>> 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.
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 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 ==