>> Earth. A 4.5-billion-year-
old planet, still evolving.
As continents shift and clash,
volcanoes erupt, glaciers grow
and recede, the Earth's crust
is carved in numerous and
fascinating ways, leaving a
trail of geological mysteries
behind. In this episode,
investigators are exploring
the driest place on Earth--
the Atacama Desert in Chile.
This barren landscape is 50
times drier than Death Valley.
Now scientists are piecing
together the puzzle of how
this desert was made.
From raging volcanoes to
colossal mountains, oceans,
the clues they uncover also
provide a window into the
formation of the Earth itself.
S01x06 Driest Place on Earth Original Air Date on March 17, 2009
== sync, corrected by elderman ==
Earth is a blue planet,
engulfed by water. But in this
desolate chunk of Northern
Chile, you won't find a single
drop. Wedged between the
Pacific Ocean and coastal
volcanoes to the west, and the
Andes to the east, is Atacama,
the driest desert in the
world.
600 miles long, and narrow--on
average just 100 miles wide--
it's the same size as Iowa.
Now scientists are on a mission
to find out how it was made.
The investigation begins in
the sleepy town of Quillagua.
A rare green oasis, its only
lifeline is a stream trickling
300 miles from the Andes to
the Pacific.
It is home to the official
government rain gauge, so
geologist John Houston has
come here to find out how dry
the driest place on Earth
really is.
>> This is a pluviometer. It
measures the rainfall, uh,
every day.
>> Ah, ok.
>> For Marisa Vera, a government
scientist, it's a job with few
surprises.
>> How much rainfall has this
instrument recorded?
>> In the last 15 years, less
than one millimeter per year.
>> Less than one millimeter
a year?
>> Yes.
>> But was it every year?
>> It rains only three years.
>> That's incredible.
>> Exactly.
>> So less than one millimeter
a year.
>> On average, it rains three
one-hundredths of an inch a
year.
It would take a century for
Atacama's rainfall to fill a
coffee cup. How does this
compare with other deserts?
>> Here we have a cylinder,
and I'm going to show you the
difference between the amount
of rainfall per annum here and
the amount of rainfall in
other deserts. So if I fill
this jar up, right up to about
there, that is roughly the
rainfall that you get in the
Sahara. Now if I pour most of
that away, we get to that
level, that represents what we
have in the Mojave Desert,
five inches per annum. If I
pour all that away, except for
that little drop in the bottom
there, and that's the
equivalent of what we have
here in the heart of the
Atacama Desert. That is such a
small amount of rainfall that
it means it's the driest place
on Earth.
>> In his quest to find out
why Atacama gets so little
rainfall, Houston leaves the
oasis behind and heads into
the desert.
By the side of the
Pan-American Highway, a road
which runs the length of the
continent, he discovers the
first clue.
>> Well, here we are at the
Tropic of Capricorn. This is
one of the most important
latitudes in the world and
it is absolutely critical in
explaining why the Atacama
desert is in this location
here.
>> Most of the world's deserts
straddle one of two special
latitudes.
In the Southern Hemisphere,
the Tropic of Capricorn runs
through Atacama and Africa's
Namib and Kalahari deserts.
In the north, the Tropic of
Cancer runs right through the
vast Sahara. At these
particular positions on the
planet, the air is extremely
dry.
>> This instrument is called a
whirling hygrometer. What this
does is to measure the
relative humidity of the air.
And the reading on here gives
us a relative humidity of ten
per cent. That's really low,
really low. Um, there aren't
many places in the world where
you'd get a relative humidity
as low as that.
>> Back in the early 1700s,
scientists discovered why
tropical air is so dry.
European ships sailing to
America relied upon the trade
winds to power their
crossings, but English
meteorologist George Hadley
was mystified why they blew
westward when they should blow
directly north.
His studies would lead
scientists to understand how
air circulates around the
Earth.
At the equator, moisture-rich
air gets heated by the sun and
rises. As this hot, wet air
flows away from the Equator,
it quickly sheds its water as
rain. By the time it reaches
the two tropic latitudes, the
air has lost nearly all of its
moisture, resulting in no rain
on the land below.
The mystery, though, is why
Atacama gets so much less rain
than anyplace else.
Scientists hope to crack the
case by figuring out how
Atacama first formed.
On the hunt for clues, Houston
travels deep into the true
desert. This closely guarded
location was discovered during
routine mapping by geologists
back in the '70s, but the huge
significance of their find
wasn't realized until 1998.
This band of boulders is the
single most important clue to
Atacama's beginnings.
It's a delicate rock called
gypsum.
A simple test shows how
fragile it is.
>> If I pour a little bit of
water on top of that, you will
see that it very rapidly falls
apart. What's happening here,
of course, is that when I'm
putting water on this you see
it dissolve, I mean, it's just
going to fall apart.
>> The survival of gypsum as a
solid rock tells scientists
there hasn't been any heavy
rain since the rock formed.
So the next step was to date
it and figure out when this
place became dry.
Gypsum can't be directly
dated, but, by analyzing
fossils in the surrounding
rocks, the awesome age of the
desert was revealed.
Atacama is a staggering 150
million years old.
>> This gypsum here is an
extremely special gypsum.
If there had been any rainfall
greater than two inches in any
one year, this would have
dissolved and have been washed
away. What that means is
essentially that the Atacama
desert is the oldest desert in
the world.
>> For more than 150 million
years, while dinosaurs thrived
and became extinct, the
Himalayas formed and humans
evolved, Atacama has been a
desert. Gypsum also holds the
key to how this desert was
made. It's a chalky mineral
which forms not in deserts,
but in water. Gypsum exists in
a dissolved state in shallow,
warm, tropical seas. As the
water is evaporated away
by heat, it solidifies.
The existence of this one
little rock is a key piece of
evidence which reveals that
before Atacama became a
desert...
...it was a sea bed.
>> This really
insignificant-looking piece of
rock indicates that all this
desert was once underwater.
So this gypsum in this
location in the Atacama Desert
is absolutely critical to
understanding the whole
history of the Atacama Desert.
>> In the investigation so
far, scientists have pieced
together evidence of how and
when the desert first formed.
Atacama's location near the
Tropic of Capricorn means air
is dry and no rain falls.
Fossils found in the
surrounding gypsum rock
reveal the age of the desert.
Gypsum, a rock that forms only
in water, reveals Atacama was
once underwater.
Now, as scientists explore the
mystery of how Atacama evolved
from ocean floor to pure
desert, they unearth explosive
evidence in the investigation
of how the driest place on
Earth was made.
150 million years ago, the
Atacama Desert was a sea bed,
covered by ocean waters. But
today, some areas in the
desert are two miles above sea
level.
In the journey to find out how
this happened, scientists take
the investigation to the
eastern edge of the desert.
This strange landscape is the
largest geyser field in the
Southern Hemisphere.
>> We're up at the El Tatio
geyser field. You can see
around us that there's plenty
of hot springs and geysers,
there's plenty of steam around
and this is 'cause the air is
cool and the water is hot, and
so you have a lot of steam
and bubbling springs.
>> The boiling water is being
heated deep underground.
>> The geysers and the hot
water that you find up at El
Tatio are indications that you
have a body of hot rock
underneath us and another
indication is that you have a
bunch of volcanoes surrounding
this basin.
>> The Earth here is violently
alive.
Molten rock erupts onto the
surface, forming volcanoes.
The fiery volcanoes and the
boiling geysers are evidence
of a turbulent process
happening deep beneath the
desert.
Here, the Pacific Ocean crust
is being forced underneath
South America, much like a
spatula going underneath a
pizza. This geological process
is called subduction.
>> You have the Pacific plate
colliding with the continental
crust and the Pacific plate is
actually heavier and it slides
underneath the continental
crust. And as it does so, it
heats because it gets to a
depth of about 60 miles, and
it becomes molten.
>> This crucial depth is
called a melting zone. Hot
molten rock then thrusts
upward to form the active
volcanoes that ring the El
Tatio geyser field.
This process gives scientists
a hint to what lifted the
desert out of the ocean.
More clues are found on the
opposite side of the desert.
Geologists know that these
coastal hills were also once
volcanoes. Today, they're
completely dead, but modern
dating techniques show that
they first erupted over 195
million years ago. It's a
crucial piece of evidence
which reveals when the Pacific
plate first began to force its
way beneath South America.
At that time the desert,
indeed all of Chile, was
underwater. Over time, the
melting zone was pushed
further and further inland,
first igniting the coastal
volcanoes.
As the melting zone passed
beneath the desert, it formed
new crust, thickening and
raising the land. The Atacama
Desert slowly emerged.
50 million years ago, this
same process began to raise
the Andes.
Today, the melting zone is 140
miles inland and the molten
rock it produces ignites
volcanoes...
...and fuels El Tatio's
geysers.
But, as it passed under the
Atacama Desert, it also left
behind this.
Chuquicamata, the largest
open-pit copper mine in the
world.
Volcanic processes concentrated
the copper ore here, but it was
the desert's unique climate
that locked it in place.
>> This area of Northern Chile
produces some of the largest
and most important copper
deposits in the world. And
this is largely due to the
very dry climate.
Most of the erosion on the
Earth's surface is caused by
water. So here. Where there's
so little rainfall, and
there's very little surface
water, there's not very much
erosion and so the copper
deposit has actually
remained intact.
>> As a result, this barren
wilderness is one of the most
valuable pieces of land on the
planet.
The mystery of how a desert
can rise from the sea can be
solved.
Geysers provide evidence that
molten rock exists deep
underground. The existence of
active volcanoes shows the
movement of one continental
plate under another. Extinct
volcanoes show this process
began at the coast and
pushed inland, raising the
desert above the ocean.
The next step is to try and
figure out what turned this
ancient sea floor into the
driest place on Earth. A quest
that spans 200 years of
history and solves the riddle
of what brought these penguins
to the edge of the desert.
The Atacama Desert is
intriguing because it is the
driest place on Earth.
Deserts by their very nature
are dry, but Atacama is
unique. It's 50 times drier
than Death Valley in
California. And it's not
because it's hotter. Atacama
averages around 80 degrees
Fahrenheit during the day,
whereas temperatures in Death
Valley regularly soar above
110.
The search for what turned
this strip of land from a
regular desert into the
world's driest place begins
out on the open sea.
>> One of the curious things
about the Atacama is that we
actually see here penguins.
Penguins obviously like cold
water and that's really
confusing when you think of
on shore we have really hot
conditions. In fact, the
temperature of the water here
is about 55 degrees
Fahrenheit, whereas on land
the temperature is something
like 80 degrees Fahrenheit.
>> These penguins were first
described by explorer
Alexander Von Humboldt, over
200 years ago. While traveling
along this coast, he was
puzzled by the huge variety of
marine life. Measuring the
temperature of the water gave
him an explanation. It was 20
degrees colder than expected--
perfect for sea life like
penguins.
Centuries later,
meteorologists began to wonder
if this chilly belt of water,
called the Humboldt Current
after the explorer, was the
reason Atacama became the
driest place on Earth.
>> The Humboldt Current comes
all the way up from
Antarctica, bringing with it
cold water, and it is this
cold water which creates this
dull grey day that we see
here, with a fog overlying us.
>> It causes the air above it
to cool, forming a thick bank
of cold cloud and fog which
clings to the shore. Hot, dry
air descends at the tropics.
Here, that hot air sits on top
of the cold, heavy rainclouds,
holding them down.
Meteorologists call this an
inversion layer. Trapped at
3,000 feet, the clouds can't
rise up and shed their rain on
the high-altitude desert.
>> The inversion layer
prevents any moisture that may
accumulate close to the sea
from moving inland. So that is
one of the reasons why this
Humboldt Current actually
contributes to the dryness of
the Atacama Desert that we see
just over there.
>> But is it this inversion
layer, created by the
Humboldt Current, that has
turned Atacama into the
driest desert in the world?
In the desert's northern tip,
in a desolate place called
Quebrada Aroma, geologist
Laura Evenstar is looking for
clues to solve this riddle.
She's trying to put a date on
when the desert became so very
dry.
Other deserts, like the
Mojave, don't get much rain,
but when they do, it's
dramatic. Storms bring heavy
rains and flash floods.
But not here in the Quebrada
Aroma, which is now totally
dry. One way to date the last
time there would have been
enough rainfall to cause a
flash flood is to try to find
out how long the rocks have
been lying there undisturbed.
>> What we have here is a
miniature demonstration of
what goes on if you start
having large amounts of
rainfall. So, this is our
rainfall here...
...and what we can see is that
when we start raining on our
desert surface,
it'll pick up the boulders and
move them around and then when
there's no water here, the
boulders just sit still and
don't move.
>> The surface of Quebrada
Aroma is strewn with rocks, so
she's cracking them open to
reveal evidence of exactly
when water last flooded the
landscape.
>> What we do is we have to
knock a bit off, and then we
examine it and have a look at
whether it's got a--a very
dark color, and hopefully we
can be able to see some of the
black minerals, which is what
we're looking for.
>> The tiny black crystalline
minerals are pyroxenes.
They're crucial evidence
because, like microscopic
geologic clocks, their
chemistry changes when
exposed to cosmic radiation
over time.
>> The sun is only producing a
tiny bit of the radiation
which will hit this rock, the
majority of it is coming from
all the stars you see in the
night sky. What it does to the
rock is basically, uh, just
bakes it, a bit like a really
bad suntan, so it just comes
down, hits it and cooks it.
>> As the rock gets cooked by
cosmic rays, the pyroxenes
break down and produce a gas
called helium-3.
>> We can record how much
helium-3 is within this rock,
and the more we have, the
longer that it has been
exposed to cosmic or, uh,
solar radiation.
>> Helium-3 gas is only
produced in microscopic
quantities, so Evenstar takes
her samples to a lab 7,000
miles away in Glasgow,
Scotland.
>> So what we do, uh, using a
laser, is we shoot the laser
into one of the wells, and
vaporize our crystals.
And that's releasing the
helium-3, then the helium-3 is
going to go through all this
complicated machinery,
eventually run through the
mass spectrometer.
>> By analyzing this data, she
can figure out the last time
the boulders were moved.
>> The oldest age sample we've
actually recorded has been 23
million years. So what this
means is that, within certain
areas of the Atacama Desert,
these boulders have been
sitting there and not moved by
water for 23 million years.
So the Atacama Desert is one of
the oldest undisturbed
surfaces in the world. These
boulders were there before
humans even started to exist,
they are incredibly old.
>> Evenstar has discovered that
there are places in the desert
which have been bone dry for
23 million years.
This date is a crucial clue in
the investigation, because it
coincides with the birth of
the Humboldt Current. South
America was once joined to
Antarctica. But, roughly 25
million years ago, these
continents split. A channel
opened. Freezing water began
to circulate round the pole,
and thundered north along the
coast.
This cold current
formed an inversion layer,
trapping coastal rainclouds
and starting Atacama's slow
transformation into the driest
place in the world.
But the Humboldt Current is
not the only culprit.
Ironically, the quest to find
out how the desert became so
dry comes up against one of
the wettest places on Earth.
On the other side of Atacama
is the Amazon, but the heavy
rainfall from the rainforest
doesn't get anywhere near the
desert. The reason why is in
plain sight. Between the
Amazon and the Atacama Desert
lies the vast Andes Mountain
range. Geologic evidence
suggests the Andes finally
grew high enough, some ten
million years ago, to prevent
any rain from reaching the
desert. It's called a
rainshadow effect, and it's
the final factor which drove
Atacama to become the driest
place on Earth.
The evidence for what turned
Atacama so incredibly dry is
mounting. The Humboldt Current
creates a weather system that
allows no rainfall. Helium-3
in rocks shows that the
process of desiccation
began 23 million years ago.
The rising Andes, ten million
years ago, made it drier
still. The investigation would
seem to be conclusive.
Atacama has been a barren,
essentially rainless landscape
for millions of years.
But then something happened to
blow that conclusion wide
open. Tiny shards of stone
revealed that an ancient
civilization once lived here.
But how could people live in
the world's driest desert?
The Atacama Desert is by far
the driest place on Earth, and
by piecing together the
evidence, scientists believed
it had been so for millions of
years.
Yet, at a remote site called
Guanaqueros, paleoecologist
Claudio LaTorre made an
intriguing discovery which
paints a more complex picture.
>> This is, uh, an
extraordinary find, and this
was probably a little knife or
a scraper that's been broken
off and discarded. That could
probably still cut.
>> To the untrained eye, it
looks like a simple rock
shard, but LaTorre can see
it's been worked into a tool.
And he's found hundreds of
them. They're clues that
reveal ancient humans once
lived here.
>> This was not just a
temporary residence, this was
something where people were
living and working and banging
away at rocks and making
artifacts and living off this
landscape, using the resources
at hand.
>> As water is essential for
life, it seems impossible that
any kind of plant, animal or
human life could survive here.
LaTorre suspects that some
regions of this 57,000-square-
mile desert were once much
wetter. Not millions of years
ago, but during the time
humans walked the Earth.
In 1997, he set off on a
mission to hunt for evidence.
Today, he's retracing that
journey. Changes in the
climate can be seen in the
rocks, so LaTorre examines the
cliff layer by layer. He finds
a crucial piece of evidence.
>> This is actually where the
interesting part of the story
comes in.
>> This chalky rock is called
diatomite.
It's made from the crushed
remains of fossilized algae,
microscopic life forms which
only live in freshwater.
>> What this rock is telling us
is that we had basically a
wetland.
Whereas you look at the
landscape across today and we
see that it's basically about
as dry as you can get.
>> Sometime in the past there
was water on the surface of
the desert. Latorre's next
task was to find out when.
Radiocarbon dating is one of
the most accurate methods of
dating, but using this method
means sampling something
organic. So LaTorre combed the
desert for clues.
>> The way we work
is basically poking our heads
into every little hole and
crevice that we can find.
When we found this place, we
couldn't believe our eyes.
>> He accidentally and luckily
stumbled upon the most
important piece of evidence in
this investigation. At the
back of the cave was a vast
nest. It's made from the feces
of thousands of generations of
tiny mammals. The size and
shape of the pellets told
LaTorre those animals were
Chinchilla rats.
And it also contained the
critical clue he was searching
for--
organic material.
>> When we found this site,
one of the most exciting
discoveries that we made was
the fact that it's full of
grasses. Now, look across the
landscape today and tell me
where those grasses are, and
we immediately knew that we
were talking about some major
vegetation change.
>> This grass looks as fresh
and crisp as if it was
collected yesterday. But when
LaTorre carbon-dated grass
from the nest, what he found
was amazing. The grass was
more than 11,000 years old.
>> What I have in my hands
here is an ancient ecosystem.
This is about as clear an
indicator you can get, better
than anything else you can
think of, that water increased
in the past in this area.
>> The nest reveals strong
evidence that plants and
mammals did exist here, and
they weren't alone.
Underneath the thick layer of
nest is another layer, rich
with tiny handmade tools.
>> If we look around, you
know, we can find actually
evidence of this past human
occupation, there's just--full
of little shards here on the
floor.
>> Some regions of Atacama
have been constantly dry for
23 million years. But this
evidence shows that other
regions, like Guanaqueros,
were very different 11,000
years ago.
It's a fossilized snapshot of
a diverse ecosystem briefly
bursting into life. Grasses
grow and wetlands flourish in
this wetter time. Tiny mammals
thrive and breed, while game
like vicuña and llamas meant
humans could live in this rich
and fertile environment.
>> So it's wonderful to know
that, by looking at something
as mundane as, uh, a rodent
nest, you can actually find
clues that enable you to
understand the past human
colonization of the Atacama
Desert, which is no mean feat
in itself, given the fact that
it's such a harsh climate today.
>> The date of the rat's nest
gives scientists a possible
theory of where the water came
from.
11,000 years ago, the last Ice
Age was at an end.
The global climate was changing.
More rain fell high in the
Andes, flowing down to the
desert in rivers.
In some places, groundwater
pooled, forming wetlands.
Others remained untouched by
water, as they had for
millions of years.
But, just a thousand years
later, the climate changed
again. Rivers dried up.
Grasses died. Rats and humans
disappeared. Now, every drop
of groundwater has been sucked
down into the parched earth.
LaTorre demonstrates how deep
that water is today.
>> So, just to give you an
idea of how much change has
gone on since the wetland was
formerly at the surface,
here's a little experiment
that we can do. This is a
well, and I'll drop this
little rock, and we're going
to count and we're going to
see how long it takes for that
rock to hit the water.
So that takes almost four
seconds to reach the water,
that's well over 200 feet
below the surface is where the
water table is today. It's
about as dry as it gets. It's,
uh, it's what we call absolute
desert. No plants, no wildlife,
nothing, no surface running
water whatsoever.
>> The investigation of this
driest place on Earth took a
surprising turn. Tools show
humans lived here. Diatomite
reveals the climate was once
wetter. Rats' dung and grass
dates a diverse ecosystem to
11,000 years ago.
Yet this extraordinary desert
has more secrets to tell, not
just about life in one of the
most extreme environments on
our planet, but also about
life on other planets.
Today, scientists suspect
Atacama is the driest it has
ever been, so they're
investigating whether there's
any source of water left here
at all. And NASA scientist
Alfonso Davila knows that if
there's water, there's a
chance there could be life
here too. But when he first
arrived, the signs didn't look
good.
>> When I came here for the
first time. I drove for a
couple of thousand miles, and
when I got, uh, back to my
base camp, I realized that I
didn't have a single insect
smashed against my windshield.
That has never happened to me
anywhere else in the world and
I--and I think that's a very
good example of, uh, how hard
this environment is for life.
>> Since the 1960s, NASA
scientists have been hunting
for bacteria life in the
desert's thin soils, yet they
found nothing...
...until 2005, when they came
across a strange white
landscape.
By chance, one of Davila's
colleagues picked up a rock,
smashed it open and discovered
something completely
unexpected.
>> Yeah, you can see very
nicely a--a green layer inside
the crust.
>> Under the microscope, the
significance of this pale
green blur zoomed sharply into
focus.
>> To our surprise, we saw a
green microorganism living
inside the rock. So that came
as a big surprise, uh, because
nobody was expecting
microorganisms in the middle
of the driest place on Earth.
>> Completely by accident,
hidden inside a rock they'd
discovered life.
>> This mineral is, uh, sodium
chloride, otherwise known as
halite. It's a very common
mineral in the Atacama Desert
and it's also a very common
mineral in kitchens around the
world, as this is exactly the
same salt we use to spice our
food.
>> Salt can preserve food by
killing off bacteria. But
here, strangely, it was
harboring a colony of green
microbes. To find out how they
survive, Davila laid out a
series of sensors that measure
humidity. His research shows
that, although, on average,
the air in the desert is
around ten per cent humidity,
on rare occasions, it rises as
high as 75 per cent.
This momentary increase in
water vapor is the only
source of water.
And it's this water that gives
rise to life.
>> The distinctive property of
salt is its capability to
extract water vapor from the
atmosphere and forms a liquid
solution inside the rock.
>> As moisture from the air is
sucked into the salt, the
microbes allow the rock to
bring the water to them.
>> Life is actually very
robust, it's, uh, very
flexible and it can really
adapt to some of the most
extreme conditions that we see
on Earth.
>> NASA believes this
discovery in the Atacama
desert can reveal something
about life on Mars.
In 1976, the Viking Lander
detected water in Mars's thin
atmosphere.
In 2008, NASA's Mars Odyssey
Orbiter found evidence of salt
on the planet's surface.
Now, when humans finally get
to Mars, they won't be looking
for life in the thin Martian
soils, but inside the rocks.
>> Unfortunately, it's gonna
be a long time until we see
humans walking on Mars.
Until then, we come to the
Atacama Desert, uh, and we
study this type of rocks,
which likely hold the clue to
understanding life on Earth
and also to understanding the
potential for life in other
planets in our solar system.
>> So it's possible that an
accidental discovery in the
driest place on Earth will one
day lead scientists to crack
open a Martian rock and
discover little green alien
life.
The investigation into how the
driest place on Earth was made
has revealed an awesome Earth
story spanning 150 million
years.
Gypsum, a rock which forms in
water, shows the desert was
once a sea bed. Hot geysers
show that immense volcanic
activity under the desert
raised it above the ocean.
Tiny pyroxene crystals reveal
the first areas of the desert
which became completely dry 23
million years ago. Rat nests
reveal a small pocket of life
that bloomed in the desert at
the end of the last Ice Age.
Tiny green organisms in salt
show that even here, life
clings on.
Today this place is unique on
earth--absolute perfect desert,
and the investigation into how
it formed has shed light
on another chapter in the story
of how the Earth was made.
== sync, corrected by elderman ==