Original subtitles

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

throughout its more than four billion

years of existence planet Earth has

endured some extremely rough days

the very worst was it a shattering

encounter with a planet that got too

close

and anything been there it definitely

wouldn't have survived or a hot shower

of deadly rays that almost scoured the

planet clean of life the blast from the

impact would have laid waste a thousand

miles in every direction it's literally

the sound heard round the world

for a runaway volcanism that led to vast

extinctions to tiny microbes that

triggered a global deep freeze life has

teetered perilously close to the break

time and time again war life died then

than any time since and maybe any time

before this was the biggest and the

baddest of them all

are the darkest hours behind us or

lurking in the distant future

take cover as we count down the seven

worst days on planet Earth

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you may think you've had some really

rough days stuck in gridlock traffic

dodging a sea of humanity on the way to

work or trapped in a torrential downpour

or blizzard but they can't even begin to

compare to the seven worst days on

planet Earth

throughout its history Earth has

experienced some really bad days days

that have killed off life created life

restructured the planet as a whole

all of this together has formed the

earth that we live on today but during

those really bad days we certainly

wouldn't want to be here from our point

of view Earth has been through some

pretty rough days catastrophic impacts

that have really changed the face of the

planet and changed the makeup of the

flora and fauna the animals and plants

on the planet

one of Earth's worst days came early in

its history when an uninvited guest

barged into our neighborhood and

threatened to destroy the planet before

life had a chance to blossom

blasting in as the seventh worst day on

earth the Theia impact

about four and a half billion years ago

our solar system was a battle zone

giant boulders collided and coalesced to

form planets

infant earth took hit after searing hit

if we could somehow magically transport

ourselves back in time to be on the

early earth it'd be very interesting I

think to watch one of these large impact

events the surface of the earth itself

was probably heated to a near molten

state the atmosphere would be very dusty

it would be very hot so it'd be a very

alien world to us one that we actually

couldn't survive on just standing like

we are here today pounded by incoming

rocks earth slowly grew to nearly its

present size developing a solid crust a

thick mantle an iron core and a hot

stormy atmosphere some speculate that

life may have taken a tenuous hold but

then disaster

a neighboring planet named Theia had

been edging into Earth's orbital paths

the intrusion ended in the most

disastrous way imaginable a collision of

worlds was a very violent event you can

imagine something the mass of Mars about

ten percent the mass of the earth

lacking in from space and blowing all

this material in whatever was on the

earth at that time was radically changed

by this event

when a mars-sized object whacked into

the earth that was a bad day on earth

had anything been there it definitely

wouldn't have survived

it took hours for the full scope of the

catastrophe to unfold as the cores of

the two planets melded Earth's

atmosphere was blasted into space its

crust liquefied at over 2,000 degrees

Fahrenheit and vast portions of both

Earth's and theia's Mantle's were

ejected into orbit it's not at all like

what you see in the movies you can sit

down have a cup of coffee and it's still

going on these are you know big objects

take a long time to incur so these

aren't the normal flashes do you think

about a bullets hitting a wall

the plume of ejected material created a

vast orbital ring before coalescing into

a new companion for the earth the

newborn moon that fully fledged planet

merged with the earth iron cores would

have come together and the silicate

Mantle's were left on the earth and also

accreted into a disc that was orbiting

the earth

this disk most of it came back and

crashed back on to the earth but then a

portion of it reformed and over time has

been pushed out and has become the moon

it took about a hundred fifty million

years for earth to stabilize and it's

molten crust to reharden but although

the Theia impact was a very bad day on

earth it was a very good day for its

ability to sustain life when the moon

formed it's stabilized Earth's axis of

rotation otherwise gravitational tugs

from other planets would have caused it

to chaotically very and that would have

been bad for long-term climate stability

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what do we even have life as we know it

if that impact had not taken place

without a moon you could really have a

case where your tropics within hundreds

of thousands of years could rotate and

become the Arctic or the Antarctic and

you kill everything

with the impact over in the moon now

providing orbital stability the stage

seems set for a quiet future but that

was not to be before the plants you've

won the moon never is happy and all of a

sudden something terrible happens

earth was suddenly caught in the

crossfire

once again number six on our countdown

of worst days the late heavy bombardment

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approximately a hundred fifty million

years after the Theia impact the Earth's

crust cooled some speculate that early

oceans and even life may have evolved

but another Cataclysm would wipe the

slate clean

in the far reaches of the solar system

the orbits of the outer gas giants began

to fluctuate disrupting vast swarms of

asteroids and comets trillions broke

loose from their orbits and plunged

inwards toward the rocky planets

launching an era of fiery destruction

known as the late heavy bombardment

we know asteroids the size of Texas hit

the earth any impactor that big costs

the entire ocean to go away

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we sterilize the earth over and over and

over so the inference we have is that

life evolved over and over and over just

to be snuffed out again by these large

impacts the relentless bombardment

gouged out craters thousands of miles

wide and the hits just kept coming for

at least 200 million years

today billions of years of erosion and

shifting plate tectonics have erased any

trace of the Cataclysm from the Earth's

surface

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but it's a different story on the

cratered face of the moon we can see

very clearly its record on the face of

the moon the lava-filled basins were

formed during the giant impact events

that occurred during the late heavy

bombardment and so we know that large

objects hit the earth during this time

but this celestial rain of fire may have

had a silver lining

literally new evidence suggests the late

heavy bombardment

delivered precious metals to the surface

of Earth things like silver gold and

platinum

Earth's original store of these elements

had sunk into its molten iron core as

the planet slowly cooled but now with

our planet already solidified this new

supply of materials remained near the

surface able to be mined by future

humans today's technologies depend on a

lot of the heavy elements that were

delivered to the earth through impacts

so it may have been very difficult for

the life if there were life on Earth

during the heavy bombardment but it was

very good for the Earth's crust to have

all of these materials that we now

depend on delivered to the surface of

Earth through impacts the late heavy

bombardment was Earth's true baptism by

fire

but now as we reach number five in our

countdown of the planet's worst days

earth catches the worst cold in history

a climactic crisis so chilling that life

itself was in danger of being frozen in

its tracks

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both the Theia impact and the late heavy

bombardment turned earth into an inferno

but now as we continue our countdown of

the seven worst days on earth we skate

forward in time to a catastrophe not of

fire but of all-encompassing ice number

five on our countdown the frozen

Cataclysm known as snowball earth

we had these bad days and snowball earth

is much longer than a bad day is a bad

hundreds of thousands of years snowball

earth is that the planet that was a

snowball it cools enough that the oceans

freeze down to 10 feet 20 50 feet thick

imagine the Arctic sea ice we see now

except the whole planet has that during

a typical Ice Age glaciers invade the

temperate zones often reaching as far

south as modern New York or Paris but

during snowball earth but glaciers just

kept coming until they had encircled the

entire planet and frozen the oceans to a

depth of up to a mile

as average temperatures plunged to minus

75 degrees Fahrenheit the equator grew

is cold then as the South Pole is today

and this global deep freeze may have

happened not once but twice the first

episode beginning 2.4 billion years ago

during the snowball earth face the

entire earth has a climate quite similar

to modern-day Antarctica it's extremely

cold extremely dry extremely windy

extremely unhospitable

to life

the snowball earth hypothesis helps

explain the discovery of glacial

deposits than areas that were once at

the equator it's theorized that as the

glaciers marched on from the polar

regions they reflected sunlight back

into space and created a powerful

feedback loop turning the thermostat

relentlessly lower if the polar regions

get too large as the snow and highly

reflective ice coatings get too far down

in latitude they reflect more light back

into space the earth gets cooler the ice

goes closer and closer closer to the

equator so it's not to be kind of a

runaway processed ELISA is a freezer of

the earth but what caused the first

snowball earth scientists think the

culprit actually may have been life

itself

the gas that was most prevalent when

life first appeared on the earth was an

oxygen it was methane creatures at that

time single-celled bacteria would have

used methane as part of their normal

living processes

methane is a phenomenal greenhouse gas

so if you had a lot of methane in the

atmosphere you had likely very warm

temperatures

but 2.4 billion years ago a new group of

underwater microbes began absorbing

energy from the Sun in a process called

photosynthesis by converting carbon

dioxide and water into energy

photosynthesis polluted the earth with a

toxic new waste product oxygen vast

amounts of it

prior to 2.4 billion years ago oxygen

was a poison and any life that was on

earth did not use oxygen it was

considered a waste gas all of that life

that didn't like oxygen was exposed to

this rich oxygen environment and it

caused a great deal of stress

methane creatures were happy to live in

this oxygen free world and when oxygen

finally does appear it was like the

worst calamity in their history as

oxygen flooded the world it oxidized

methane turning it into carbon dioxide

the methane consuming creatures died off

been a fast extinction event called the

great oxygen catastrophe and as earth

lost its warming blanket of methane gas

the planet froze over

but if oxygen-producing life was the

primary trigger of the first snowball

earth that life now needed to find a

warm place to escape the disaster it had

caused

the earth at that time was even more

energetic tectonic Li than it is now the

formation of the earth produced enormous

heat that heat comes to the surface it's

slowing but back then many more

volcanoes around every volcano that

would have been this melted lake-like

zone where life could have thrived

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to show how volcanism could have carved

out cozy niches for life all you need is

a blowtorch and a big ball of ice

we're here at carving ice and ice house

owned by Roland Hernandez an amazing ice

sculptor who's created for us his

hemisphere of solid ice which represents

snowball earth we've placed it up here

on this dolly so that we can heat it

from below with an industrial blowtorch

to represent the type of heating that we

would experience on snowball earth from

volcanism deep beneath the surface

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scientists suspected the extreme heat

pressure generated by volcanism beneath

the earth's surface would have created

cracks in the ice for life to take

refuge

[Applause]

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okay so you can see how the cracks have

formed all throughout the ice along the

top here these are very similar to the

types of cracks that would form during a

snowball earth event it's in these

cracks where you can get the mixture of

a little bit of liquid a little bit of

heat a little bit of chemistry in other

words the perfect ingredients for

generating an environment where life can

take root and even thrive volcanism

wasn't just key to life survival during

snowball earth

it also may have forced the glaciers to

finally retreat so you've got all of

these gases that are coming out of the

volcanoes things like water vapor carbon

dioxide sulfur dioxide for example which

are escaping into the atmosphere and

over time over tens of millions of years

you're building up these levels of

greenhouse gases at some point is going

to get so warm in the atmosphere that

the ice begins to melt both episodes of

snowball earth

the first 2.4 billion years ago and the

second 600 million years ago placed

profound stresses on early life but

oddly both were followed by enormous

flowerings of new species we know from

the sedimentary record that just before

animals bloomed into existence an

enormous amount of phosphorous came into

the ocean there are big rocks of

phosphorous they eroded as that erosion

occurred phosphorous levels in the ocean

rose all of a sudden life is able to

just bloom this may have really caused

the diversification two times on the

microbial world of 2.3 billion years ago

but more importantly to us it really

probably helped the diversification of

animals at 600 million years ago

although snowball earth produced some of

the planet's harshest weather life not

only managed to survive it bounced back

stronger than ever which is why this

disaster only ranks as number five on

our list of worst days but as the

countdown continues forensic evidence is

finally emerging that just may explain a

far deadlier Cataclysm a mass killing

spree that stands as the oldest murder

mystery on the planet

so far on our countdown of the seven

worst days on earth

we've seen our planet battered during

the moon-forming impact

baked by the late heavy bombardment and

almost completely frozen over by

snowball earth now we travel forward

over a hundred million years as the

world is rocked by one of the greatest

mass killings in its history number four

on our list the Ordovician extinction in

the billions of years of life on Earth

99% of all species that ever lived have

ultimately vanished mostly due to five

mass extinction events

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the first was during the Ordovician

period 450 million years ago the mass

extinction during the Ordovician is the

most mysterious of the so-called big

five simply because it was the one that

was the oldest everyone after that was

closer to us in time and the further

back in time you go the more fuzzy our

scientific view of the past is during

the Ordovician period the globe was

covered with three major oceans and four

super continents

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the land was still barren but the oceans

teemed with life including brilliant

corals and the planets first fish then a

mysterious Cataclysm swept the seas and

60% of life on Earth vanished there's a

couple of possibilities number one it

got cold again so why would have gotten

cold well it could have been that plate

tectonics moved all of the formerly warm

continents down to the polar regions and

that dropped the temperature of

everything for years scientists blamed

the Ordovician extinction on a

devastating ice age but now some

researchers propose that the mass killer

could have been something from the

cosmos like a gamma-ray burst the

biggest blasts in the universe

a gamma-ray burst is a colossal

explosion of a star that occurs

asymmetrically there are two oppositely

directed beams of very energetic

high-speed particles and radiation that

goes zipping through space kind of like

a laser beam if that beam is aimed right

at earth that can cause significant

damage here a large burst would vaporize

a third of a planet's protective ozone

layer and creatures on the side of the

earth facing the onslaught would suffer

lethal radiation exposure

the destructive energy of a gamma-ray

burst can be demonstrated here on earth

here's our globe representing the earth

at the end of the Ordovician period a

time when one group of scientists thinks

that a gamma-ray burst may have

triggered a mass extinction the paper

represents the Earth's ozone layer and

the gamma-ray burst is represented by

this propane torch

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and seconds worth that's all they say it

would take to destroy about a third of

the Earth's ozone so of course the gamma

ray burst didn't actually torch the

earth but it did destroy the ozone that

it encountered and it would have messed

with the chemistry of the ozone

molecules on this side of the globe and

when the ozone was destroyed UV

radiation can penetrate to the surface

and the ultraviolet radiation is very

lethal to life it's very destructive to

DNA so it may be that a gamma-ray burst

destroying the ozone layer contributed

to or maybe even triggered a mass

extinction at the end of the Ordovician

in addition to depleting the ozone layer

a large gamma-ray burst

also could have ripped apart nitrogen

and oxygen molecules in the atmosphere

producing a gaseous smog of nitrogen

dioxide that blocked sunlight and set

off a secondary disaster an ice age

it's not clear whether that could have

been caused by a gamma-ray burst but at

least part of the Ordovician extinction

seems to have been marked by a huge

decrease in the number of surface

dwelling creatures like on the Earth's

surface or in the surface layers of the

ocean that may well indicate that it was

ultraviolet radiation that killed him

off rather than some other factor a

gamma-ray burst could be one explanation

for the first mass annihilation of life

on Earth but a startling new hypothesis

points to a different cosmic force a

bizarre and potentially deadly

phenomenon known as a bow shock

a bow shock forms when there's

compression of material in front of a

moving object so for example if you have

a boat zooming along it creates a way

the compression in front of it that then

bends around as the boat canoes through

well our galaxy is moving rapidly

through space so it can compress

intergalactic gas in front of it heating

it up creating cosmic rays and some of

those cosmic rays can then hit the earth

our solar system oscillates through the

Milky Way traveling above and below the

main disk of the galaxy every 64 million

years once outside the galaxy's

protective magnetic field our planet is

vulnerable to deadly cosmic rays

generated by the Galactic bow shock much

like a wakeboarder on a lake

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wakeboarding would be a reasonable

example of a bow shock in space

while the wakeboarder is well within the

confines of the bow wake of the boat the

water is very calm and smooth and he has

no trouble standing up but during those

periods when he moves out towards the

edge of the way the water becomes a bit

more turbulent and a bit more chaotic

and he has trouble standing up

the same thing is true in space for most

of the time the earth and Sun are well

within the protective confines of the

Milky Way galaxy's magnetic field

protecting it from the cosmic rays and

other radiation that's coming in from

the bow shock but during those periods

when the Earth and the Sun rise above

the Galactic plane it's much more

vulnerable to all of these cosmic rays

coming from the bow shot fossil records

indicate that the biodiversity of many

species may increase and decrease than

62 million year cycles those cycles

closely coinciding with the times of

greatest exposure to cosmic rays from

the Galactic bow shock which occur every

64 million years could the two events be

connected to of the mass extinctions

happen to have occurred at about the

time when the Sun was highest above the

plane of our galaxy that suggests that

there's something about that particular

location that's special causing these

mass extinctions

during the Ordovician extinction earth

could have been blasted with enough

deadly radiation from the Galactic bow

shock to unleash genetic mutations and

DNA damage that wiped out over half of

all species

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this is not yet a well-tested idea it's

just out there on the drawing board but

it could explain some of the possible

periodicity in Earth's mass extinctions

but while the Ordovician extinction was

fatal to most species some grasped at

the opportunity it's like pulling weeds

out of a garden you sort of clean out

and weed out and thin out that seems to

have happened in the Ordovician mass

extinction some creatures which died out

allowed others to diversify the

Ordovician was the first mass extinction

but hardly the worst

number three on our countdown of the

worst days on earth it's the most famous

die-off in prehistory but if you think

you know what killed the dinosaurs you

may be in for a surprise because some

scientists now argue that the common

explanation of a single giant impact on

a single disastrous day is itself about

to be blasted away

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in our countdown to the very worst day

on earth

no catastrophe has been the subject of

more public fascination and sensational

headlines than the bombardment that

ultimately cleared the path for mankind

but today controversial new hypotheses

challenge the concept that a single

disastrous impact wiped out the

dinosaurs and led to the third worst day

on earth the KT extinction

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sixty-five million years ago we would

have seen a world something like Africa

in terms of the number of animals out

there but instead of big mammals we have

big dinosaurs herds of Triceratops herds

of duck-billed dinosaurs small to big

predators the largest being t-rex

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dinosaurs ruled the prehistoric world

for almost 200 million years then

something took out two-thirds of all

living creatures including the giant

beasts after years of searching for

clues most experts now agree that a

single Cataclysm doomed the dinosaurs

the evidence for an impact of a

six-mile-wide asteroid 65 million years

ago is about as good as anything gets in

science 65 million years ago a rock the

size of Mount Everest barreled down from

the sky and slammed into the Yucatan

Peninsula near modern Chicxulub Mexico

the impact unleashed an unstoppable

chain of destruction first locally then

across the globe

the Katy is an asteroid driven

extinction a big rock from space came

down clunked a few dinosaurs on the head

but the kill mechanism was really the

secondary effects of this it would have

been dark into the atmosphere acid rain

a change in the entire biosphere

proponents of the single impact Theory

point to a convincing array of evidence

including high levels of the asteroid

element iridium at the KT events

geological boundary or death layer and

of course The Smoking Gun itself the

underwater crater in modern Mexico but

is this cold case finally closed some

scientists now argue the Yucatan

asteroid had accomplices there seem to

be various causes that can trigger these

and in some cases several causes come

together and sort of a confluence of bad

circumstances to provide a particularly

damaging extinction event millions of

years before the KT extinction vast lava

flows had been pouring out of the Deccan

Traps a series of lava beds now located

in Southwest India

these flood basalts once spewed out

enough magma to cover a million square

miles and belched up a toxic brew of

gases that could have altered the

climate around the world that period of

eruption is pretty coincident with the

extinction 65 million years ago as well

in fact they were going on for millions

of years before the KT impact and before

the extinctions and so perhaps could be

a complicating factor in this scenario

the dinosaurs received a double knockout

blow

first the rampant volcanism of the

Deccan Traps then the Yucatan impact

and a small group of dissenters goes

even further claiming that multiple

asteroids struck earth at roughly the

same time 65 million years ago according

to them the Yucatan impact wasn't the

largest only the best documented

some people think that there may have

been multiple impacts a shower of

impacts for example perhaps they came

from a single object that broke apart

supporters of this hypothesis point to a

suspicious geologic feature a 370 mile

Basin off the coast of India more than

three times larger than the Yucatan

impact site but controversy swirls

around this so-called shiva crater named

after the Hindu god of destruction

including whether it's even a crater at

all while this feature certainly looks

circular and looks crater like there's

no other evidence that it's an actual

impact structure for some the dinosaur

die-off debate rages on but most

scientists agree the apocalyptic event

was a very fortunate day for small

mammals that were no longer dinner for

t-rex had it not been for the KT impact

and the volcanism that was also at the

time of the extinction of the dinosaurs

the mammals probably wouldn't have risen

to the prominence that they did and

thank heaven for the rise of mammals

because that led to the rise of humans

the KT extinction raises a sobering

question could humans one day go the way

of the dinosaurs

that's what viewer Tom Moore from Adrian

Michigan wanted to ask the universe will

earth be struck again by a KT sized

asteroid well Tom earth could definitely

be hit by another KT size comet or

asteroid they're out there the good news

is we're tracking the positions of most

of the big ones so if we ever find one

with Earth's name written on it

hopefully we'll be able to deflect it

before it reaches Earth the KT event

toppled t-rex

but it only ranks as number 3 on our

countdown of worst days on earth number

2 was the mother of all extinctions the

greatest die-off that life on Earth has

ever suffered it's also been one of the

biggest unsolved mysteries in science

until now

as we near the climax of our countdown

we reopen one of the oldest cold cases

an unsolved murder mystery that happened

250 million years ago almost 200 million

years before the downfall of the

dinosaurs the second worst day witnessed

the greatest mass extinction in the

planets history a cataclysm known as the

Great dying

during the Permian period earth was a

wondrous world of mammal-like reptiles

and exotic sea creatures then 90% of all

life disappeared from the planet this is

a bad few hundred thousand years on

planet Earth

but it was certainly the most

catastrophic more life died then than

any time since and maybe any time before

this was the biggest and the baddest of

them all for decades scientists have

sifted through Clues struggling to solve

the mystery of the great dying when the

survival of life itself

seemed to hang by a thread

one of the prime suspects a supervolcano

that tourists Siberia opened for

hundreds of miles

erupted for at least a million years and

produced the greatest lava flows ever

known enough to bury the entire United

States thousands of feet deep

this wasn't a single giant volcano it

was simply cracks in the earth and

you're like pumping out lava it's like a

fire hose spewing lava everywhere well

that's certainly what killed anything in

his way it's believed that you had these

beds of coal on what is now Siberia

which can have lava erupting underneath

them burning the coal putting all sorts

of noxious greenhouse and other toxic

gases into the atmosphere and really

putting strong stress onto the biosphere

the increased global warming was fatal

to most animals but plants usually

thrive on carbon dioxide so why did they

also succumb at rates that have never

been equalled

there's a second killer in the story

that we think and just now discovering

and that's the presence for the first

time on the planet of massive amounts of

hydrogen sulfide gas the same stuff you

see with rotten eggs that's a true

poison and it with the heat combined I

think to caused this greatest of mass

extinctions

if the scientific jury is still debating

the cause of the permian-triassic

extinction no one disputes that those

were the darkest days for life on our

planet so far but life on Earth cannot

and will not survive an event that

scientists predict is as unavoidable as

death itself the number one worst day on

planet Earth the solar apocalypse

in five billion years our Sun will reach

the end of its life

as it exhausts its nuclear fuel it will

undergo a disastrous transformation

bloating into a red giant star 200 times

its original size as it swells it will

first engulf Mercury then Venus the

incinerated earth will either be pushed

to a higher orbit or swallowed itself

the good news humans won't be around the

day our Sun incinerates service the bad

news we will have been roasted

long before

the Sun gets brighter about 10% every

billion years and so in less than a

billion years the Sun will be bright

enough that's predicted that it will

pump basically all well most the carbon

dioxide out of the atmosphere and so

things that rely on carbon dioxide like

plants are going to have a hard time

surviving in a natural order as plants

shrivel and oceans evaporate biologists

predict a future make a mass extinction

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the age of animals will end in about 500

million years we have as much time in

the future to be alive as an animal as

we've had in the past or halfway through

that's a sobering thought

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we've seen earth smacked by the giant

moon-forming impact strafed and

sterilized during the late heavy

bombardment and frozen into a giant

snowball

a cosmic force ravaged an ancient water

world during the first mass extinction

followed by a near total extinction

during the great diamond

and the spectacular fall of the

dinosaurs

what else lies in store before our

planet is ultimately baked by the Sun

earth will certainly continue to

experience disasters all the way up

until the very end

when the Sun spread giant phase brings

an end to the story history has proven

that Earth is an unpredictable planet

orbiting in a very dangerous galactic

neighborhood to survive mankind must

learn from the worst days of our past

and try to prepare for whatever the

cosmos might throw at us only by

increasing our knowledge of the universe

and we hope to thrive and fully enjoy

our final 500 million years of life on

Earth

you