All language subtitles for How the Earth Was Made HC 720p HDTV S01E10 Asteroids EN

Earth, a 4.5- Billion-year-old planet,
still evolving.

As continents shift and clash, volcanoes
erupt, and glaciers grow and recede,

the Earth's crust is carved
in countless fascinating ways,

leaving a trail
of geological mysteries behind.

This episode investigates one
awesome force that shapes the Earth.

It's extraterrestrial, and it doesn't happen
over millions of years, but in seconds.

It's a force caused by an immense
impact from asteroids -

giant rocks from space.

The investigation of asteroid strikes
has given scientists insight

into the formation of the universe,

providing a window
into planet Earth's ancient past.

There is a giant hole in the Arizona
desert, 35 miles east of Flagstaff.

It's huge, three quarters
of a mile wide and 550 feet deep.

The Washington monument
could fit inside it.

The mystery confronting geologists
in the late 19th century was,

how did this happen?

People agreed that only a massive force
could have created such a huge chasm.

But what was this force?

The most likely theory was
that a huge volcanic explosion

had ruptured the rugged landscape.

Scientists had discovered similar sized
craters in volcanic areas before.

But Grove Gilbert, chief geologist for the
US Geological Survey, had another idea,

one that came to him after
observing craters on the moon

through his telescope.

He saw similarities
between the moon's craters

and the mysterious hole
in the Arizona desert,

leading him to speculate that the
Arizona crater might have been caused

by an asteroid impact.

But this was just a theory.

At the time, no-one had proven
that any crater on Earth

had been caused by an asteroid.

So, in 1892, Gilbert decided to travel
to the mysterious Arizona crater.

He wondered if this could
have an impact origin,

or alternatively, a volcanic origin.

And so he had these two competing
hypotheses that he wanted to test.

Gilbert assumed that if the crater
was caused by an asteroid,

he should find a giant,
alien rock in the middle of it.

But there was none.

But he did see what he thought were
signs that a volcano might be the cause.

KRING: When Gilbert arrived,
he realised that this hole in the ground

was associated with
some volcanic peaks in the distance,

you can see them
in the background over the rim,

or beyond the rim of the crater,

and so, immediately, I think,
he was prejudiced, if you will,

towards a volcanic,
as opposed to a meteoritic origin.

Not far from the mysterious crater,
Gilbert found another, similar, giant hole.

He declared this one as an unusual
volcanic crater, called a maar.

He knew that four years before,

in Japan, scientists had witnessed
the formation of a maar

after a huge underground
explosion of steam.

The resulting crater resembled
the giant hole Gilbert came across

in the Arizona desert.

They are produced when basaltic
magma rises through the Earth's crust,

encounters groundwater, creating
a steam explosion, which causes a blast

that produces craters like
the one, uh, over my shoulder.

Intriguingly, the two almost identical
craters were only 50 miles apart

in the same desert.

One was known to have been caused
by an underground steam explosion.

Because of their close proximity,
Gilbert concluded

that the mysterious crater
was also caused by volcanic activity.

In 1896, he published his findings
in an influential report

and, for the wider geological community,
the debate was resolved.

But, six years after Gilbert's findings,

American entrepreneur
and mining engineer Daniel Barringer

arrived on the same scene.

He was intrigued by mysterious
small iron rocks shepherds had found

around the crater
while grazing their herds.

Barringer was convinced that Gilbert
was wrong about the crater's origins.

I'm holding in my hands a fragment
of what started it all.

It is not the type of material that one
finds in any other geological terrain

or created by any
terrestrial geologic process.

Iron in rock is usually mixed
with other minerals.

But at the mysterious crater,
the iron was almost pure.

And there were large amounts, normally
not found on the earth's surface,

spread over a huge area
surrounding the crater.

Barringer believed the pieces
found here were meteorites,

small space rocks that form
when big asteroids break apart.

He had a hunch that this huge
hole in the desert was formed

by a giant asteroid
made largely from iron.

Barringer immediately
saw the commercial opportunities.

From the crater's size,

he calculated that the asteroid
must have weighed ten million tons.

With iron then at $80 a ton,

Barringer was convinced he could
become a rich man from mining the iron.

So in 1903, Barringer bought
the crater site of over 1,200 acres

and hired crews to begin digging.

Convinced it was an impact site,
he named it Meteor Crater.

KRING: We're in one of the remnants
of Barringer's mining camp.

This is a place where
his miners lived, ate, slept,

while they looked
for the buried meteoritic mass

that they thought was
beneath the floor of the crater.

For years, Barringer and his men
found only small fragments of iron.

Undeterred by this, they kept
digging deeper shafts into the earth.

KRING: The largest of which,
the main shaft, you can see

is a white island of debris
in the centre of the crater.

In fact, one of those holes close to me
here reached a depth

of nearly 1,400 feet beneath the surface
of the Earth.

In all of these cases, or most of
these cases, they found telltale hints

of the impacting meteoritic body,
but no giant mass.

Barringer did stumble across
some clues, however.

Strange and unique rock formations
such as fine, pulverised rocks

spread around the crater.

He noticed, quite rightly, that it is so fine,
it is almost like talcum powder,

the type of thing that immediately
alerted him to something unusual,

in the geologic processes
that shaped the land here.

To Barringer, the pulverised
rock was a major clue

that pointed to one thing,
the violent impact of an asteroid.

As a geologist, if I saw this rock
I would say, "OK, this is not something

"that I see around a volcanic crater,
there's something going on here.

"And... and I need to figure it out."

Barringer also discovered other oddities.

At the crater rim, he noted a bed of
rocks that were chaotically overturned.

Dramatic energy uplifted the rocks
in the crater wall behind me.

Originally they were absolutely horizontal

and you can see
that they are tilted upwards,

and if you look very closely,

at the very top of the rim,
they are completely overturned.

For 27 years, Daniel Barringer
obsessively sunk mining shafts

in search of his giant iron asteroid,
with no success.

Barringer died in 1929,

having lost 600,000
of his own and investors' money -

ten million in today's dollars.

The privately owned crater has
remained in his family to this day.

But his theory about the asteroid impact
at Meteor Crater

spurred further investigation

based on three clues he had uncovered.

The first, the pieces of pure iron
scattered across the crater.

Next, rock that had been
crushed into fine powder.

And finally, strange rocks thrown up
and flipped over at the crater's rim.

Interestingly, even though
Barringer hadn't convinced

the geologic community
about the impact origin of this crater,

he had launched at least
a small number of people

into an investigation
of impact processes.

Proof of Barringer's asteroid
theory would get a boost,

some six decades later,
from an unexpected source.

Meteor Crater in the Arizona desert
was still a mystery

to the geological community.

The debate on whether it was caused
by volcanic activity or an asteroid impact

wasn't resolved until 1960.

A young geologist, Eugene Shoemaker,

became interested
in Barringer's research.

He would take the investigation
in a new direction,

which turned Meteor Crater

into one of the most investigated
crater sites on Earth.

Shoemaker was working on craters
left by nuclear explosions

on test sites in Nevada.

His task was to find out how the
explosions transformed the landscape.

Intriguingly, at the test sites,
he found the exact same rock formations

Barringer had described at the
mysterious Meteor Crater in Arizona.

Shoemaker passed away in 1997,

but his wife, astronomer
Carolyn Shoemaker, recalls his findings.

Gene compared Meteor Crater

with the craters that he had been
mapping at the Nevada test site.

At the test site,
Gene saw overturned beds also,

near the top of the craters in the rims.

And that... that certainly told him
that there was a strong similarity,

because they were so obvious
at Meteor Crater.

Shoemaker came upon
another important clue

that linked the Nevada test sites
to Meteor Crater.

He found this samples
of this very unusual rock.

This was once sandstone,
but he recognised it had been altered.

In the craters left by explosions
from nuclear bomb testing,

Shoemaker discovered
crystalline structures -

the same structures found
at Arizona's Meteor Crater.

Today we understand that this
is shocked sandstone glass,

that is, the original sandstone,
all of the quartz crystals were melted

and put into a frothy, bubbly,
glassy matrix which we have here.

They were caused

by the incredible energy released
in the shockwaves of a nuclear blast.

For Shoemaker, it was conclusive
proof that the vast Meteor Crater

wasn't formed by volcanic eruptions.

Instead, it was created by a powerful
asteroid impact in just a split second.

The shocked rock also gave scientists
a clue about the age of the crater.

When an asteroid hits the Earth,

the energy from the blast
is absorbed by the surrounding rock.

Using a process called
thermoluminescence dating,

scientists are able to measure
the amount of energy

the rock is giving off in the form of light.

The shocked rock
from Meteor Crater told them

that the impact happened
50,000 years ago.

But for some, there remained
one problem with this theory.

If the Arizona earth was crushed
by a huge asteroid,

where was the rock
that made the impact?

Scientists had a hunch
that when it struck,

the iron meteorite had vapourised.

Conclusive evidence came in 1997
when scientists were able to simulate

the impact using
advanced computer modelling.

From the size of the crater,

they calculated that the asteroid must
have weighed at least 300,000 tons

when it struck.

The data further revealed that it hit Earth

at a speed of over
25,000 miles per hour.

That's 35 times the speed of sound.

Upon impact, the asteroid
triggered a massive shockwave

many times more powerful
than a nuclear explosion.

Within a matter of seconds, this impact
crater behind me was excavated,

and this debris was, uh,
deposited on the landscape.

Within seconds, the shockwave

and the very high velocity air blast
radiated across the landscape.

The shockwave travelled back
up through the asteroid's iron core,

vapourising most of it, and scattering
the rest in small pieces over a wide area,

up to six miles away.

The energy that produced
this crater ranges somewhere

from a few hundred to perhaps
a thousand times greater

than the energy that destroyed the cities
of Hiroshima and Nagasaki

in World War II.

The investigation has uncovered
reasons why there are no big remnants

of asteroid rock in the Arizona crater.

Crystalline structures
in the rock showed evidence

of a strong shockwave
that followed the impact.

Computer modelling revealed that
the speed and size of the asteroid

created enough energy
for the rock to vapourise when it hit.

This crater is particularly important
because it is the youngest

and most pristine impact crater
on the surface of the Earth.

It was also the first recognised impact
crater on the surface of the Earth,

and so it is in some sense
the Rosetta site.

It is the touchstone for geology.

It is here that specialists from around
the world come to study and learn

about impact cratering
as a geologic process.

Since 1960, when Shoemaker proved
that Meteor Crater was an impact site,

geologists went looking for more.

Armed with this new information

and the developments in space
and satellite technology,

they would revolutionise
our understanding

of how asteroids have shaped
the surface of the Earth.

Once the Meteor Crater in Arizona

proved an iron mass can burst from
space and create a monster chasm,

scientists began to search for others.

They questioned whether some craters
they thought of as volcanic

were in fact caused by asteroids.

The investigation turned to
Sudbury in Ontario, Canada.

There is no obvious crater
but, for over 150 years,

the city has been the centre of fabulous
mining wealth and a geological mystery.

3,000 feet below ground
in one of Sudbury's mines,

thick veins of copper and nickel
are on view.

Until recently, these mining riches
were associated with volcanic activity.

One of the really distinctive
features of Sudbury is the fact

that it has world class metal
deposits associated with it.

And originally, these were thought
to be related to volcano activity,

volcanic activity and magmas
coming from inside the Earth,

bringing ore and metals
from the inside out.

But something didn't add up.

When scientists investigated
the rocks around the mine,

they were surprised.

None of the outcrops were typical of
the types of rock created by a volcano.

To geologists, it was a hint
that the copper and nickel treasures

below the surface were formed
by a different process.

They were stumped

until they came across Eugene
Shoemaker's work on Meteor Crater.

It made them wonder whether this
vast mine could also have been formed

by an asteroid impact.

Could the vast reserves of copper
and nickel have arrived from space?

Rocks above ground
reveal new evidence.

What we have is a conical type fracture
system with these lineations or lines

running through them, and they...
they focus down into a point.

These deformed rocks
are called shatter cones.

Spray is convinced that the only force
powerful enough to deform a rock

into a shatter cone like this
would be an asteroid impact.

And these are formed

due to the shockwave
interacting with the target rocks,

and they compress the rocks,
just like, uh, compressing a spring,

and then,
when the shockwave releases,

they form these conical-like structures,
which are beautifully shown here.

So these are diagnostic of impact,
we can't form them any other way,

you can't form them with dynamite,

you can't even form them
with nuclear weapons.

But shatter cones were only a hunch.

Another clue came from
the composition of the rock.

It's a mixture of violently broken pieces,
fused into melted material.

So what we have here is made up
of the debris from the Earth's crust,

blasted into millions of pieces,

and the darker core material
may well contain traces

of the meteorite left in it
in the form of iridium.

Iridium is one of the rarest metals
on the surface of the Earth.

In space, it is a thousand times
more abundant.

Asteroids are like space rubble, and
their composition varies dramatically.

Some are made of rock-like material,
some from metals such as iron,

but they all have one thing in common.

They all contain comparatively
large amounts of iridium.

So any high amounts of iridium
found on Earth

becomes a fingerprint
of an impact event.

So what we're going to do
is take a sample and analyse it,

to see if we can find
an enriched iridium signature,

which would tell us that we have
a particular class of meteorite.

To find iridium, the lab samples of the
crushed rock are heated in a furnace

to over a thousand degrees Celsius.

The rock melts and metals in the
rock separate out and form a disc.

When the disc cools,
it is analysed for traces of iridium.

Hi, John. How's it going?
Not so bad.

Metal from the rock
is dissolved into liquid.

It is passed through
a mass spectrometer

capable of spotting tiny metal parts.

This incredibly accurate device
provides the vital piece of evidence.

The blue and red lines show there's ten
times more iridium in the Sudbury rocks

than in control samples
from normal earth crust.

This is indisputable proof that Sudbury
had once been hit by a huge asteroid.

But where was the impact crater?

The landscape here is flat
as far as the eye can see.

Scientists believe over millions
of years, the crater disappeared.

Erosion wore it down until all that is left
is the faint outline of ring structures

seen on satellite images from space.

Spray and his colleagues
have surveyed the area

and found that Sudbury is
the second biggest impact site on Earth.

155 miles in diameter,
that's three quarters of the size

of the world's largest crater
at Vredefort in South Africa.

Spray calculated almost
two billion years ago,

a space rock the size of Mount Everest
must have crashed into Earth here.

When the asteroid hit
it produced an instant crater

20 times deeper than
the Grand Canyon.

The energy is so intense with
the shockwave going back up

through the projectile, the back flows off,

and you end up fragmenting
the projectile, the meteorite,

such that you may even end up
with pieces of the Sudbury projectile

on the moon, and that's highly likely.

So it actually gets blasted out into space.

But one question remained.

Where did the valuable reserves
of nickel and copper come from

that turned Sudbury
into a famous mining site?

The asteroid had vapourised,

so the large nickel and copper deposits
couldn't have come from space.

When the asteroid hit, it penetrated
almost 18 miles into the Earth,

melting a huge cavity into the rock.

Scientists estimate that this giant hole
lasted only a short while.

Within hours, it collapsed,
because of gravity.

It's just like when you try and dig a hole
on the beach in sand with your shovel.

You're spading the sand out
and you can only go so big

before the sides actually collapse in.

After the cliffs collapsed,

the crater floor filled up
with a deep lake of hot, liquid rock.

The hole had been created in seconds,

but the hot rock took hundreds
of thousands of years to cool.

During this time, heavier metals
like copper and nickel

naturally present in the liquid rock,
sank to the bottom

and formed Sudbury's deposits
of precious minerals.

The impact at Sudbury had radically
changed the geology of a wide region,

concentrating nickel and copper
into awesome mining deposits.

Impact sites were now
more than academic interest.

Such rich mineral deposits
potentially meant big business

and economic wealth.

Mining companies on the hunt
for precious natural resources

now use satellite imagery to reveal
new craters around the world.

Rings that can be seen from space
suggest giant asteroid impacts.

They know that these impact sites

may contain more than
just copper and nickel.

Rich gold mines in South Africa
were also thought to have been created

by volcanic processes,

but the discovery of shatter cones
in the 1960s and ring structures

seen on satellite images revealed

what is now thought to be the
biggest impact crater on the planet.

Here, the impact concentrated
valuable minerals in the rock,

this time into precious deposits
of gold ore.

And at Chicxulub, Mexico,

scientists discovered traces
of a large asteroid impact

that wiped out the entire dinosaur
population 65 million years ago.

But recently,
scientists have drawn a link

between the massive crater at Chicxulub

and a huge oil reservoir
discovered nearby.

As the asteroid crashed
into the Earth's crust,

it fractured the underground rock,
making it porous.

Oil, abundant in the deeper layers below,
rose up and seeped into the porous rock,

creating an oil reservoir.

Now scientists could more easily
recognise signs of large impact sites.

Shatter cones were evidence
of strong shockwaves.

The presence of the space metal iridium
was proof for an asteroid impact,

and satellite imagery has shown
how impact craters

can be linked to vast mineral wealth.

Besides the minerals found
at different impact sites,

asteroids have left evidence
of massive destruction.

And this has led scientists
to a terrifying conclusion.

If it has happened in the past,
there is little doubt it could happen again.

October 9th, 1992.

Johnstown, Pennsylvania.

Thousands of sports fans were watching
their local high school football game

when a dazzling meteor
slashed through the skies.

In only a few seconds it travelled over
Eastern Kentucky, North Carolina,

Maryland and New Jersey.

It became one of the most filmed
fireballs in history.

When it landed in Peekskill, New York,
it smashed the trunk of a car.

Luckily, no-one got hurt.

November 20th, 2008,
an asteroid struck Earth again.

A mighty fireball streaked
over Western Canada.

As it dashed through
the skies of Alberta,

it broke into thousands
of little pieces.

It is the greatest number of fragments
recorded from a single fall.

Each year,
almost 4,500 small sized meteorites,

greater than two pounds each, hit Earth.

Over 99% of the impacts stay unnoticed
and damage is minimal.

But on rare occasions,
asteroids can be devastating.

13,000 years ago.

The great ice sheets were in retreat as
the last Ice Age was coming to an end.

The Clovis people, one of the first
human inhabitants of North America,

roamed the great plains
alongside giant beasts.

(TRUMPETS)

A team of archaeologists
is investigating the evidence they left

in the Sheriden Cave in Ohio,
southwest of Lake Erie.

Clovis peoples
were hunter-gatherers.

In other words, they hunted wild game
and they gathered wild plant foods.

At this time period,

there were animals
we call the mega-mammals,

which included large
elephant-like creatures

such as the woolly mammoth,
as well as the American mastodon.

Then, suddenly, all evidence
of the mega-mammals

and the weapons used by
the Clovis people disappeared.

The same observation
was made by geologists

at other excavation sites
across America.

Tankersley is convinced a catastrophe
drove the mammoths to extinction.

And it would have happened
in a snap of a finger,

over 30 genera of mega-mammals
went extinct

and the Clovis technology
disappeared forever.

Clues to what happened came
from another part of the cave.

It's in a geological formation
known as the Black Mat layer.

It is a dark line of rock
packed with charred debris,

and it suggests a violent death.

The black layer which you see
in this profile is carbon,

a high organic content, and what
we're seeing is the remains of animals

which were living at that time,

which, literally, had
the flesh burned off their bones.

In order to do that,
we're talking about somewhere

between 500
and 1,200 degrees Fahrenheit.

The cause of the inferno
has long been a mystery,

but, deep in these Ohio caves,
Tankersley thinks he has found traces

for an asteroid impact.

This is what's known
a magnetic susceptibility meter.

It looks at the degree of magnetism
of the layers of the sediments.

If we take a reading, in the layer that
predates the asteroid or comet strike,

and we look at the reading,
it's somewhere around seven.

If we compare that at the Black Mat,
where we're finding micro-meteorites,

we're looking at 50 times
the magnetism of the layer before,

we have evidence of an asteroid
or a large comet.

Like at Meteor Crater in Arizona,

Tankersley believes the asteroid
brought in large amounts of iron,

causing a strong magnetic field.

As the asteroid entered the atmosphere,

it burst into thousands
of smaller micro-meteorites.

He believes that the impact
annihilated the mega-mammals

and brought the Clovis people
to the edge of extinction.

Sceptics within the scientific community
doubt the theory.

They think the devastation could
have been caused by lightning,

or a wildfire started by the
Clovis people themselves.

But recently, further evidence
for the destructive power

of these killer rocks
has been uncovered.

In March 1994, Carolyn Shoemaker
and a team of astronomers

made an extraordinary discovery.

They were observing
and recording the night sky

when a giant fireball approached Jupiter.

Here was this
fuzzy bar of light,

and I looked at it
and thought, "What on Earth?

"It looks like a squashed comet,"

because it was fuzzy.

It wasn't quite an asteroid,
but a comet with a tail.

Now called Shoemaker-Levy 9,

the comet's mixture
of giant space rocks and ice

was heading directly for planet Jupiter.

Very exciting.

We had already been up on a high,

and we went up even farther,
because this was so unusual.

No-one had ever seen, actually seen,
a comet in orbit about Jupiter,

although we knew they had been there,

no-one had seen a comet
impact another body in space.

For the first time, the whole world
was watching rogue pieces of rock

hurtling through space towards a planet.

As they entered Jupiter's atmosphere,
something incredible happened.

The rogue pieces exploded,
causing giant shockwaves.

They left a series of holes in Jupiter,
each bigger than the Earth itself.

SHOEMAKER: The impact on Jupiter
was sensational, it was very large.

You could see the dark spot, and,
you know, you could see the first ring

and then you could see
this cloud of dust.

The team had witnessed an air burst.

As the giant fireballs
approached Jupiter at high speed,

they were slowed down
by the planet's atmosphere.

The energy of motion was converted
into pressure and heat

and resulted in a huge explosion.

A similar air burst over Earth
would annihilate all life on the planet.

Physicist Mark Boslough works

at the top secret Sandia Research
laboratories in New Mexico.

He's one of many defence scientists

investigating the possibilities
of such an Armageddon.

Research suggests we might not be
as safe as once thought.

The investigation leads
to a remote region of Siberia.

On June 30th, 1908, a bright
flash streaked through the skies.

Seconds later, the sound
of an explosion followed.

The area of Tunguska
was hit by an air burst.

A devastating shockwave
uprooted thousands of trees

and flattened more than
830 square miles of Taiga forest.

There is still some evidence,
um, there are some of these trees

that had all their branches
stripped off in 1908,

and those trees that have been
dead now for a hundred years

are still standing.

Scientists assumed the destruction
must have been caused by an asteroid

of at least 100 feet.

And they also believed asteroids
of this size would hit Earth

only once every thousand years.

But, in 2008, Boslough
discovered something alarming.

With advanced computer simulation,

he calculated that a small meteorite
of only 20 feet across

could cause a Tunguska-like event.

The... the air burst was actually smaller
than people have been thinking

for the last, um, 20 years or so.

And the reason we think it was smaller
was because of this neglect

of the momentum that continued
to carry the energy down.

What I'm showing here is an asteroid
coming from the upper right,

and it's pushing down
into the atmosphere,

and, about seven and a half miles
above the surface, it explodes.

But you can see that
it continues to push downwards,

so all that energy
is continuing to push downwards,

and it's driving this shockwave
ahead of it.

The shockwave is a big blast of air,
hurricane-force winds.

Now, that's what blows
the trees down.

Based on this theory, asteroids
able to cause another Tunguska

could statistically hit our planet
every hundred years.

If such an air burst happened
over a populated area,

the consequences would be devastating.

Well, if something like this were to hit
or explode over the sky of Los Angeles,

it would destroy buildings
over that same kind of area,

800 square miles or so,
so it could completely wipe out

a large portion of
the Los Angeles metropolitan area.

The investigation has revealed
that asteroid strikes

can be incredibly destructive.

The Black Mat layer of sediment
in the Sheriden Cave in Ohio

is evidence that an asteroid impact

might have led to the extinction
of the mega-mammals.

An explosion of a giant fireball
in Jupiter's atmosphere

showed scientists, in real time,
the destructive power of air bursts.

And an air burst over Siberia
leads to evidence

that a meteorite as small as 20 feet
across can cause massive devastation.

The powerful force of an asteroid is
evident, but the story doesn't end here.

The actual asteroid rocks,
when examined,

reveal extraordinary secrets about
the beginnings of our solar system.

Asteroids plunging from space have
transformed the surface of our planet.

But there was one thing
scientists still had to investigate.

The leftover pieces
of the asteroid rocks themselves.

They contain valuable information
about the origins of our solar system

and the formation of planet Earth.

But this presents geologists
with a problem.

Most giant asteroids vapourise
when they impact Earth,

destroying much of
their hidden evidence.

Geologists had to search for
smaller pieces of broken asteroids,

called meteorites, instead.

(OSCILLATING TONE)

With little weight,
these rocks survive the fiery plunge

through the Earth's atmosphere,
and land intact on the planet's surface.

(CRACKLING AND BLEEPING)

Geoff Notkin and his group
are hunting meteorites

in a dried-up riverbed in Arizona.

They are scanning the ground
with metal detectors,

hoping the signals they are getting
lead them to iron meteorites.

For the most part, they find iron dust,
small magnetic particles from space,

which stick to the magnetic hammer.

The estimate is thousands of tons of
meteorites fall on the Earth every year,

but most of those, the vast majority,
are tiny dust-sized particles

that collect over the surface of the Earth
and are never noticed.

What Notkin is really seeking
is not space dust

but extremely valuable pieces
of rock from outer space.

He has been hunting meteorites
for over 15 years

and has built up a collection
of over several hundred samples.

There are three basic types
of meteorites.

The irons, which are my favourite,

which are what most people imagine
a meteorite really looks like,

and they frequently have very attractive
aesthetic surface features

like this piece, caused by
melting in the atmosphere.

The next group are stones,

and these are fairly similar to... at least,
in appearance,

to terrestrial rocks,

although they contain chondrules
and iron and nickel from outer space,

which we don't find in Earth rocks.

And the third group, the stony irons,
is the rarest of the three,

and also the most valuable.

Um, the value on something like this
would be at least 25 to 30,000 dollars.

And if we were to take this piece
and cut it open,

we would reveal this beautiful
interior, olivine crystals,

and they're known popularly as
the semi-precious gemstone peridot.

Monetary value aside,
to geologists like Minnie Wadhwa,

these meteorites are a window
into the Earth's ancient past.

At Arizona State University,
she runs a department analysing

some of the oldest meteorite rocks
that landed on Earth.

This meteorite right here,

this carbon-rich chondrite, uh,

this probably is a close proxy
of the kinds of materials

that were bombarding the early Earth,
and they're called chondrites

because they've got these tiny little
inclusions, spherical inclusions in them

called chondrules, which are amongst,
uh, some of the earliest solids

that formed in our solar system.

In the beginnings of our solar system,
there was nothing but gas and dust.

As it cooled, solid asteroid rocks
began to form.

With modern technology, scientists have
been able to pinpoint their exact age.

Most meteorites are thought
to have formed 4.6 billion years ago,

but, um, modern techniques
have now made it possible for us

to actually age-date meteorites
with much greater precision,

and we now know, by looking at
meteorites like this one, for example, uh,

that, in fact, the solar system
was formed 4.567 billion years ago.

And we know that date, uh,
within a million years or so.

So, essentially, we can very precisely
age-date the formation

of our solar system
by looking at meteorites.

As the meteorite rocks
floated in early space,

they collided and grew
into bigger bodies.

These ancient rocks were the building
blocks of planets, including early Earth.

By looking at these types
of meteorites,

we can actually begin to understand
how our own Earth might have formed,

and, uh, what kinds of processes
might have happened on the early Earth,

because we actually get to look at, uh,
the deep interiors

of small planetary bodies

when we're actually looking
at some of these meteorites.

After the planets formed,
the rubble which was left accumulated

and formed a cloud of dust and rock
between Mars and Jupiter.

This is called the asteroid belt.

Every now and then,
one of these rocks breaks free

and tumbles through space
at 25,000 miles an hour.

When it drops through
the atmosphere and lands,

it delivers priceless information
about conditions on the early Earth.

Perhaps even hints
as to how life itself began.

In the late 1960s,
a remarkable fall of meteorites

hit the town of Murchison in Australia.

Scientists around the world took notice.

Well, basically, it consists
of silicate minerals, about...

Hundreds of pieces fell from space,
greeting the residents of Murchison

with a pungent smell
of rotting organic material.

If you open up this... this jar
of... of closed Murchison and smell it,

it actually smells, uh, very strongly of
sort of volatile organic-rich compounds

that are being de-gassed from
this particular rock even today.

Professor Wadhwa and her department

began analysing
the Murchison Meteorite.

Incredibly, they found it contained
organic compounds called amino acids.

These complex molecules
are essential to all life.

The organic materials
in this type of meteorite,

uh, were actually the building blocks
of... of life as we know it today.

This is the raw material from which,
uh, life began on our own planet.

It's possible that the seeds
of life arrived from space,

flown in by asteroids and meteorites.

In the case
of our own origins,

it's not absolutely clear that we need
of necessarily originated on Earth.

The seeds of our life
and the very primitive life forms

could have actually come
from another planet

or even another solar system.

New insights into asteroid impacts
has revolutionised our understanding

of how the Earth was made.

Overturned rock beds around Meteor
Crater were clues for a massive impact.

Advanced computer modelling

shows how asteroid rocks
are vapourised after impact.

Traces of iridium in the rocks in Sudbury
were evidence for an asteroid impact

that concentrated precious metals.

From meteorites landing on Earth,
scientists were able to calculate

that our solar system formed
exactly 4.567 billion years ago.

And the analysis of these space rocks
showed that the organic seeds of life

had perhaps arrived on Earth,
flown in from space.

Asteroid impacts
profoundly shaped

the geology
of our Earth.

But as examples

from the past
have shown,

they have the power

to annihilate our entire planet
in an instant.