Original subtitles

ago,

the ultimate catastrophe:

(loud crash)

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.

KIRK JOHNSON: The asteroid impact is the only

global instant catastrophe we know of.

It happened in a day.

JOANNA MORGAN: It caused such environmental disaster to our planet,

that 75% of all life went extinct.

NARRATOR: 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.

SEAN GULICK: 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."

Check it out.

JOHNSON: (laughing): Whoa!

Horn one, horn two, horn three.

NARRATOR: 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.

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

This skull is amazingly intact...

NARRATOR: Paleontologists Tyler Lyson

and Kirk Johnson

suspect they've just uncovered one of the largest skulls

ever found of this plant-eating dinosaur.

♪ ♪

LYSON: 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.

♪ ♪

NARRATOR: 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.

♪ ♪

MARK NORELL: 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.

♪ ♪

STEPHEN BRUSATTE: So let's look over here.

NARRATOR: 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.

(tapping)

WILLIAMSON: 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.

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

BRUSATTE: 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.

(roaring)

BRUSATTE: 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 evolving.

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

(birds chirping, diverse animal sounds)

NARRATOR: 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.

♪ ♪

LYSON: 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.

♪ ♪

NARRATOR: And there is one layer

in particular that marks the bitter end.

(scraping)

On a nearby butte, Kirk looks for it.

♪ ♪

There it is.

(blowing air)

Right along here.

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

But it represents the single worst day

in Earth history.

♪ ♪

NARRATOR: It's called the K-T boundary,

and it's been found around the world.

♪ ♪

LYSON: 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.

♪ ♪

NARRATOR: 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.

♪ ♪

JOHNSON: 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?

♪ ♪

NARRATOR: 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.

♪ ♪

(explosion)

♪ ♪

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.

NARRATOR: 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.

♪ ♪

NARRATOR: But why are the rocks in the crater so magnetic?

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

♪ ♪

SONIA TIKOO: 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.

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

♪ ♪

TIKOO: 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.

♪ ♪

NARRATOR: 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.

(waves crashing)

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.

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.

♪ ♪

GULICK: Woohoo, here we go!

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

GULICK: 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.

♪ ♪

TIMOTHY BRALOWER: 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.

(machine whirring)

NARRATOR: On an earlier expedition, the team measured

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

GULICK: 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.

♪ ♪

NARRATOR: 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.

MORGAN: So this is an absolutely amazing event,

mountains like the size of the Himalayas

were formed in seconds.

NARRATOR: 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.

♪ ♪

GULICK: We figured that this was the spot,

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

right after the impact.

♪ ♪

NARRATOR: To grasp the enormity of the Chicxulub blast,

Sean visits Meteor Crater in Arizona.

♪ ♪

GULICK: 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.

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

the impact was still violent.

♪ ♪

GULICK: 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.

NARRATOR: 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.

♪ ♪

NARRATOR: 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.

♪ ♪

CHRIS DELAHUNTY: 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.

GULICK: 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.

♪ ♪

♪ ♪

♪ ♪

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

♪ ♪

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

we're excited to say.

♪ ♪

NARRATOR: This core contains limestone sediments laid down

for millions of years after the impact.

But how old are they?

GULICK: 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 magnification.

And let's see what I see.

NARRATOR: 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.

BRALOWER: 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.

♪ ♪

MORGAN: 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.

♪ ♪

NARRATOR: After weeks of coring,

Tim Bralower searches for fossils

to see how much progress they've made.

♪ ♪

BRALOWER: 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.

Wow!

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

CHRISTOPHER LOWERY: 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.

♪ ♪

NARRATOR: 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.

♪ ♪

BRALOWER: Oh, my god!

This is Cretaceous.

NARRATOR: Tim spots a fossil from the time of the dinosaurs.

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

NARRATOR: Next, they hit huge deposits of sandy sediments.

GULICK: 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.

♪ ♪

NARRATOR: Tsunamis are giant oceans waves

created by a violent disturbance.

(explosion)

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, unquestionably,

be the largest tsunami deposit ever discovered.

♪ ♪

Wow, they're so different!

NARRATOR: After the tsunami deposits,

they find rocks melted and shattered by the impact.

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

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

Yeah, that has to be!

♪ ♪

NARRATOR: 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.

♪ ♪

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

GULICK: Look at the color of the matrix.

It goes from green to red.

NARRATOR: 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.

NARRATOR: And some appear melted.

That looks like melt. BRALOWER: That does look like melt.

Kind of looks like a giant cluster of melt.

NARRATOR: 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 died.

♪ ♪

NARRATOR: 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.

(explosion)

NARRATOR: 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.

♪ ♪

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

We have very good core recovery.

So we're pretty happy.

(indistinct chatter)

I'll not forget this place quickly.

♪ ♪

♪ ♪

NARRATOR: 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.

♪ ♪

MARCELO LEPPE: 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.

♪ ♪

NARRATOR: 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.

♪ ♪

LEPPE: The changing conditions were not a problem

for the group of hadrosaurs.

They conquered a lot of environments.

They moved around the world.

♪ ♪

NARRATOR: Not only did dinosaurs conquer every corner the earth,

they grew to extraordinary sizes.

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?

(lights clanging on)

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.

♪ ♪

GULICK: 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.

NARRATOR: So what caused the granite to rise upward for miles

to form the peak ring?

GULICK: 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.

♪ ♪

NARRATOR: 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.

♪ ♪

Finally, 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.

GULICK: 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.

♪ ♪

NARRATOR: 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.

♪ ♪

GULICK: 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.

♪ ♪

NARRATOR: But what did all this mean for the dinosaurs?

(explosion)

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.

(explosion)

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.

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

NARRATOR: Mark Boslough and David Dearborn studied these explosions.

(explosion)

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.

♪ ♪

DAVID DEARBORN: Most of the damage is done by the fireball and heat

that is generated

or the blast wave as it goes by.

♪ ♪

(explosion)

NARRATOR: 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.

BOSLOUGH: The pressure is so high in a shockwave

from a nuclear explosion

that it actually exceeds the strength of a crystal.

(explosions)

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.

♪ ♪

NARRATOR: Quartz was found at Chicxulub.

So how much did the asteroid blast shock it?

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

♪ ♪

MORGAN: 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.

NARRATOR: 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.

(explosion)

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 winds.

♪ ♪

Within 600 miles of the impact, everything is decimated.

♪ ♪

So what happened to the dinosaurs living in New Mexico?

BRUSATTE: 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.

♪ ♪

NARRATOR: Around the world, most dinosaurs were still alive.

But the clock was ticking.

(explosion)

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.

♪ ♪

BRIAN TOON: 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.

(lava rumbling)

NARRATOR: 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.

♪ ♪

NARRATOR: For several excruciating minutes,

the sky radiated searing heat.

♪ ♪

BRUSATTE: 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 wildfires.

♪ ♪

NARRATOR: 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.

NARRATOR: 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 changed

can be found behind a shopping mall in New Jersey,

in an abandoned quarry.

Here, paleontologist Ken Lacovara,

has been working at a fossil site

that offers a glimpse of life in the oceans,

before the impact.

♪ ♪

KEN LACOVARA: 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.

(birds chirping)

NARRATOR: Back then, when dinosaurs ruled,

the world was warmer and sea levels much higher.

♪ ♪

LACOVARA: 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.

♪ ♪

NARRATOR: 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.

♪ ♪

(growls)

This thing is a sea monster.

♪ ♪

NARRATOR: 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.

♪ ♪

NARRATOR: Fires had devastated the land,

but what caused the ocean ecosystem to collapse?

(saw buzzing)

♪ ♪

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.

(thunder rumbling)

NARRATOR: 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.

♪ ♪

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

Photosynthesis stopped on land and in the sea

as darkness prevailed.

♪ ♪

TOON: 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.

(tapping)

NARRATOR: To find out what happened to plants,

Kirk Johnson searches for ancient fossilized leaves

in the Dakota Badlands.

(Kirk blows dust off rock)

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.

♪ ♪

NARRATOR: 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 ends.

♪ ♪

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.

TIKOO: 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.

NARRATOR: That direction changes every few hundred thousand years,

when the North and the South magnetic poles

mysteriously flip.

(explosion)

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.

♪ ♪

NARRATOR: It was puzzling discovery.

The impact was over.

So why were these rocks re-magnetized

when the earth's magnetic poles

flipped some 300,000 years later?

♪ ♪

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.

♪ ♪

NARRATOR: Reactions caused as scalding water

formed new minerals in cracked rocks,

like the red crystals found in this core.

♪ ♪

TIKOO: So the chemical reactions that are required

to create new magnetic minerals

have to take place at temperatures

that are at least 200°F.

(bubbling)

That's pretty hot.

NARRATOR: 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.

♪ ♪

TIKOO: 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.

♪ ♪

NARRATOR: 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?

NORELL: 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.

(birds honking)

NARRATOR: Scientists now believe

that modern birds are living dinosaurs.

(chirping)

Specifically, an avian group that evolved

from two-legged dinosaurs called theropods.

♪ ♪

NORELL: 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.

♪ ♪

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

WILLIAMSON: 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.

♪ ♪

NARRATOR: 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.

♪ ♪

GULICK: 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.

♪ ♪

NARRATOR: 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?

♪ ♪

This "NOVA" program is available on DVD.

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