NARRATOR: 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. 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. [music playing] There is a giant hole in the
Arizona desert 35 miles east of Flagstaff. It's huge-- 3/4 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. NARRATOR: 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. DAVID KRING: 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. NARRATOR: 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 ground water, creating a steam explosion,
which causes a blast that produces craters like
the one over my shoulder. NARRATOR: 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
geologic terrain or created by any
terrestrial geologic process. NARRATOR: 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 size, he
calculated that the asteroid must have weighed
10 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. DAVID 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. NARRATOR: For years,
Barringer and his men found only small
fragments of iron. Undeterred by this, they
kept digging deeper shafts into the Earth. DAVID KRING: The largest
of which, the main shaft, you can see is a
white island of debris in the center of the crater. And 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. NARRATOR: 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. NARRATOR: To Barringer,
the pulverized rock was a major clue that
pointed to one thing-- the violent impact
of an asteroid. DAVID KRING: 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 I need to figure it out. NARRATOR: Barringer also
discovered other oddities. At the crater rim, he
noted a bit 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 upward. And if you look very closely
at the very top of the rim, they are completely overturned. NARRATOR: 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, $10
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. NARRATOR: Proof of
Barringer's asteroid theory would get a boost
some six decades later from an unexpected source [explosion] 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 certainly told him that
there was a strong similarity because they were so
obvious a meteor crater. NARRATOR: Shoemaker came upon
another important clue that linked the Nevada test
sites to Meteor Crater. He found samples of
this very unusual rock. This was once sandstone, but he
recognized it had been altered. NARRATOR: 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. NARRATOR: They were caused by
the incredible energy released in the shock waves
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. [explosion] 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
deposited on the landscape. Within seconds, the shockwave
and the very high velocity air blast radiate across
the landscape. NARRATOR: 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. DAVID KRING: 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. NARRATOR: 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. DAVID KRING: 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 Stone. 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. NARRATOR: 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 center 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. NARRATOR: 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
revealed new evidence. What we have is a conical-type
fracture system with these lineations or lines
running through them. And they focus
down into a point. NARRATOR: 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 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. NARRATOR: 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. JOHN SPRAY: 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. NARRATOR: 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 meteorites. NARRATOR: To find iridium, the
lab samples of the crushed rock are heated in a furnace to
over 1,000 degrees Celsius. The rock melts and
metals in the rock separate out and form a disk. When the disk cools, it is
analyzed for traces of iridium. Hi, Jim. How's it going? NARRATOR: 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 10 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 3/4 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 blows off. And you end up fragmenting the
projectile, the meteorites, 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. NARRATOR: 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. NARRATOR: 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. [music playing] 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
recognize signs of large impact sites. Shatter cones where evidence
of strong shock waves. 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. This has led scientists to
a terrifying conclusion. If it has happened in the
past, there is little doubt it could happen again. October 9, 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 20, 2008, an
asteroid struck Earth again. A mighty fireball streaked
over Western Canada. As it dash 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. [music playing] 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. [roaring] A team of archaeologists is
investigating the evidence they left in the Sheriden cave
in Ohio southwest of Lake Erie. KEN TANKERSLEY: 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. NARRATOR: 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. NARRATOR: 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. KEN TANKERSLEY: 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. NARRATOR: 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 as 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 7. If we compare that
at the black mat where we're finding
micrometeorites, we're looking at 50 times
the magnetism of the layer before we have evidence of
an asteroid or a large comet. NARRATOR: 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 micrometeorites. He believes that the impact
annihilated the mega mammals and 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. NARRATOR: 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. CAROLYN SHOEMAKER:
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. NARRATOR: 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. CAROLYN SHOEMAKER: The impact
on Jupiter was sensational. It was very large. You could see the dark spots. You could see the first
ring, and then you could see this cloud of dust. NARRATOR: 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 30, 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. There are some of these trees
that had all their branches stripped off in 1908. And those trees that have
been dead now for 100 years are still standing. NARRATOR: 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 air burst was
actually smaller than people have been thinking
for the last 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 7 and 1/2 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. NARRATOR: 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. NARRATOR: 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 evidence, but the story doesn't end here. The actual asteroid
rocks when examined reveal extraordinary
secrets about the beginnings of our solar system. [music playing] 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. NARRATOR: 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. And the value on
something like this would be at least
$25,000 to $30,000. 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 semiprecious gemstone peridot. NARRATOR: 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, 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 some of the
earliest solids that formed in our solar system. NARRATOR: 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 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, that, in fact,
the solar system was formed 4.567 billion years ago. And we know that date within
a million years or so. So essentially, we
can very precisely age date the formation
of our solar system by looking at meteorites. NARRATOR: 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. MINNIE WADHWA: By looking at
these types of meteorites, we can actually begin to
understand how our own Earth might have formed and
what kinds of processes might have happened
on the early Earth because we actually get to
look at the deep interiors of small planetary bodies when
we're actually looking at some of these meteorites. [music playing] NARRATOR: 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 silicon minerals. NARRATOR: Hundreds of
pieces fell from space, greeting the
residents of Murchison with the pungent smell of
rotting organic material. If you open up this jar of
closed Murchison and smell it, it actually smells
very strongly of sort of volatile organic
rich compounds that are being degassed from this
particular rock even today. NARRATOR: 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 were actually the
building blocks of life as we know it today. This is the raw
material from which life began on our own planet. NARRATOR: It's possible
that the seeds of life arrived from space flown in
by asteroids and meteorites. JOHN SPRAY: In the case
of our own origins, it's not absolutely clear
that we need have necessarily originated on Earth. The seeds of all life and
the very primitive life forms could have actually come
from another planet or even another solar system. NARRATOR: 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. [music playing]
