Original subtitles

>> 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.

S01x10 Asteroids Original Air Date on April 21, 2009

== sync, corrected by elderman ==

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.

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 of 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.

When Gilbert arrived,

he realized 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, uh, 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 the

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 other 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 dollars 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.

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.

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, pulverized rock 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 pulverized

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 recognized 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 vaporized. Conclusive

evidence came in 1997 when

scientists were able to simulate

the impact using advanced

computer modeling. 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 traveled back

up through the asteroid's iron

core, vaporizing 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 modeling revealed that

the speed and size of the

asteroid created enough energy

for the rock to vaporize 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

recognized 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

revolutionize 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 analyze 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

analyzed 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 as 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 vaporized, 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 hit 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

recognize 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 traveled 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.

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 a

brought the Clovis people to the

edge of extinction.

Skeptics 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.

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 defense

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 a 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 vaporize when they

impact Earth, destroying much of

their hidden evidence.

Geologists had to search for

smaller pieces of broken

asteroids, called meteorites,

instead.

With little weight, these rocks

survive the fiery plunge

through the Earth's atmosphere,

and land intact on the planet's

surface.

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 favorite, 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 analyzing

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 analyzing 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 revolutionized our

understanding of how the Earth

was made.

Overturned rock beds around

Meteor Crater were clues for a

massive impact.

Advanced computer modeling shows

how asteroid rocks are

vaporized 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.

== sync, corrected by elderman ==