NARRATOR: In the beginning,
there was darkness. And then, bang-- [explosion] --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 wrought with catastrophic moments
when space changed history. [theme music] [thunder roars] 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? BRUCE MASSE: 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: Archeologist
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 human history. [explosion] [wind gust] [music playing] 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. BRUCE MASSE: 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 byproducts, 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 its head. In Hindu, it's a fish with
a giant horn on its 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, its 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 deepwater ocean impact of a comet. LUCIANNE WALKOWICZ:
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 and 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. LUCIANNE WALKOWICZ: A comet
coming in from outer space would be carrying with it an
immense amount 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 a 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 Burckle Crater
in honor of a colleague at Columbia University. Burckle is a massive depression
located nearly 1,000 miles off the coast of Madagascar. About 18 miles in
diameter, Burckle 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 in 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
the 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 Burckle 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 field work 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. [music playing] NARRATOR: But when Dallas
Abbott traveled to Madagascar, she found surprising evidence
trapped inside the dunes. DALLAS ABBOTT: 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
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 Burckle 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. [music playing] In the search for
extraterrestrial impacts that have changed
history, certain facts are not in dispute. [horse neighs] 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. MARTIN MORGAN: 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. DALLAS ABBOTT: 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 in California shows the unmistakable signs
of dramatic global cooling. MARTIN MORGAN: 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-- [explosion] --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 mega tsunami. One set of chevrons is
located in Australia's Gulf of Carpentaria. DALLAS ABBOTT: 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 crater's 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 that the
event was about 1,500 years ago. And I knew about this
climate event at 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 match 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. [explosion] DALLAS ABBOTT: 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, you
know, settles out. NARRATOR: For a cosmic
impactor 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 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
going to explode and make a huge crater. [explosion] 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 seemed 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? [music playing] 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. So 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. [explosion] MARK BOSLOUGH: 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 edge 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. MARTIN MORGAN: 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: Archeological
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. MARTIN MORGAN:
There was a moment where the population of
megafauna in the Americas changed. The megafauna 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 climatic u-turn,
especially one hypothesis that places the blame
squarely on outer space. The Clovis centers were having
to adapt to new conditions. And one of those changes
could have been a comet impact over the laurentide ice sheet. [dramatic music] 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 ocean currents and
triggering the Younger Dryas cooling period. Ken Tankersley, a University
of Cincinnati anthropologist, uncovered cosmic impact
evidence in Sheraton Cave in Northwest Ohio. KEN TANKERSLEY: The
layer which we found here is known as the black mass. 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,
seeming indisputable evidence for a larger cosmic impact. KEN TANKERSLEY: We have
what's called impact diamonds. Impact diamonds or
shattered diamonds occur when some type of
explosion or sudden impact occurs with the Earth's surface,
compressing carbon material to create these impact diamonds. NARRATOR: Also
called nanodiamonds 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 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 huge
physical piece of evidence-- an impact crater. [explosion] 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. [mysterious music] 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 is 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 airburst. ALEX FILIPPENKO: An airburst
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 airburst is the Tunguska event
over Siberia in 1908. It leveled 2,000 square
kilometers of forest, but there's no impact crater. MARK BOSLOUGH: 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 shock air gets two 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. [explosion] NARRATOR: Even a smaller
Tunguska-sized meteor around 200 or more
feet in diameter can produce an airburst
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 airburst. 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. BRUCE MASSE: Now, an impact
like the Tunguska event-- a 10 megaton airburst, say,
at 5,000 meters over New York City-- if that were to
happen today, would lead to the deaths of
almost a million people, another several billion
people injured, and a couple of trillion dollars of damage. So even airburst 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 airburst, an explosion up there. MARK BOSLOUGH: And this
was an enormous explosion over the Eastern Mediterranean. It was observed by satellite. This was unusual to be over
a relatively populated area. NARRATOR: At the time of the
airburst, 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 cataloged. 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 on to 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. MARK BOSLOUGH: Constantine
was a Roman emperor famous for a number of things,
not the least of which was his conversion to Christianity. Constantine's adoption
of the Christian religion in the fourth century
is instrumental and 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. [bell ringing] But some believe Constantine's
vision has an astronomical explanation. MARTIN MORGAN: 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. [music playing] 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. MARK BOSLOUGH: What you
would see, of course, it 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. [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 II. There's ordnance 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 over printed
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-o type impact there. NARRATOR: Cosmic impact or
not, Constantine's vision is considered one of
the most pivotal events in human history. MARTIN MORGAN: 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. [bell ringing] 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 are 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. [dramatic music] 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? [explosion]
