male narrator: ln 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]
[ Skipped item nr. 26 ]
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 1 5,000 years.
And there could have been, even, a globally catastrophic event
that could have changed
the course of human civilization.
narrator: Archeologist Bruce Masse
is a member of a small group of maverick scientists
called the Holocene lmpact Working Group.
lt's named for the Holocene Epoch,
which began 1 0,000 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 l decided to do is to take a look
at this worldwide distribution of flood myths,
take a sample of those myths,
and the sample l selected was 1 75 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 byproducts:
dust reflecting sunlight
and glowing ionized gases
roaring off the back like jet contrails.
- lnterestingly 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.
ln North American mythology, South American mythology,
it's a serpent with a horn on it's head.
ln Hindu, it's a fish with a giant horn on it's head.
narrator: ln most myths, the creature's arrival
was followed by a watery disaster
that almost destroyed the world.
- lf you look at other aspects of this mythology,
it's talking about, then, darkness, hurricane-force winds.
lt'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.
- lf 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 hypervelocity comet strike
will produce shock temperatures well over 1 0,000 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 lndian 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 1 8 miles in diameter,
Burkle Crater lies at a depth of approximately 1 3,000 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, l couldn't get data on Madagascar.
But the minute Google Earth came out,
l went and l looked at Madagascar.
And the tsunami deposits there were phenomenal.
l immediately found these huge chevrons,
which l 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 V shape
may even serve as a directional marker.
- The back azimuth is a V.
So this is inland. V points inland.
The back azimuth of the V,
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 l'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 microfossils.
But they only bring the kind
that live in the top of the water column,
whereas the kind of marine microfossils
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 microfossil 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 1 5,000 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: ln the meantime,
the Holocene lmpact 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.
ln the search for extraterrestrial impacts
that have changed history,
certain facts are not in dispute.
[horse whinnies]
Sometime in the year 535 A.D.,
something descended like a gray veil
over planet Earth.
lt 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.
lt cuts sunlight off from crops that are growing on the ground.
lt kills off crops that are under cultivation.
lt 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 A.D.,
the Sun became very dim.
And in Mesopotamia, the sun was dim for 1 8 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 lreland 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 V-shaped sand dunes
that some believe are evidence for a mega-tsunami.
One set of chevrons
is located in Australia's Gulf of Carpentaria.
- l 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, l found these two round holes
in the bottom of the gulf.
narrator: The craters measured
7 and 1 1 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 l knew about this climate event in 536 A.D.
And l 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 microfossil 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 impactor
to create a global atmospheric effect
like the one suspected in 535 A.D.,
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.
lt 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 hypervelocity 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.
lt'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.
lf 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 A.D.
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 lmpact Working Group
are determined to prove
that space has changed human history.
One such event may have happened in the year 535 A.D.,
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.
ln 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.
ln July of 1 992, 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 1 00,000 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 1 00 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-lndian 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 megafauna,
including huge mammoths and mastodons.
- There was a moment where the population of the megafauna
in the Americas changed.
The megafauna suddenly began to disappear.
And as they went down,
they brought the Clovis down with them.
- Approximately 1 3,000 years ago,
something happened.
Something changed the environment.
lt 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 lmpact Working Group.
lt 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.
lt's a very carbon-rich layer,
which, in this case,
is the result of intense burning.
lt's composed of wood charcoal and the burned remains
of approximately 70 species.
lt 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.
lmpact 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 nanodiamonds
because of their miniscule size,
they are recognized
as powerful evidence for cosmic impact.
But their discovery raises many more questions.
- The supposed presence of nanodiamonds
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 nanodiamonds.
They may be graphite or graphene compounds
that kind of masquerade as nanodiamonds.
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.
ln the face of widespread skepticism,
a small group of impact researchers
claim that very recent cosmic catastrophes
have changed human history.
1 3,000 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 1 908.
lt 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 shockwave, the shocked air,
gets to super-high temperatures, and it radiates.
lt 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 1 3,000 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 1 0-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: ln fact, they are so potentially destructive
that when a very small meteor exploded in 2002,
it could have sparked a thermonuclear war.
- ln 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 lndia, 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 lndia.
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.
lt'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 31 2 A.D.
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 archrival, 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.
lnterpreting 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.
- lt'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 ltaly.
Have cosmic impacts
altered the course of human history?
lt's a question that provokes the world of astronomy
and even the world of religion.
ln the year 31 2 A.D.,
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.
lt 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.
ln 1 999, the team discovered a mysterious body of water
in the highlands of central ltaly.
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 manmade 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.
lt's been so overprinted by human activity,
and l 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 whammo 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?
lt'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 lmpact Working Group,
the answer is: far more frequently
than mainstream science currently accepts.
- So impacts over the course of human civilization
in the last 1 0,000 to 1 5,000 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-
l 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?