Original subtitles

Male narrator: In the beginning, there was darkness,

and then, bang,

giving birth to an endless expanding existence

of time, space, and matter.

Every day, new discoveries are unlocking the mysterious,

the mind-blowing, the deadly secrets

of a place we call The Universe.

Did a comet slamming into the ocean

cause the biblical flood?

- The tsunami wave itself was at least 50 meters high.

Narrator: Did a fiery messenger from space

reverse the fate of Christianity?

- Suddenly, at 70,000 miles per hour,

this meteor comes crashing to Earth.

Narrator: Did a fireball in the sky

wipe out the first North Americans?

- Space literally has changed history time and time again.

Narrator: A maverick group of scientists is on a quest...

- Very large comet impacts

could have changed the course of human civilization.

Narrator: A quest to defy mainstream science

and prove that human history

was rocked with catastrophic moments,

when space changed history.

[dramatic music]

♪ ♪

40 days and 40 nights of torrential rains.

The Bible's great flood and the Epic of Gilgamesh

are widespread myths that depict an event

that wiped humanity off the face of the Earth.

But was it simply a myth,

or did it really happen?

And if so, how can science explain such a catastrophe?

- There's no reason that very large comet impacts

could not have occurred during the last 15,000 years.

And there could have been, even, a globally catastrophic event

that could have changed

the course of human civilization.

Narrator: Archaeologist Bruce Masse

is a member of a small group of maverick scientists

called the Holocene Impact Working Group.

It's named for the Holocene Epoch,

which began 10,000 years ago.

His group has roiled the world of astronomy

by claiming that catastrophic impacts

have occurred much more often than supposed

and have actually changed the course of human history.

Case in point: the great flood.

The biblical story of Noah's ark

is simply one version of an ancient story

that's found in dozens of myths and legends

across the globe.

- What I decided to do is to take a look

at this worldwide distribution of flood myths,

take a sample of those myths,

and the sample I selected was 175 locations

from across the world.

Narrator: Most of these flood myths

contain striking similarities,

including the common legend

that just before the flood began,

a celestial creature with impressive tails,

raced across the sky.

- Since they didn't have a science

to understand what comets were all about,

they would try to come up with a natural solution.

So therefore, a comet might be a snake.

Narrator: Comets are known to have tails.

The visible effect of two by-products:

dust reflecting sunlight

and glowing ionized gases

roaring off the back like jet contrails.

- Interestingly enough,

you can actually have what's called an anti-tail,

where, from our point of view,

it looks like the tail of the comets

are actually pointing

in two totally different directions.

So as solar radiation streams off of our sun,

it tends to make the material

that's evaporating off of the comet

appear to recede away from the Sun.

Narrator: As seen from certain spots on the Earth,

the dust tail can sometimes curve around

so that it appears to point in the opposite direction.

- So observers on Earth

would see an object in which it looked like

there was a head with a headdress

or a horn coming out of its head.

In North American mythology, South American mythology,

it's a serpent with a horn on it's head.

In Hindu, it's a fish with a giant horn on it's head.

Narrator: In most myths, the creature's arrival

was followed by a watery disaster

that almost destroyed the world.

- If you look at other aspects of this mythology,

it's talking about, then, darkness, hurricane-force winds.

It's talking about torrential rainfall.

Talking about tsunamis.

Now, if you add all of that information together...

These are the properties that you would get

from a deep water ocean impact of a comet.

- If a comet were to strike in the open ocean,

you would really get a massive amount of energy

delivered into that part of the ocean that it hit.

Narrator: The amount of water

injected into the atmosphere would be colossal.

- We're here visiting a forge in a blacksmith shop

to show what would happen when a comet comes in

at high speeds and impacts the ocean,

delivering all that kinetic energy

into the water.

Narrator: A typical forge can heat carbon steel

to approximately 2,200 degrees Fahrenheit.

But a hyper velocity comet strike

will produce shock temperatures well over 10,000 degrees,

hotter than the surface of the Sun.

- A comet coming in from outer space

would be carrying with it

an immense amount of kinetic energy

because it's moving at such an extreme velocity.

When that impacts the ocean,

that energy is capable of vaporizing

up to hundreds of square kilometers of water,

sending plumes of steam up into the outer atmosphere.

- Normally, in the upper atmosphere,

there's only about a half a percent of water vapor.

So you get this injection

of this large amount of new water vapor.

Narrator: As the massive infusion of water

into the atmosphere rains down,

a global deluge could drown the Earth

for weeks or months.

Bruce Masse believed he had found

a possible source of the worldwide flood myth...

A massive comet strike.

But he lacked the physical evidence.

Columbia University geologist Dallas Abbott

investigates potential cosmic craters.

- Bruce Masse had compiled a set of oral histories

of catastrophic events

that sounded like they were some sort of cosmic impact,

and he found that the center of them

was around the Indian Ocean.

Narrator: Using bathymetry readings,

or satellite measurements

of depth variations in the ocean floor,

Abbott was able to pinpoint a potential impact zone.

She named it Burkle crater,

in honor of a colleague at Columbia University.

Burkle is a massive depression

located nearly 1,000 miles off the coast of Madagascar...

About 18 miles in diameter,

Burkle Crater lies at a depth of approximately 13,000 feet,

making an extensive study difficult and expensive.

But a crater this big would produce

another logical fingerprint of a massive comet impact:

a mega-tsunami.

- A comet hitting the ocean would actually be more damaging

than a comet hitting solid ground.

And that's because it would send up a gigantic tsunami

that would slam into the coast all around it.

Narrator: When massive tsunamis strike shorelines,

the evidence can persist for centuries.

Abbott turned her attention to the shoreline of Madagascar.

- At the time, I couldn't get data on Madagascar.

But the minute Google Earth came out,

I went and I looked at Madagascar.

And the tsunami deposits there were phenomenal.

I immediately found these huge chevrons,

which I think are probably

the biggest chevrons on the planet.

Narrator. Chevrons are symmetrical sand dunes

found along coastlines around the world.

Some believe they form when massive waves

slam into the coast and then recede.

Their distinctive 4 shape

may even serve as a directional marker.

- The back azimuth is a 4.

So this is inland. 4 points inland.

The back azimuth of the 4,

that tells you where the source is.

Narrator: Abbott claims that source is Burkle crater,

located hundreds of miles offshore.

But others doubt that tsunamis

have anything to do with chevron formation.

- The geologists that actually go to the sites

and do fieldwork and have looked at these,

they don't associate those with tsunami.

They associate those with windblown dust.

And so I'm skeptical that these things

have anything to do with tsunami waves.

Narrator: But when Dallas Abbott traveled to Madagascar,

she found surprising evidence trapped inside the dunes.

- We found tsunami deposits over 200 meters high.

And when we got to the top of this big hill,

we found marine fossils in the sediment.

And we found it in all of the locations

where we looked.

Hurricanes bring in marine micro fossils.

But they only bring the kind

that live in the top of the water column,

whereas the kind of marine micro fossils

that live on the ocean bottom,

they don't get transported by things like hurricanes.

Well, the Madagascar fossils are dominated

by the ones that live on the bottom.

And so they absolutely can't be just windblown fossils.

Narrator: For members of the Holocene group,

the chevrons and the micro fossil evidence

are the smoking gun.

When connected to the flood myths

of ancient societies around the world,

they help paint a compelling picture.

But the flood-comet hypothesis

contradicts the firm beliefs of many astronomers.

Cosmic impact astronomers like Mark Boslough

believe that catastrophic impacts

during the last 15,000 years

simply never happened.

- Anybody who would claim that there have been

environmentally damaging impacts during the Holocene,

during the era of humans,

has a very high burden of proof

because the probability that such a thing

even once would have happened is very small.

- The response has been that extraordinary claims

require extraordinary evidence,

because nobody believes that an impact crater is confirmed

until you actually go to the crater

and you've got samples of the impact melt body.

We still, at the moment,

don't have the evidence to prove Burkle Crater.

Narrator: In the meantime,

the Holocene Impact Working Group

believes it has found evidence of a far more recent impact.

The evidence, they say,

lies buried in the ice sheets of Greenland.

And, they say it points to a comet

that helped push Europe into the barbarism

of the Dark Ages.

In the search for extraterrestrial impacts

that have changed history,

certain facts are not in dispute.

[horse whinnies]

Sometime in the year 535 AD.,

something descended like a gray veil

over planet Earth.

It created the most severe cooling period

of the last 2,000 years

and plunged humanity into an unprecedented crisis.

[people sobbing]

- During that time period,

a very, very large quantity of ash

completely enshrouds the Earth.

It cuts sunlight off from crops that are growing on the ground.

It kills off crops that are under cultivation.

It leads to famine because it interrupts

the ability to produce food for the civilizations

that were present on the planet at the time.

- We know from historical data that starting early in 536 AD,

the Sun became very dim.

And in Mesopotamia, the sun was dim for 18 months.

And they said that during that time period,

the Sun came out for about four hours a day.

Narrator. The signature of this year without the Sun

remains to the present day.

Tree ring data from Ireland and California

shows the unmistakable signs of dramatic global cooling.

- The tree ring evidence clearly illustrates

that there was a period in the sixth century

where nutrients that make a tree robust,

that make it grow quickly,

those nutrients dwindled down to a very, very low level.

And so the tree rings are extremely close together.

Narrator. The accepted theory

blames a massive volcanic eruption

and a global ash cloud.

But impact researcher Dallas Abbott

has proposed another culprit,

beginning with evidence based on chevrons,

the 4-shaped sand dunes

that some believe are evidence for a mega-tsunami.

One set of chevrons

is located in Australia's Gulf of Carpentaria.

- I looked in satellite altimetry

for something in that part of the gulf,

because the chevrons were pointing

to a very, very small area.

And immediately, I found these two round holes

in the bottom of the gulf.

Narrator: The craters measured

7 and 11 miles in diameter, respectively.

A detailed study of sediments

pointed to an extraterrestrial invader.

- This is a deep sea core sample,

like the ones we studied in the Gulf of Carpentaria.

And when we sieved the Gulf of Carpentaria samples,

we found little bits of rock,

we found little bits of glass,

and we also found some shock minerals.

And together, these are indications of an impact.

And they suggested the event was about 1,500 years ago.

And I knew about this climate event in 536 AD.

And I thought, "Well, it would be really nice

to look at an ice core to see if we can see something."

Narrator: An ice core is planet Earth's

frozen filing cabinet of climate data,

trapping centuries' worth of airborne particles and algae.

- We found samples from Greenland,

which is about as far away as you can get on the planet

from that site in the Gulf of Carpentaria.

Narrator: The ice cores yielded startling evidence,

including magnetized melted rock called spherules

that matched those retrieved in the Gulf of Carpentaria,

two types of glass that appear to have formed

in a high-energy impact,

and a misplaced diatom,

a marine micro fossil that exists only in the tropics.

- So why should you be getting diatoms

that originated in the tropics to subtropics

all the way to Greenland?

Nobody has ever found diatoms in Greenland

that came from the tropics to subtropics.

Narrator: The microscopic evidence

pointed to a celestial impact.

- What happens is, you get a huge explosion,

and then this material goes up into the air

and travels for hundreds or even thousands of kilometers.

And then it's— you know, settles out.

Narrator: For a cosmic impact or

to create a global atmospheric effect

like the one suspected in 535 AD,

it must have enough mass and velocity

to create an epic explosion.

- The difference between a high-velocity

and a low-velocity impact

is, a low velocity impact does not create an explosion.

It can make a crater,

but it's not an explosion crater.

What we're doing here is setting up

to do a simulation of a hyper velocity impact

in the formation of a crater.

And we're using ammonium nitrate mixed with fuel oil,

so when we set it off,

it's gonna explode and make a huge crater.

It's a massive explosion that creates a big plume of debris

that gets scattered for many, many miles around.

And for the biggest impacts, it's a global phenomenon.

If this crater had been actually formed by an impact,

it would be an explosion crater,

because the object coming from the sky

is going so fast with so much kinetic energy

that it penetrates below the surface

and heats up, vaporizes, and explodes.

Narrator: A high-velocity strike

in the shallow waters off Australia

could have produced an explosion

large enough to launch sediments and particulates

high into the atmosphere.

- You can imagine that that'll get kicked up really high

and that you'll have a lot of particulate matter

up in the high atmosphere,

where it can block out a lot of the sun.

Narrator: The disastrous events of 535 AD.

Seem to fit the signature of an impact

followed by a dimming of the sun.

But finding the proof

that it all started with a cosmic impact

is more difficult,

especially when one glaring question remains.

What massive space rock could produce two craters

side by side?

They are considered heretics

in the mainstream world of astronomy.

But the scientists belonging

to the Holocene Impact Working Group

are determined to prove

that space has changed human history.

One such event may have happened in the year 535 AD.,

when a sudden darkening of the sun

caused crops to fail,

leading to worldwide famine.

Scientific tree ring data proves the catastrophe happened.

But science has yet to determine what actually caused it.

In 2008, cosmic impact researcher Dallas Abbott

discovered what appeared to be two huge craters

in Australia's Gulf of Carpentaria.

She believes they were put there by a comet.

- Well, the mainstream idea is that impacts are very rare

and that most of the impacts that happen are asteroidal.

But the data that we're finding

suggest that the impactors that hit were cometary

rather than asteroids.

Narrator: Composed of rock, gases, dust, and ice,

comets are known to break apart

when they encounter the gravitational pull

of large objects like planets.

In July of 1992, the Hubble Space Telescope

recorded exactly this scenario.

As comet Shoemaker-Levy 9 hurtled past Jupiter,

the planet's immense gravitational pull

tore the comet apart.

- Comet Shoemaker-Levy 9

broke up into several dozen fragments,

the most massive of which created an explosion

equivalent to 6 million megatons of TNT.

Now, the biggest bomb ever made on Earth

is the Tsar Bomba by the Soviet Union,

which was 50 megatons.

A single impact from Shoemaker-Levy 9

was 100,000 times more powerful.

Narrator: Could a Shoemaker-Levy 9 type breakup

have created the dual craters in the gulf of Carpentaria?

The hypothesized dual impacts appear to fit the comet profile.

But it's not a fit with mainstream science.

- A comet impact itself is very rare—

Once every 100 million to billion years.

A comet cluster would be much more rare, even, than that,

so rare that you wouldn't expect it to happen

on the age of the Earth.

Narrator: The search for positive verification

of an impact in the Gulf of Carpentaria

continues to generate scientific controversy.

But no impact hypothesis is more controversial

than the question of what wiped a famed North American culture

from the pages of history.

Millennia before European colonists

claimed it as their own,

another group of immigrants dominated North America—

That is, until someone or something

wiped out the Clovis people.

- Clovis were an ancient Paleo-Indian people

that lived in North America.

Some people believe that they were the first people

to live in North America

and that they came across the Bering Land Bridge

and radiated down into the Americas

from the north, moving south.

Narrator: Archaeological evidence,

including their famed spear points,

reveals the Clovis people thrived

during the last great ice age by hunting the mega fauna,

including huge mammoths and mastodons.

- There was a moment where the population of the mega fauna

in the Americas changed.

The mega fauna suddenly began to disappear.

And as they went down,

they brought the Clovis down with them.

- Approximately 13,000 years ago,

something happened.

Something changed the environment.

It changed it rapidly and profoundly.

And all of a sudden,

the planet was thrown back into a little ice age.

A climatic event we call the Younger Dryas.

Narrator: After many thousands of years

of retreating glaciers and warming temperatures,

the Younger Dryas period reversed the warming trend

and wreaked havoc on man and beast.

But scientists argue fiercely

over the reasons for this climactic U-turn,

especially one hypothesis that places the blame

squarely on outer space.

- The Clovis hunters

were having to adapt to new conditions.

And one of those changes could have been a comet impact

over the Laurentide ice sheet.

Narrator: The Clovis comet

is perhaps the most controversial impact hypothesis

championed by the Holocene Impact Working Group.

It claims that a comet strike

into the North American ice sheet

allowed large freshwater lakes to drain into the ocean,

altering the ocean currents

and triggering the Younger Dryas cooling period.

Ken Tankersley,

a University of Cincinnati anthropologist,

uncovered cosmic impact evidence in Sheriden Cave

in northwest Ohio.

- The layer which we found here is known as the black mat.

It's a very carbon-rich layer,

which, in this case,

is the result of intense burning.

It's composed of wood charcoal and the burned remains

of approximately 70 species.

It takes an intense fire, an intense burning,

almost an explosion, if you will,

to produce this type of carbon event.

Narrator: The layer also contained meteor fragments.

But more importantly,

seemingly indisputable evidence for a larger cosmic impact.

- We have what's called impact diamonds.

Impact diamonds, or shatter diamonds,

occur when some type of explosion

or sudden impact occurs with your surface,

compressing carbon material to create these impact diamonds.

Narrator: Also called nano diamonds

because of their minuscule size,

they are recognized

as powerful evidence for cosmic impact.

But their discovery raises many more questions.

- The supposed presence of nano diamonds

in certain locations of North America

isn't compelling evidence

for the Younger Dryas impact hypothesis,

because in some cases, it's not even clear

that those are genuine nano diamonds.

They may be graphite or graphene compounds

that kind of masquerade as nano diamonds.

Narrator: The proposed Clovis comet

also appears to be missing

one physically huge piece of evidence:

an impact crater.

To date, no telltale crater has been found.

But space rocks don't have to impact the Earth

to ignite a catastrophe.

We know because one very nearly touched off

a thermonuclear war.

In the face of widespread skepticism,

a small group of impact researchers

claim that very recent cosmic catastrophes

have changed human history.

13,000 years ago in North America,

something suddenly sent the Clovis culture

into a tailspin.

Some scientists believe that a comet was to blame.

But to date, no impact crater has been identified.

But some cosmic projectiles never reach the Earth.

Yet they can still rain down destruction

in the form of an air burst.

- An air burst is when a meteoroid or a comet

explodes in the atmosphere

before reaching the Earth's surface.

So it doesn't produce a visible crater.

A truly excellent example

of what is thought to have been an air burst

is the Tunguska event over Siberia in 1908.

It leveled 2,000 square kilometers of forest.

But there's no impact crater.

- When a comet or an asteroid hits the Earth's atmosphere,

it actually creates a wake

very much like the wake in front of a boat.

And that shock wave, the shocked air,

gets to super-high temperatures, and it radiates.

It radiates light and infrared radiation.

And then that heats up the comet or asteroid

and causes it to vaporize.

Narrator: Even a smaller Tunguska-sized meteor,

around 200 or more feet in diameter,

can produce an air burst with 1,000 times more energy

than the atomic bomb dropped on Hiroshima.

Some 13,000 years before the Tunguska impact,

the Clovis comet

could have delivered a similar air burst.

But the North American landscape

would have long ago swallowed all traces.

Whether it was a ground-impacting comet,

an air burst,

or neither one,

this climatic event

and its effect on the Clovis culture

remain a hotly debated topic.

But solving the mystery is crucial,

since the same thing could happen today

with little warning.

- Now, an impact like the Tunguska event,

a 10-megaton air burst,

say at 5,000 meters over New York City,

if that were to happen today,

would lead to the deaths of almost 2 million people,

another several million people injured,

and a couple of trillion dollars of damage.

So even air bursts, small events,

are something that are very destructive.

Narrator: In fact, they are so potentially destructive

that when a very small meteor exploded in 2002,

it could have sparked a thermonuclear war.

- In June of 2002, an event occurred

that could have changed history on Earth in a major way.

A rather small meteoroid,

maybe a couple of meters in diameter

smashed into Earth's atmosphere,

creating an air burst, an explosion up there.

- And this was an enormous explosion

over the Eastern Mediterranean,

and it was observed by satellite.

This was unusual to be over, you know,

a relatively populated area.

Narrator: At the time of the air burst,

Pakistan and India, two nuclear-armed countries,

were embroiled in a hostile military standoff

over the disputed Kashmir region.

The world held its breath as the two nuclear powers

teetered on the hair-trigger brink of war.

- So had this impact occurred just a few hours earlier,

it was at about the right latitude

to have been over Pakistan or India.

This could have been mistaken by either country

as a launch against them.

And they then might have pushed the nuclear button,

launching an all-out war.

A mistake, basically, caused by an impact.

Narrator: Now known as the East Mediterranean Event,

the blast convinced the scientific community

that predicting cosmic intruders is critical

when nuclear Armageddon is at stake.

- The vast majority of objects that hit the Earth's atmosphere

are unexpected.

The big asteroids,

the ones that could create a global catastrophe,

we've discovered almost all of those.

They're catalogued. They're tracked.

And so, we don't expect one of those

to come out from nowhere and hit the Earth

because we can see them.

It's the small ones that can catch us by surprise.

Narrator: But how much notice can we expect

if one of these massive space rocks

moves onto a collision course with the Earth?

That's the question that Mary H. from Lincoln, Nebraska, wanted

to ask The Universe.

- Mary, that's an interesting question.

We'd like to know about incoming comets and asteroids

as far in advance as possible in order to deflect them.

Now, asteroids might be found

tens or even hundreds of years before they hit earth,

allowing plenty of time to do something about them.

Comets might come in with very little warning,

only a few months or a year or two at best.

We might not be able to deflect them.

Narrator: There is no dispute

that comets and other cosmic projectiles

have the potential to cause catastrophes.

But before modern astronomy began to demystify them,

the mere sighting of a comet or meteorite

had the potential to change human history.

The year is 312 AD.

The mighty Roman empire is embroiled in a bitter civil war.

Marching into battle, the emperor Constantine

is about to meet the armies of his arch-rival, Maxentius.

The political fate of the empire is at stake.

- Constantine was a Roman emperor

famous for a number of things,

not the least of which

is his conversion to Christianity.

Constantine's adoption of the Christian religion

in the fourth century is instrumental

in the sudden popularity and the spread of that religion

by suddenly converting the Roman empire

to a Christian empire.

Narrator: Many believe Constantine's fateful conversion

occurs when he sees a fiery cross above the Sun.

Interpreting this as a sign from the Christian god,

he commands his troops

to paint crosses on their shields.

Constantine's troops emerge victorious.

Soon after, the emperor signs the Edict of Milan,

setting the stage for the ultimate triumph

of Christianity over paganism.

But some believe Constantine's vision

has an astronomical explanation.

- It's believed now that what he personally observed

was a meteoric impact against the Earth.

That he's looking skyward in broad daylight,

and suddenly at 70,000 miles per hour,

this meteor comes crashing to Earth.

His vision in seeing that is—

He interprets it as being a divine signal.

Narrator: There is one powerful clue

that could help validate this cosmic event:

a crater.

And a team of geologists may have found it

in the hills of central Italy.

Have cosmic impacts

altered the course of human history?

It's a question that provokes the world of astronomy

and even the world of religion.

In the year 312 AD.,

the fate of Christianity

may have been decided by cosmic intervention.

Just before a decisive battle,

the Roman emperor Constantine experiences a vision.

- He remembers seeing something in the sky,

and he interprets this as being a sign from god,

a sign from the one true Christian god.

Narrator: Some believe this fateful vision

was a fiery meteor

on a collision course with the Earth.

- What you would see, of course,

would depend on how far away you are.

You would see an extremely bright meteor

coming through the sky,

and you'd see it even in the daytime.

It would be blinding, perhaps as bright as the Sun.

And then it would hit the ground,

and you would see a big explosion.

Narrator: According to a Swedish geology team,

Constantine's meteor might very well be real.

And there's a crater to prove it.

In 1999, the team discovered a mysterious body of water

in the highlands of central Italy.

They claim the small lake and some 20 nearby craters

are the results of meteorite fragments.

But the evidence is far from conclusive.

Some think the craters are ancient man made reservoirs.

Others suspect they only date back to World War ll.

- There's ordinance from some of the craters

that suggests that they are actually bomb craters.

- The problem is, it's in a place

where there have been a lot of people.

And it was perhaps used as a watering hole.

It's been so overprinted by human activity,

and I don't know if that one will ever be resolved.

But it certainly could be a crater.

- One of the weakest parts

of the Sirente crater impact hypothesis

is that the shocked minerals simply have not been found.

There's no clear evidence

that there was a wham-mo type impact there.

Narrator: Cosmic impact or not,

Constantine's vision is considered

one of the most pivotal events in human history.

- Had it not been for this event,

would Christianity have become the dominant religion of Europe

and then spread to the Americas?

It's hard to say.

But it's easy to say that this one event was pivotal

in forcing Constantine

to fully embrace the Christian religion.

Narrator. We live on a planet

ceaselessly shaped by the cosmos

and occasionally by invaders raining down fire.

The power of space to alter human history

remains controversial.

But the question remains: how often does it happen?

For members of the Holocene Impact Working Group,

the answer is: far more frequently

than mainstream science currently accepts.

- So impacts over the course of human civilization

in the last 10,000 to 15,000 years,

there's no question in our minds,

have played an important role

in the development of human evolution

and the evolution of human civilization.

Narrator: But others hotly disagree.

- There just aren't enough potential impactors out there

to have hit the Earth.

And the kind of rates that they're suggesting—

Kilometer-sized objects hitting the Earth

every few thousand years—

I mean, if there were enough objects

to hit the Earth at that rate,

we'd be getting near-misses.

We'd be getting objects that size

coming between the Earth and the Moon,

you know, one or two of those a year.

And we've never seen anything like that.

The rate just isn't there.

Narrator: The debate will continue to rage,

perhaps until the very end of human civilization.

But will that end be a gradual demise

or a sudden violent demonstration

of how space can change history?