All language subtitles for The universe S07E07 When Space Changed History

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?