NARRATOR: For millions of years, they ruled the Earth.
The dinosaurs were the largest creatures ever
to walk the face of the planet.
[THUNDER CRACKS]
Today, only their fossilized bones remain in the badlands
of Montana and North Dakota.
This is a dinosaurs graveyard.
Everywhere bones jut from rocks and buttes.
But why, after 150 million years,
did the dinosaurs die out?
Does this line of crumbling rock mark the end
of the age of the dinosaurs?
Do these barren hills hold a snapshot of the moment
when a species died forever?
And is the doom of the dinosaurs linked to a literally
earth-shattering discovery made by an oil prospector
off the coast of Mexico?
Mysteries from the files of Arthur C Clarke,
author of "2001" and inventor of the communications satellite.
Now in retreat in Sri Lanka, he ponders the riddles
of this and other worlds.
[THEME MUSIC]
I'd like you to meet some extraordinary survivors.
A few years ago, turtles like these faced extinction.
Their eggs were the favorite food of local people,
and only a few were allowed to hatch.
Today, they're protected in sanctuaries like this,
and hundreds of thousands of them
have been able to grow to safety before being released
back into the Indian Ocean.
And they are survivors in another sense.
Turtles almost like these flourished along
with the dinosaurs in prehistoric times.
As you can see, the turtles are still with us,
but the dinosaurs died out 65 million years ago.
No one knows why.
It's the biggest whodunnit of all time,
and rival teams of scientists have been trying
to find the murder weapon.
NARRATOR: In this remote country, the badlands
of Montana and North Dakota, the Hell Creek rocks
are the pages of an open for dinosaur
hunters and paleontologists like Kirk Johnson.
Within these rocks lie clues to the Earth's history,
and Johnson believes, to the extinction of dinosaurs.
It's here among the fossils that he hopes to find the answer,
in the bones of the dinosaurs, and in the now
petrified leaves that they ate.
Now, that's a spectacular example of one of the two
[INAUDIBLE] liriodendrites bradacci,
which is the most common species at this locality.
Let's see what we have here.
See the bones sticking right out the top here?
A vertebrae of one of the dinosaurs.
You see it's cracking up already.
We leave it here, it's just gonna weather out.
So we'll pull it out and take it back to the museum/
I'm gonna just lift it right off.
There it is.
Oh, that's beautiful.
Look at that.
So we'll get a jacket on here in a second,
but we've got the backbone of a hadrosaur, it looks like,
That's incredible.
And these are the beasts that did not survive
the end of the Cretaceous.
NARRATOR: Johnson believes that, amazingly,
the date of the dinosaurs' death is written on the landscape.
Fossil hunters had noticed that, at a certain level
on the hillside, the fossils ran out.
When they looked closer, they found a strange, narrow line.
They realized this marked the division between the age
of the living dinosaurs, the Cretaceous, and the first era
after their death, the Tertiary.
Even closer analysis revealed that this line containing
iridium, a substance normally never found
on the surface of the Earth.
Right here is the boundary between the Cretaceous Period
and the Tertiary Period.
That is to say that the rocks that were deposited
as sediments above this layer were deposited
after 65 million years ago.
The rocks that are deposited as sediment before this layer
was deposited before 65 million years ago.
So if I wanna find dinosaur fossils,
I go down the hill from where I am now into lower layers,
into the older rocks.
If I wanna look at fossils that were formed from animals that
were alive after the extinction of the dinosaurs,
I go up the hill.
So it's a matter of walking up the hill and down the hill,
up through time and back through time.
The iridium layer was first discovered in 1979 or 80
by Walter and Louie Alvarez in Italy.
And they did further study, and found the layer again in New
Zealand, and also in Denmark.
Since that time, the iridium layer
has been found in more than 150 sites around the world.
NARRATOR: The scientists were baffled
to find so much iridium in such a thin line all over the world.
Some believe they knew where it came from.
It had to have been brought from outer space.
The source must've been a gigantic meteorite
colliding with the Earth.
In the scenario of the asteroid impact,
we suspect something like this.
Within hours, the rebound of the asteroid impact
has spread a cloud of dust up into the upper atmosphere,
blocking the sunlight from striking the Earth.
Over a period of months, the plants will cease
getting sunlight, and will die.
And the that animals rely on the plants,
such as the large herbivorous dinosaurs,
will have no reliable food source.
So the large animals die.
The animals that are supported by these herbivorous dinosaurs,
like large, carnivorous tyrannosaur rex,
similarly will succumb to a lack of food,
or either to direct environmental effects
of the asteroid impact.
The fact that we see huge levels of extinction of plants
at this level, as represented by the disappearance of plant
pollen and the disappearance of many species of plant
leaves, and the fact that dinosaur bones are only found
below the level suggests to me very strongly
that the asteroid impact and its resulting fallout ash layer
were the direct cause for the extinction of the dinosaurs.
NARRATOR: The Meteorite Theory was first advanced in 1980,
but unknown to the scientists, the evidence
to support it had been found years before.
A geologist was prospecting for oil and gas
off the Yucatan Peninsula of Mexico.
Using a magnetometer slung under a helicopter,
Dr. Glen Penfield was carrying out surveys
of the Earth's magnetic field.
We were for small excursions or anomalies, areas in the Earth's
magnetic field that are out of the ordinary, that are not
from the simple, predicted model of the overall Earth
magnetic field.
So we take those measurements, and we take in every one
second, say, and record it on tape and on paper,
and then we could make a profile of those.
We could make a map of them, and we could see what the Earth's
magnetic field looked like, and by interpretation,
what is underneath the surface.
This is the Yucatan Peninsula of Mexico.
And it was in this area that I first noticed
these extraordinary anomalies.
We were flying east-west lines about 400 kilometers long,
first in the offshore, and then on the onshore portion
of the platform.
I started to see, when we were 100 kilometers or so off
the coast, a pattern of very small, irregular,
high frequency excursions in the field,
which looked just like noise.
They looked just like the sort of thing
that we reject data for, a possible solar disturbance
or something.
Suddenly, I began to see anomalies that
were much shorter, very quick reversals
in the Earth's magnetic field.
The form of a half a bullseye begin to emerge.
NARRATOR: Penfield compared his findings
with another map, which measured the density of the rocks
below the surface of the Yucatan.
It confirmed that the half bullseye was
the rim of a gigantic crater, so deep beneath the Earth
it had lain undiscovered for millions of years.
When I put the two maps together
there was just one of those aha moments.
I suddenly saw this, and saw a feature 230 kilometers across
with a high degree of symmetry, and unlike anything I'd
ever seen in my either academic training
or my professional work.
And I suddenly knew.
I looked at that, and I knew that this was the signature
of a meteor crater.
NARRATOR: Now, scientists like Luis Marin from the National
University of Mexico are trying to discover
just how big the crater was.
At Chicxulub in the Yucatan Peninsula,
Marin is using deep drilling rigs
to bring rock cores from below the Earth's
surface, where he thinks evidence of the crater may lie.
The question of the size is very important in terms
of the energy released.
If the crater is on the order of 300 kilometers,
we probably can tie this into the extinction
of the dinosaurs.
The energy released at the moment of impact
is greater than the nuclear arsenal we have worldwide.
It would be as if a billion nuclear bombs
like the one in Hiroshima were exploded instantaneously.
We'd have a huge fireball that would have come out,
and then slowly things would have cooled down.
NARRATOR: Marrin bases this estimate
on the explosive energy needed to make a crater so vast.
And his core sample showed that when the meteorite struck,
it crashed through the sea into limestone.
The geology of Yucatan is unique.
There was no worse place that could have
been hit by this meteorite.
And it's perhaps the worst environmental catastrophe
the planet has experienced.
Some of the possible effects due to the vaporization
of this rock include acid rain.
It includes sending enormous dust
clouds into the atmosphere.
We're looking for the impact debris,
in other words, the material that resulted after the impact.
This is a sample that we have.
And this is what's left of the meteorite.
It was in a sample such as this that we found the evidence that
convinced the scientific community that Chicxulub
was an impact structure.
What we have here is after the meteorite or comet hit
the Earth, it produced molten rock due to the speed
at which it hit the Earth.
And then very quickly-- remember, we're
in water-- it turned into rock.
This produces glasses and impact rock,
which is what we see here.
The other pieces we see here are pieces of the basement, pieces
of the material way below that, were ripped
apart due to the collision.
And this is what we want.
NARRATOR: Once Marrin finds out how deeply the rocks blasted
by the meteorite lie, he can reconstruct
the exact shape of the crater.
And his discoveries so far have convinced
him that the Chicxulub impact could
have wiped out the dinosaurs.
We have, on the one hand, a one in a billion chance of having
an impact hitting the Earth.
And at the same time, we have just whole species being wiped
out, including the dinosaurs.
In my mind, there's no question that Chicxulub was the cause
of the demise of the dinosaurs.
NARRATOR: But some paleontologists
don't agree that dinosaurs were wiped out suddenly.
They claim that they died out over a long period.
This man, Peter Sheehan of the Public Museum in Milwaukee
is putting that theory to the test.
He organized a team of excavators
to comb the outcrops in the badlands.
The dinosaur bones they found there would either confirm
the theory of a gradual extinction,
or would point to a sudden death.
What we were trying to do is set up
an ecological study modeled after modern environments.
And when modern environments are under stress,
we find that the communities change slowly,
and the relative proportions of animals in those communities,
some animals become more common, other animals
become less common when there's a stressed environment.
So if the animals in the Hell Creek formation
were dying out gradually, we would
expect to find changes in the relative proportions of
dinosaurs in those communities.
NARRATOR: At Hell Creek, Sheehan's team dug at three
different levels in the rock.
This covered a time span of two million years.
If the dinosaurs had been dying of gradually,
the bones would have shown changes.
There are about eight families of different kinds
of dinosaurs that have been found in the Hell Creek.
The most common family is the group
of ceratopsians, including triceratops and torosaur.
These are animals with large shields and frills
on the back of their head.
They were herbivores, plant eaters.
They had a large horn on the front of their skull.
These were the most common dinosaurs in the lower, middle,
and upper.
They were always the most common.
More than half of the all fossils we found
belong to the ceratopsians.
And the next most common group were the hadrosaurs.
Hadrosaurs are duck billed dinosaurs.
They're also plant eaters.
The most abundant meat eater was tyrannosaurus, the largest meat
eater of all time.
This is the vertebra of a tyrannosaurid.
A smaller meat eater were the dromaeosaurs.
Dromaeosaurs are clawed animals, still carnivores,
but they have nice claws related to their meat eating abilities.
And they were always a lesser animal in importance.
NARRATOR: When his fossil hunters had finished,
Sheehan found no signs of a community under stress.
Throughout those two million years,
the dinosaur population was stable.
There was no evidence that doom had been approaching
over a long period of time.
It seems to have been a very abrupt extinction,
and it totally wiped out the largest life form
on the surface of the Earth, and gave rise to a completely
new set of communities.
I find the giant meteorite theory convincing,
but then I'm biased, because it was
first proposed in 1980 by my good friend Louie Alvarez.
He was a Nobel Prize winner, and one of the great scientists
of his generation.
Louie and his geologist son Walter
called this meteorite impact the greatest catastrophe
in the history of the Earth, until of course, the next one,
because sooner or later, something
similar will happen again.
But some scientists have other theories about the extinction
of the dinosaurs.
They blame disease, volcanic eruptions, drastic climate
change, the wholesale destruction of vegetation,
and even constipation.
All these theories are plausible,
and are fiercely defended.
NARRATOR: The world of the dinosaurs
was anything but friendly.
Paleontologists are trying to reconstruct
the creatures' environment to see if the picture will
yield any clues.
What emerges is a far cry from the safe world of theme parks.
The dinosaurs' planet shuddered with volcanic activity,
and baked beneath relentless sunshine.
Its inhabitants struggled to reproduce
in large enough numbers to guarantee survival.
All dinosaurs were hatched from eggs,
and it's in the fossilized eggshells
that science now searches for clues.
In the field, Professor Heinrich Erben seeks out the places
where the dinosaurs nested.
There, he finds the fossilized shells which
form the basis of his research.
Professor Erben has been studying
the thickness of the shells.
He believes they became so thin that not enough dinosaurs could
hatch out.
[SPEAKING GERMAN]
What caused the thinning of the egg
shells is of course a crucial question.
We know that the same happens today also in the living birds
and in the eggs of living reptiles
under certain conditions.
We know that the thinning of the egg shells
is due to a deficiency of a certain enzyme
called carboanhydrase.
This is due usually to stress.
In the case of the dinosaurs, it appears
that very probably change in the vegetation is responsible.
NARRATOR: Erben believes that the thinning came
with an altered climate, and that changes
in plant life at the time of the extinction bear him out.
From his collection of shell fragments,
he's even deduced how the embryos perished.
They simply dried out in the heat of the day.
If the egg shell is too thin, then there is the danger
that there is an excessive evaporation
of the inner liquid content of the egg,
and then the embryo simply dries completely,
and of course perishes.
NARRATOR: Erben's colleague, Abdul Ashraf,
also looks for clues in dinosaur egg shells.
But he analyzes their chemical composition.
His team grinds them down to powder,
and puts them through spectrophotometer analysis.
This reveals the chemicals present in the air at the time
the egg was formed.
Any poisonous elements or toxic compounds will show up here.
This process, this analysis we have found many rare elements,
like vanadium, like iridium, and also other poisons like leads.
We can see these things in the x-rays.
NARRATOR: The rare elements revealed by Ashraf's analysis
include poisonous compounds normally only found
in volcanoes and meteorites.
The toxins come maybe from volcanoes
or from asteroids in this time.
NARRATOR: His verdict?
Death by poisoning.
The egg shells contain a lethal cocktail of vanadium, iridium,
and lead, strong enough to kill off the species over a period.
Whatever wiped out the dinosaurs did not
affect their nearest relations.
Crocodiles and alligators were also around at the time,
and scientists want to discover why they survived
when the dinosaurs died.
For Professor Mark Ferguson at Manchester University
in England, alligator eggs incubated
at different temperatures provided a breakthrough.
I incubate eggs at 30 degrees centigrade,
for example, a bunch of eggs like this,
they all turn out to be females.
But exactly the same eggs, even from the same clutch
incubated at 33 degrees centigrade give you 100% males.
So 30 degrees centigrade, all females, 33, all males.
NARRATOR: For Ferguson's research team,
that discovery was just the beginning.
They also found that the temperature at which the eggs
were incubated affected more than just
the sex of the creature inside.
If it's a cool year, then the animals are smaller.
They don't eat as much food.
They're well adapted.
If it's nice, warm weather, they grow larger.
There's a plentiful food supply.
So they can adapt their metabolic rate and their body
size to a changing environment very quickly
in the same generation, in fact.
NARRATOR: Ferguson concluded that, unlike crocodiles,
dinosaurs could not adapt quickly to change.
Because of their more advanced genetic makeup,
they had to rely on slow evolution.
Now, you can't change your growth
by going in a sauna for six months, and come out longer,
but an alligator can.
So what happens is that dinosaurs, because they had
these chromosomal-based mechanisms,
couldn't adapt quickly to the changing environment.
It gets cooler.
What happens in alligators and crocodiles?
They scale done their metabolic rate.
They scale done their maximum body size.
They can adapt in a few generations.
Dinosaurs, much more highly evolved, much more like us.
They have to mutate the genes, have natural selection.
Takes thousands and millions of years.
So they adapted too slowly, and they went extinct.
NARRATOR: Another survivor, the tortoise,
provided researchers with a theory.
Doctor LR Croft had been working on human eyes
to understand cataract blindness.
He analyzed proteins from the eyes of different creatures.
It was then that clues to a 65 million year mystery
stared him in the face.
We isolated the proteins from both reptiles and from mammals.
And after purifying them, and putting them into test tubes,
we exposed them both to heat, and we
exposed them to sunlight.
And in fact, we used the roof of the University of Salford
and we left it on the roof for two weeks.
NARRATOR: Two weeks exposure to the sun
brought about a dramatic change, and suggested
a whole new scenario for the dinosaurs' extinction.
Well, we've had two weeks of sunshine here in Salford,
and you can see now that the protein from the reptile lenses
has gone cloudy.
The protein from the mammalian lens is clear.
Now, this would indicate that reptiles in sunlight
are susceptible to cataract.
Now, if there was an increase in solar radiation,
the dinosaurs, having this protein, like the reptiles,
would have become extinct because of cataract blindness.
You can see here that he can retract into his shell
and get protection from the sunlight.
Now, if you looked at those reptiles that survive
the great extinction, the lizards, the snakes,
the tortoises, and the turtles, they
can all escape them sunlight.
Dinosaurs, of course being large, couldn't.
And having this unstable protein,
they would have been much more likely to have had cataract.
So the theory is that the dinosaurs became blind due
to cataract at an earlier and earlier stage
as the temperatures increased.
NARRATOR: Croft says blindness would've meant disaster,
unable to escape easily from predators
or to find food and a mate, the whole species
would eventually die out.
The dinosaurs would have been doomed.
The solution to this fascinating detective story
may turn out to be quite complicated.
It may indeed be a combination of several theories.
In any event, the dinosaurs didn't die out completely.
The smart ones became birds.
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