,
lakes, and rivers

as they turned acidic.

But the darkness that proceeded
this rain of acid

dealt a far more lethal blow.

This material,
vaporized by the impact and

released into the atmosphere,
is the killer.

The dust, sulphur, and soot
blocked out the sun.

Photosynthesis stopped
on land and in the sea

as darkness prevailed.

It was probably less
than the light that you get

on a moonless night.

Because there's no light
reaching the ground

it would also have gotten
very cold,

and within a few days
the temperatures

would have dropped
below freezing.

To find out what happened
to plants,

Kirk Johnson searches
for ancient fossilized leaves

in the Dakota Badlands.

We find leaves both above
and below the K-T boundary,

but they're different leaves.

About 60% of the species
of Cretaceous plants

disappear at the K-T boundary.

So there was not only
a dinosaur extinction,

but there was a major
plant extinction as well.

The world turns grey.

With little to eat,
dinosaurs, mosasaurs,

and nearly 75% of known species
go extinct.

What the asteroid set in motion,

rapid global climate change

The Age of Dinosaurs
is finally over.

So how long does it take
for life to recover?

To find out, Sonia Tikoo
is studying something

that at first seems to have
little to do with life at all:

the magnetism of rocks
from the crater.

The earth is essentially
a big bar magnet.

It has a north magnetic pole
and a south magnetic pole.

And whenever rocks form,

they actually record the
direction of the magnetic field

at the location
that they formed at.

So that magnetism is preserved
in rocks as a direction.

That direction changes every
few hundred thousand years,

when the North and the South
magnetic poles

mysteriously flip.

After the asteroid blast,

as the crater's melted rocks
cooled and hardened,

they recorded
the earth's magnetic polarity

at the time of impact.

And that direction shows up
throughout the crater.

However, there are
a few exceptions where,

in some of the rocks
that have melted,

there are directions present
that are the exact opposite

of what the earth's
magnetic field was

at the time of the impact.

It was puzzling discovery.

The impact was over.

So why were these rocks

when the earth's magnetic poles

flipped some 300,000 years

There's only one thing
that can last for 300,000 years

after an impact to re-magnetize
these rocks

and that is chemical reactions.

Reactions caused
as scalding water

formed new minerals
in cracked rocks,

like the red crystals
found in this core.

So the chemical reactions
that are required

to create new magnetic minerals

have to take place
at temperatures

that are at least 200°F.

That's pretty hot.

And it means that
for 300,000 years,

much of the buried crater
was a smoldering dead zone.

Only heat-loving microbes
could survive.

But above the crater,

sediments accumulating
on the sea floor

tell a different story.

Fossils collected
by the expedition

show that tiny plankton returned

within 30,000 years
of the impact.

And one of the first species
that we observed

was brados fera.

And this species is really cool

because while everyone else
is cleared out

and can't live in these
horrible, post-impact,

stressful environments,
brados fera is, like,

it's the end of the world as
we know it and I feel just fine.

Whatever survived
was now set to inherit an earth

once ruled by the dinosaurs.

But is that really the end
of the story?

Could some of the dinosaurs'
descendants still be among us?

Whenever you look
at a big extinction event,

it's not important
to look at what went extinct,

it's important to look at
what survived.

Scientists now believe

that modern birds
are living dinosaurs.

an avian group that evolved

from two-legged dinosaurs
called theropods.

Avian dinosaurs
go through the boundary.

They're the ancestors of the
diversity of living birds

that we have today,
which is at least

15,000 to 18,000 species.

So I think you can make
a pretty good argument

that we're still living
in the age of dinosaurs.

As for our mammal ancestors,
how did they avoid extinction?

On the tip of my finger
right here is a lower tooth

of something called mesodma.

It was a little guy.

It was probably about the size
of a mouse.

This is one tough little mammal
known to survive

through the global devastation.

It's a blade-like tooth.

It was able to feed on things
like insects and seeds,

so it didn't have to rely
on photosynthesis.

Mammals, which had been
small-bodied things,

rarely larger than raccoons,

suddenly found themselves
without any competition.

And those animals
rapidly evolved.

Within ten million years

of the extinction
of the dinosaurs,

there were mammals that were
as large as some dinosaurs.

Without the mammals surviving
through the extinction,

we wouldn't be here.

Because one of those groups of
survivors was our own ancestors.

They're among those
very few mammals to survive

through that extinction event.

But chance also helped us.

If the asteroid had hit just
a few seconds earlier or later,

it might have been
a very different story.

A story that might never
have included any of us.

Where it hit was particularly
disastrous for life.

Lots of this volatile material

got kicked up
into the atmosphere.

And if it had just been
a slightly different timing

relative to the rotation
of the earth,

it could have hit
the Atlantic Ocean,

or the Pacific Ocean.

And if it had hit one of those,
instead of Mexico in between,

that event might not have been

significant enough
to actually have ended

the Age of the Dinosaurs.

And, in fact, possibly,

we might not have grown
to take over the planet.

Modern humans have only been
around for about 300,000 years.

The question is can we last
even a fraction

of the multi-million-year reign
of the dinosaurs?

It's a front row seat
on the heavens.

You cannot help but be in awe
when you look at Hubble images.

Images that solve old mysteries.

The Hubble tells us
the age of the universe.

It tells us
how many stars there are.

Images that inspire us
with new ones.

Dark energy, the most important
stuff in the universe,

and we don't know
anything about it.

"Invisible Universe Revealed."

Next time, on "NOVA."

This "NOVA" program
is available on DVD.

"NOVA" is also available
for download on iTunes.