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

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

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the Earth's crust is carved
in numerous and fascinating ways,

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leaving a trail
of geological mysteries behind.

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In this episode, investigators are
exploring the driest place on Earth -

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the Atacama Desert in Chile.

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This barren landscape is 50 times drier
than Death Valley.

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Now scientists are piecing together
the puzzle of how this desert was made.

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From raging volcanoes to
colossal mountains, oceans,

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the clues they uncover
also provide a window

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into the formation of the Earth itself.

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Earth is a blue planet, engulfed by water.

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But in this desolate chunk of northern
Chile, you won't find a single drop.

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Wedged between the Pacific Ocean
and coastal volcanoes to the west,

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and the Andes to the east, is Atacama,
the driest desert in the world.

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600 miles long, and narrow -
on average just 100 miles wide -

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it's the same size as lowa.

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Now scientists are on a mission
to find out how it was made.

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The investigation begins
in the sleepy town of Quillagua.

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A rare green oasis,
its only lifeline is a stream

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trickling 300 miles
from the Andes to the Pacific.

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It is home to the official
government rain gauge,

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so geologist John Houston
has come here

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to find out how dry
the driest place on Earth really is.

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This is a pluviometer.
It measures the rainfall, uh, every day.

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Ah, OK.

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For Marisa Vera, a government scientist,
it's a job with few surprises.

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How much rainfall
has this instrument recorded?

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In the last 15 years,
less than one millimetre per year.

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Less than one millimetre a year?
Yes.

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But was it every year?

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It rains only three years.

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That's incredible.
Exactly.

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So less than one millimetre a year.

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On average, it rains three
one-hundredths of an inch a year.

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It would take a century for
Atacama's rainfall to fill a coffee cup.

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How does this compare
with other deserts?

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Here we have a cylinder,

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and I'm going to show you the
difference between the amount

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of rainfall per annum here and
the amount of rainfall in other deserts.

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So if I fill this jar up,
right up to about there,

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that is roughly the rainfall
that you get in the Sahara.

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Now if I pour most of that away,
we get to that level,

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that represents what we have
in the Mojave Desert,

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five inches per annum.

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If I pour all that away, except for
that little drop in the bottom there,

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and that's the equivalent
of what we have here

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in the heart of the Atacama Desert.

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That is such a small amount of rainfall

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that it means
it's the driest place on Earth.

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In his quest to find out
why Atacama gets so little rainfall,

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Houston leaves the oasis behind
and heads into the desert.

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By the side
of the Pan-American highway,

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a road which runs the length of the
continent, he discovers the first clue.

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Well, here we are
at the Tropic of Capricorn.

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This is one of the most important
latitudes in the world

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and it is absolutely critical in
explaining why the Atacama Desert

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is in this location here.

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Most of the world's deserts
straddle one of two special latitudes.

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In the southern hemisphere,

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the Tropic of Capricorn
runs through Atacama

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and Africa's Namib
and Kalahari Deserts.

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In the north, the Tropic of Cancer
runs right through the vast Sahara.

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At these particular positions
on the planet, the air is extremely dry.

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This instrument is called
a whirling hygrometer.

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What this does is to measure
the relative humidity of the air.

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And the reading on here gives us
a relative humidity of 10%.

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That's really low, really low.

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Um, there aren't many places in the
world where you'd get a relative humidity

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as low as that.

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Back in the early 1700s,

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scientists discovered
why tropical air is so dry.

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European ships sailing to America
relied upon the trade winds

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to power their crossings, but
English meteorologist George Hadley

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was mystified why they blew westward
when they should blow directly north.

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His studies would lead scientists
to understand how air circulates

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around the Earth.

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At the equator, moisture-rich air
gets heated by the sun and rises.

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As this hot, wet air flows away
from the equator,

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it quickly sheds its water as rain.

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By the time it reaches
the two tropic latitudes,

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the air has lost nearly all of its moisture,
resulting in no rain on the land below.

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The mystery, though,

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is why Atacama gets so much
less rain than anyplace else.

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Scientists hope to crack the case by
figuring out how Atacama first formed.

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On the hunt for clues, Houston
travels deep into the true desert.

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This closely guarded location was
discovered during routine mapping

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by geologists back in the '70s,

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but the huge significance of their find
wasn't realised until 1998.

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This band of boulders is the single most
important clue to Atacama's beginnings.

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It's a delicate rock called gypsum.

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A simple test shows how fragile it is.

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If I pour a little bit of water on top of that,
you will see that it very rapidly falls apart.

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What's happening here, of course,

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is that when I'm putting water on this,
you see it dissolve,

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I mean, it's just going to fall apart.

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The survival of gypsum as a solid rock

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tells scientists there hasn't been
any heavy rain since the rock formed.

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So the next step was to date it and
figure out when this place became dry.

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Gypsum can't be directly dated,

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but by analysing fossils
in the surrounding rocks,

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the awesome age
of the desert was revealed.

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Atacama is a staggering
150 million years old.

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This gypsum here is an
extremely special gypsum.

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If there had been any rainfall greater
than two inches in any one year,

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this would have dissolved
and have been washed away.

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What that means is essentially

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that the Atacama Desert
is the oldest desert in the world.

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For more than 150 million years, while
dinosaurs thrived and became extinct,

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the Himalayas formed and humans
evolved, Atacama has been a desert.

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Gypsum also holds the key
to how this desert was made.

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It's a chalky mineral
which forms not in deserts, but in water.

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Gypsum exists in a dissolved state
in shallow, warm, tropical seas.

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As the water is evaporated away
by heat, it solidifies.

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The existence of this one little rock
is a key piece of evidence

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which reveals that before Atacama
became a desert...

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...it was a sea bed.

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This really insignificant-looking
piece of rock indicates

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that all this desert
was once underwater.

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So this gypsum in this location
in the Atacama Desert

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is absolutely critical to understanding
the whole history of the Atacama Desert.

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In the investigation so far, scientists
have pieced together evidence

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of how and when the desert first formed.

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Atacama's location near
the Tropic of Capricorn means air

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is dry and no rain falls.

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Fossils found in the
surrounding gypsum rock

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reveal the age of the desert.

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Gypsum, a rock that forms only in water,
reveals Atacama was once underwater.

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Now, as scientists explore the mystery
of how Atacama evolved

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from ocean floor to pure desert,

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they unearth explosive evidence
in the investigation

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of how the driest place on Earth
was made.

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150 million years ago,
the Atacama Desert was a sea bed,

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covered by ocean waters.

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But today, some areas in the desert
are two miles above sea level.

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In the journey to find out
how this happened,

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scientists take the investigation
to the eastern edge of the desert.

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This strange landscape is the largest
geyser field in the southern hemisphere.

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We're up at
the El Tatio geyser field.

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You can see around us that there's
plenty of hot springs and geysers,

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there's plenty of steam around

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and this is 'cause the air is cool
and the water is hot,

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and so you have a lot of steam
and bubbling springs.

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The boiling water is being heated
deep underground.

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The geysers and the hot water
that you find up at El Tatio

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are indications that you have a body
of hot rock underneath us

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and another indication is that
you have a bunch of volcanoes

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surrounding this basin.

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The Earth here is violently alive.

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Molten rock erupts onto the surface,
forming volcanoes.

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The fiery volcanoes and the
boiling geysers are evidence

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of a turbulent process
happening deep beneath the desert.

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Here, the Pacific Ocean crust is being
forced underneath South America,

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much like a spatula
going underneath a pizza.

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This geological process
is called subduction.

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You have the Pacific Plate
colliding with the continental crust

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and the Pacific Plate is actually heavier

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and it slides
underneath the continental crust.

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And as it does so, it heats because
it gets to a depth of about 60 miles,

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and it becomes molten.

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This crucial depth
is called a melting zone.

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Hot molten rock then thrusts upward
to form the active volcanoes

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that ring the El Tatio geyser field.

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This process gives scientists a hint to
what lifted the desert out of the ocean.

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More clues are found on the
opposite side of the desert.

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Geologists know that these coastal hills
were also once volcanoes.

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Today, they're completely dead,
but modern dating techniques

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show that they first erupted
over 195 million years ago.

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It's a crucial piece of evidence
which reveals when the Pacific Plate

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first began to force its way
beneath South America.

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At that time the desert,
indeed all of Chile, was underwater.

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Over time, the melting zone was pushed
further and further inland,

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first igniting the coastal volcanoes.

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As the melting zone passed
beneath the desert, it formed new crust,

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thickening and raising the land.

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The Atacama Desert slowly emerged.

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50 million years ago, this same process
began to raise the Andes.

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Today, the melting zone
is 140 miles inland

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and the molten rock it produces
ignites volcanoes...

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...and fuels El Tatio's geysers.

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But, as it passed under the
Atacama Desert, it also left behind this.

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Chuquicamata, the largest
open-pit copper mine in the world.

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Volcanic processes
concentrated the copper ore here,

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but it was the desert's unique climate
that locked it in place.

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This area of northern Chile
produces some of the largest

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and most important copper
deposits in the world.

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And this is largely due
to the very dry climate.

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Most of the erosion on the
Earth's surface is caused by water.

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So here where there's so little rainfall,
and there's very little surface water,

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there's not very much erosion

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and so the copper deposit
has actually remained intact.

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As a result, this barren wilderness

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is one of the most valuable pieces
of land on the planet.

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The mystery of how a desert
can rise from the sea can be solved.

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00:17:32,814 --> 00:17:38,399
Geysers provide evidence that
molten rock exists deep underground.

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00:17:38,399 --> 00:17:42,984
The existence of active volcanoes
shows the movement

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00:17:42,984 --> 00:17:45,569
of one continental plate under another.

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00:17:46,570 --> 00:17:51,530
Extinct volcanoes show this process
began at the coast and pushed inland,

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00:17:51,530 --> 00:17:53,989
raising the desert above the ocean.

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00:17:55,364 --> 00:18:00,533
The next step is to try and figure out
what turned this ancient sea floor

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into the driest place on Earth.

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00:18:03,910 --> 00:18:08,411
A quest that spans 200 years
of history and solves the riddle

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00:18:08,411 --> 00:18:12,955
of what brought these penguins
to the edge of the desert.

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00:18:19,249 --> 00:18:25,418
The Atacama Desert is intriguing
because it is the driest place on Earth.

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00:18:25,418 --> 00:18:31,545
Deserts by their very nature
are dry, but Atacama is unique.

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It's 50 times drier than Death Valley
in California.

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00:18:36,713 --> 00:18:39,798
And it's not because it's hotter.

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Atacama averages around 80 degrees
Fahrenheit during the day,

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whereas temperatures in
Death Valley regularly soar above 110.

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The search for what turned this strip
of land from a regular desert

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00:18:58,055 --> 00:19:04,016
into the world's driest place
begins out on the open sea.

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00:19:06,809 --> 00:19:09,101
One of the curious things
about the Atacama

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00:19:09,101 --> 00:19:12,602
is that we actually see here penguins.

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00:19:12,602 --> 00:19:17,354
Penguins obviously like cold water
and that's really confusing

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00:19:17,354 --> 00:19:22,814
when you think of on shore
we have really hot conditions.

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00:19:22,814 --> 00:19:32,110
In fact, the temperature of the water
here is about 55 degrees Fahrenheit,

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00:19:32,110 --> 00:19:37,987
whereas on land the temperature is
something like 80 degrees Fahrenheit.

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00:19:41,280 --> 00:19:45,781
These penguins were first described
by explorer Alexander von Humboldt,

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00:19:45,781 --> 00:19:47,616
over 200 years ago.

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While travelling along this coast,

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00:19:50,951 --> 00:19:55,202
he was puzzled
by the huge variety of marine life.

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00:19:56,286 --> 00:19:59,412
Measuring the temperature of
the water gave him an explanation.

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00:20:01,372 --> 00:20:04,998
It was 20 degrees colder
than expected -

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00:20:04,998 --> 00:20:08,040
perfect for sea life like penguins.

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00:20:12,125 --> 00:20:17,961
Centuries later, meteorologists began
to wonder if this chilly belt of water,

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00:20:17,961 --> 00:20:21,254
called the Humboldt Current
after the explorer,

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was the reason Atacama became
the driest place on Earth.

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The Humboldt Current comes
all the way up from Antarctica,

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00:20:31,550 --> 00:20:33,883
bringing with it cold water,

230
00:20:33,883 --> 00:20:40,428
and it is this cold water which creates
this dull grey day that we see here,

231
00:20:40,428 --> 00:20:41,887
with a fog overlying us.

232
00:20:46,055 --> 00:20:50,015
It causes the air above it
to cool, forming a thick bank

233
00:20:50,015 --> 00:20:53,641
of cold cloud and fog
which clings to the shore.

234
00:20:55,267 --> 00:20:59,143
Hot, dry air descends at the tropics.

235
00:20:59,143 --> 00:21:05,604
Here, that hot air sits on top of the cold,
heavy rainclouds, holding them down.

236
00:21:05,604 --> 00:21:09,314
Meteorologists call this
an inversion layer.

237
00:21:09,314 --> 00:21:14,858
Trapped at 3,000 feet, the clouds
can't rise up and shed their rain

238
00:21:14,858 --> 00:21:16,734
on the high-altitude desert.

239
00:21:18,568 --> 00:21:20,985
The inversion layer
prevents any moisture

240
00:21:20,985 --> 00:21:25,279
that may accumulate close to the sea
from moving inland.

241
00:21:25,279 --> 00:21:27,404
So that is one of the reasons

242
00:21:27,404 --> 00:21:31,947
why this Humboldt Current
actually contributes to the dryness

243
00:21:31,947 --> 00:21:36,366
of the Atacama Desert
that we see just over there.

244
00:21:39,034 --> 00:21:44,202
But is it this inversion layer,
created by the Humboldt Current,

245
00:21:44,202 --> 00:21:50,580
that has turned Atacama
into the driest desert in the world?

246
00:21:50,580 --> 00:21:52,873
In the desert's northern tip,

247
00:21:52,873 --> 00:21:57,040
in a desolate place
called Quebrada Aroma,

248
00:21:57,040 --> 00:22:03,002
geologist Laura Evenstar
is looking for clues to solve this riddle.

249
00:22:03,002 --> 00:22:08,378
She's trying to put a date on
when the desert became so very dry.

250
00:22:11,380 --> 00:22:14,881
Other deserts, like the Mojave,
don't get much rain,

251
00:22:14,881 --> 00:22:17,841
but when they do, it's dramatic.

252
00:22:17,841 --> 00:22:21,676
Storms bring heavy rains
and flash floods.

253
00:22:23,301 --> 00:22:28,720
But not here in the Quebrada Aroma,
which is now totally dry.

254
00:22:30,345 --> 00:22:33,888
One way to date the last time there
would have been enough rainfall

255
00:22:33,888 --> 00:22:38,015
to cause a flash flood
is to try to find out

256
00:22:38,015 --> 00:22:43,017
how long the rocks have been
lying there undisturbed.

257
00:22:43,017 --> 00:22:46,644
What we have here is a miniature
demonstration of what goes on

258
00:22:46,644 --> 00:22:49,269
if you start having large amounts
of rainfall.

259
00:22:49,269 --> 00:22:51,937
So, this is our rainfall here...

260
00:22:55,855 --> 00:23:00,648
...and what we can see is that when
we start raining on our desert surface,

261
00:23:00,648 --> 00:23:02,899
it'll pick up the boulders
and move them around

262
00:23:02,899 --> 00:23:06,985
and then when there's no water here,
the boulders just sit still and don't move.

263
00:23:11,445 --> 00:23:15,362
The surface of Quebrada Aroma
is strewn with rocks,

264
00:23:15,362 --> 00:23:18,697
so she's cracking them open
to reveal evidence

265
00:23:18,697 --> 00:23:23,616
of exactly when water
last flooded the landscape.

266
00:23:23,616 --> 00:23:25,700
(CLANGING)

267
00:23:28,325 --> 00:23:31,118
What we do is we have to knock
a bit off, and then we examine it

268
00:23:31,118 --> 00:23:34,828
and have a look at whether
it's got a... a very dark colour,

269
00:23:34,828 --> 00:23:37,413
and hopefully we can be able to see
some of the black minerals,

270
00:23:37,413 --> 00:23:39,289
which is what we're looking for.

271
00:23:42,206 --> 00:23:46,249
The tiny black crystalline
minerals are pyroxenes.

272
00:23:49,917 --> 00:23:55,336
They're crucial evidence because,
like microscopic geologic clocks,

273
00:23:55,336 --> 00:24:01,172
their chemistry changes when
exposed to cosmic radiation over time.

274
00:24:02,422 --> 00:24:04,965
The sun is only producing
a tiny bit of the radiation

275
00:24:04,965 --> 00:24:06,591
which will hit this rock,

276
00:24:06,591 --> 00:24:10,467
the majority of it is coming from
all the stars you see in the night sky.

277
00:24:10,467 --> 00:24:14,260
What it does to the rock
is basically, uh, just bakes it,

278
00:24:14,260 --> 00:24:20,262
a bit like a really bad suntan, so it
just comes down, hits it and cooks it.

279
00:24:21,513 --> 00:24:24,889
As the rock gets cooked
by cosmic rays,

280
00:24:24,889 --> 00:24:30,141
the pyroxenes break down
and produce a gas called helium-3.

281
00:24:31,642 --> 00:24:34,768
We can record how much
helium-3 is within this rock,

282
00:24:34,768 --> 00:24:38,561
and the more we have,
the longer that it has been exposed

283
00:24:38,561 --> 00:24:42,021
to cosmic or, uh, solar radiation.

284
00:24:43,979 --> 00:24:48,482
Helium-3 gas is only produced
in microscopic quantities.

285
00:24:51,108 --> 00:25:01,445
So Evenstar takes her samples to a lab
7,000 miles away in Glasgow, Scotland.

286
00:25:10,740 --> 00:25:16,409
So what we do, uh, using a laser is
we shoot the laser into one of the wells,

287
00:25:16,409 --> 00:25:19,160
and vaporise our crystals.

288
00:25:22,495 --> 00:25:24,162
And that's releasing the helium-3,

289
00:25:24,162 --> 00:25:27,955
then the helium-3 is going to go through
all this complicated machinery,

290
00:25:27,955 --> 00:25:30,748
eventually run through
the mass spectrometer.

291
00:25:32,915 --> 00:25:34,458
By analysing this data,

292
00:25:34,458 --> 00:25:39,085
she can figure out the last time
the boulders were moved.

293
00:25:41,251 --> 00:25:46,504
The oldest age sample we've actually
recorded has been 23 million years.

294
00:25:46,504 --> 00:25:51,756
So what this means is that, within
certain areas of the Atacama Desert,

295
00:25:51,756 --> 00:25:53,757
these boulders have been sitting there

296
00:25:53,757 --> 00:25:56,758
and not moved by water
for 23 million years.

297
00:25:59,301 --> 00:26:02,843
So the Atacama Desert is one of the
oldest undisturbed surfaces in the world.

298
00:26:02,843 --> 00:26:07,846
These boulders were there
before humans even started to exist,

299
00:26:07,846 --> 00:26:09,263
they are incredibly old.

300
00:26:13,056 --> 00:26:15,849
Evenstar has discovered that
there are places in the desert

301
00:26:15,849 --> 00:26:20,058
which have been bone dry
for 23 million years.

302
00:26:23,268 --> 00:26:27,020
This date is a crucial clue
in the investigation,

303
00:26:27,020 --> 00:26:31,646
because it coincides with the birth
of the Humboldt Current.

304
00:26:32,647 --> 00:26:36,689
South America
was once joined to Antarctica.

305
00:26:36,689 --> 00:26:41,109
But, roughly 25 million years ago,
these continents split.

306
00:26:41,109 --> 00:26:43,943
A channel opened.

307
00:26:43,943 --> 00:26:47,735
Freezing water began
to circulate round the pole,

308
00:26:47,735 --> 00:26:50,987
and thundered north along the coast.

309
00:26:52,446 --> 00:26:55,572
This cold current
formed an inversion layer,

310
00:26:55,572 --> 00:27:00,491
trapping coastal rainclouds and
starting Atacama's slow transformation

311
00:27:00,491 --> 00:27:03,867
into the driest place in the world.

312
00:27:11,328 --> 00:27:15,580
But the Humboldt Current
is not the only culprit.

313
00:27:15,580 --> 00:27:19,623
Ironically, the quest to find out
how the desert became so dry

314
00:27:19,623 --> 00:27:24,750
comes up against one of
the wettest places on Earth.

315
00:27:24,750 --> 00:27:27,751
On the other side of Atacama
is the Amazon,

316
00:27:27,751 --> 00:27:33,961
but the heavy rainfall from the rainforest
doesn't get anywhere near the desert.

317
00:27:33,961 --> 00:27:37,297
The reason why is in plain sight.

318
00:27:37,297 --> 00:27:40,506
Between the Amazon
and the Atacama Desert

319
00:27:40,506 --> 00:27:43,924
lies the vast Andes mountain range.

320
00:27:43,924 --> 00:27:48,842
Geologic evidence suggests
the Andes finally grew high enough,

321
00:27:48,842 --> 00:27:54,470
some ten million years ago, to prevent
any rain from reaching the desert.

322
00:27:54,470 --> 00:28:00,472
It's called a rainshadow effect, and it's
the final factor which drove Atacama

323
00:28:00,472 --> 00:28:03,556
to become the driest place on Earth.

324
00:28:08,517 --> 00:28:13,185
The evidence for what turned Atacama
so incredibly dry is mounting.

325
00:28:15,019 --> 00:28:20,313
The Humboldt Current creates
a weather system that allows no rainfall.

326
00:28:20,313 --> 00:28:24,981
Helium-3 in rocks shows
that the process of desiccation

327
00:28:24,981 --> 00:28:27,899
began 23 million years ago.

328
00:28:29,358 --> 00:28:33,735
The rising Andes, ten million
years ago, made it drier still.

329
00:28:35,527 --> 00:28:39,362
The investigation would
seem to be conclusive.

330
00:28:39,362 --> 00:28:41,654
Atacama has been a barren,

331
00:28:41,654 --> 00:28:45,197
essentially rainless landscape
for millions of years.

332
00:28:46,740 --> 00:28:51,367
But then something happened to
blow that conclusion wide open.

333
00:28:51,367 --> 00:28:58,244
Tiny shards of stone revealed that
an ancient civilisation once lived here.

334
00:28:59,578 --> 00:29:04,747
But how could people live
in the world's driest desert?

335
00:29:10,832 --> 00:29:16,668
The Atacama Desert is by far
the driest place on Earth,

336
00:29:16,668 --> 00:29:19,878
and by piecing together the evidence,

337
00:29:19,878 --> 00:29:24,588
scientists believed
it had been so for millions of years.

338
00:29:31,799 --> 00:29:36,175
Yet, at a remote site
called Guanaqueros,

339
00:29:36,175 --> 00:29:42,137
paleoecologist Claudio Latorre
made an intriguing discovery

340
00:29:42,137 --> 00:29:45,846
which paints a more complex picture.

341
00:29:47,138 --> 00:29:49,431
This is, uh, an extraordinary find,

342
00:29:49,431 --> 00:29:51,848
and this was probably
a little knife or a scraper

343
00:29:51,848 --> 00:29:53,766
that's been broken off and discarded.

344
00:29:53,766 --> 00:29:55,975
That could probably still cut.

345
00:29:55,975 --> 00:30:00,684
To the untrained eye,
it looks like a simple rock shard,

346
00:30:00,684 --> 00:30:04,394
but Latorre can see
it's been worked into a tool.

347
00:30:07,104 --> 00:30:09,730
And he's found hundreds of them.

348
00:30:09,730 --> 00:30:14,357
They're clues that reveal
ancient humans once lived here.

349
00:30:15,358 --> 00:30:17,108
This was not just
a temporary residence,

350
00:30:17,108 --> 00:30:19,192
this was something
where people were living

351
00:30:19,192 --> 00:30:20,901
and working and banging away at rocks

352
00:30:20,901 --> 00:30:24,027
and making artefacts
and living off this landscape,

353
00:30:24,027 --> 00:30:25,986
using the resources at hand.

354
00:30:30,571 --> 00:30:33,239
As water is essential for life,

355
00:30:33,239 --> 00:30:38,991
it seems impossible that any kind
of plant, animal or human life

356
00:30:38,991 --> 00:30:40,617
could survive here.

357
00:30:41,868 --> 00:30:47,370
Latorre suspects that some regions
of this 57,000-square-mile desert

358
00:30:47,370 --> 00:30:49,912
were once much wetter.

359
00:30:49,912 --> 00:30:55,414
Not millions of years ago, but during
the time humans walked the Earth.

360
00:30:57,290 --> 00:31:03,042
In 1997, he set off on a mission
to hunt for evidence.

361
00:31:03,042 --> 00:31:06,335
Today, he's retracing that journey.

362
00:31:06,335 --> 00:31:11,087
Changes in the climate
can be seen in the rocks,

363
00:31:11,087 --> 00:31:15,172
so Latorre examines the cliff
layer by layer.

364
00:31:15,172 --> 00:31:19,298
He finds a crucial piece of evidence.

365
00:31:22,675 --> 00:31:25,926
This is actually where the
interesting part of the story comes in.

366
00:31:25,926 --> 00:31:30,095
This chalky rock
is called diatomite.

367
00:31:34,471 --> 00:31:38,764
It's made from the crushed
remains of fossilised algae,

368
00:31:38,764 --> 00:31:42,766
microscopic life forms
which only live in freshwater.

369
00:31:44,141 --> 00:31:47,142
What this rock is telling us
is that we had basically a wetland.

370
00:31:52,352 --> 00:31:55,145
Whereas you look at the
landscape across today

371
00:31:55,145 --> 00:31:59,356
and we see that it's basically
about as dry as you can get.

372
00:32:04,357 --> 00:32:10,109
Sometime in the past there was water
on the surface of the desert.

373
00:32:10,109 --> 00:32:14,945
Latorre's next task was to find out when.

374
00:32:14,945 --> 00:32:18,947
Radiocarbon dating is one of
the most accurate methods of dating,

375
00:32:18,947 --> 00:32:24,115
but using this method means
sampling something organic.

376
00:32:24,115 --> 00:32:27,699
So Latorre combed the desert for clues.

377
00:32:29,034 --> 00:32:31,827
The way we work
is basically poking our heads

378
00:32:31,827 --> 00:32:35,161
into every little hole and crevice
that we can find.

379
00:32:35,161 --> 00:32:38,204
When we found this place,
we couldn't believe our eyes.

380
00:32:40,538 --> 00:32:43,456
He accidentally
and luckily stumbled upon

381
00:32:43,456 --> 00:32:47,832
the most important piece of evidence
in this investigation.

382
00:32:47,832 --> 00:32:52,542
At the back of the cave was a vast nest.

383
00:32:54,043 --> 00:32:59,170
It's made from the faeces of thousands
of generations of tiny mammals.

384
00:33:00,588 --> 00:33:02,671
The size and shape of the pellets

385
00:33:02,671 --> 00:33:07,090
told Latorre those animals
were chinchilla rats.

386
00:33:07,090 --> 00:33:08,757
(SQUEAKING)

387
00:33:10,383 --> 00:33:19,011
And it also contained the critical clue
he was searching for - organic material.

388
00:33:19,011 --> 00:33:20,762
When we found this site,

389
00:33:20,762 --> 00:33:22,805
one of the most exciting
discoveries that we made

390
00:33:22,805 --> 00:33:26,264
was the fact that it's full of grasses.

391
00:33:26,264 --> 00:33:30,390
Now, look across the landscape today
and tell me where those grasses are,

392
00:33:30,390 --> 00:33:31,850
and we immediately knew

393
00:33:31,850 --> 00:33:35,226
that we were talking about
some major vegetation change.

394
00:33:35,226 --> 00:33:39,894
This grass looks as fresh and crisp
as if it was collected yesterday.

395
00:33:39,894 --> 00:33:44,021
But when Latorre carbon-dated grass
from the nest,

396
00:33:44,021 --> 00:33:46,438
what he found was amazing.

397
00:33:46,438 --> 00:33:50,940
The grass was more than
11,000 years old.

398
00:33:53,691 --> 00:33:57,735
What I have in my hands here
is an ancient ecosystem.

399
00:33:57,735 --> 00:34:00,693
This is about as clear an indicator
you can get,

400
00:34:00,693 --> 00:34:03,070
better than anything else
you can think of,

401
00:34:03,070 --> 00:34:06,029
that water increased
in the past in this area.

402
00:34:08,739 --> 00:34:14,491
The nest reveals strong evidence that
plants and mammals did exist here,

403
00:34:14,491 --> 00:34:17,117
and they weren't alone.

404
00:34:18,159 --> 00:34:22,244
Underneath the thick layer
of nest is another layer,

405
00:34:22,244 --> 00:34:26,162
rich with tiny handmade tools.

406
00:34:26,162 --> 00:34:28,746
If we look around, you know,

407
00:34:28,746 --> 00:34:31,998
we can find actually evidence
of this past human occupation,

408
00:34:31,998 --> 00:34:35,541
there's just... full of little shards
here on the floor.

409
00:34:36,625 --> 00:34:42,960
Some regions of Atacama have been
constantly dry for 23 million years.

410
00:34:42,960 --> 00:34:48,546
But this evidence shows that
other regions, like Guanaqueros,

411
00:34:48,546 --> 00:34:51,130
were very different 11,000 years ago.

412
00:34:54,381 --> 00:35:01,092
It's a fossilised snapshot of a diverse
ecosystem briefly bursting into life.

413
00:35:01,092 --> 00:35:06,511
Grasses grow and wetlands flourish
in this wetter time.

414
00:35:06,511 --> 00:35:09,679
Tiny mammals thrive and breed,

415
00:35:09,679 --> 00:35:15,223
while game like vicu�a and llamas
meant humans could live

416
00:35:15,223 --> 00:35:18,265
in this rich and fertile environment.

417
00:35:19,724 --> 00:35:21,933
So it's wonderful to know that,

418
00:35:21,933 --> 00:35:25,435
by looking at something
as mundane as, uh, a rodent nest,

419
00:35:25,435 --> 00:35:30,728
you can actually find clues
that enable you to understand

420
00:35:30,728 --> 00:35:33,688
the past human colonisation
of the Atacama Desert,

421
00:35:33,688 --> 00:35:39,148
which is no mean feat in itself, given the
fact that it's such a harsh climate today.

422
00:35:43,109 --> 00:35:47,694
The date of the rat's nest
gives scientists a possible theory

423
00:35:47,694 --> 00:35:49,735
of where the water came from.

424
00:35:53,196 --> 00:35:58,614
11,000 years ago,
the last Ice Age was at an end.

425
00:36:00,240 --> 00:36:02,074
The global climate was changing.

426
00:36:05,909 --> 00:36:11,745
More rain fell high in the Andes,
flowing down to the desert in rivers.

427
00:36:13,287 --> 00:36:18,538
In some places, groundwater pooled,
forming wetlands.

428
00:36:18,538 --> 00:36:24,624
Others remained untouched by water,
as they had for millions of years.

429
00:36:26,250 --> 00:36:31,335
But, just a thousand years later,
the climate changed again.

430
00:36:31,335 --> 00:36:33,336
Rivers dried up.

431
00:36:33,336 --> 00:36:35,629
Grasses died.

432
00:36:35,629 --> 00:36:38,629
Rats and humans disappeared.

433
00:36:38,629 --> 00:36:42,173
Now, every drop of groundwater
has been sucked down

434
00:36:42,173 --> 00:36:44,423
into the parched earth.

435
00:36:44,423 --> 00:36:49,342
Latorre demonstrates
how deep that water is today.

436
00:36:50,801 --> 00:36:54,552
So, just to give you an idea
of how much change has gone on

437
00:36:54,552 --> 00:36:58,053
since the wetland was
formerly at the surface,

438
00:36:58,053 --> 00:37:00,054
here's a little experiment
that we can do.

439
00:37:00,054 --> 00:37:02,514
This is a well,
and I'll drop this little rock,

440
00:37:02,514 --> 00:37:05,098
and we're going to count
and we're going to see how long it takes

441
00:37:05,098 --> 00:37:06,724
for that rock to hit the water.

442
00:37:10,559 --> 00:37:11,934
(SPLASH)

443
00:37:11,934 --> 00:37:15,269
So that takes almost four seconds
to reach the water,

444
00:37:15,269 --> 00:37:20,354
that's well over 200 feet below the
surface is where the water table is today.

445
00:37:20,354 --> 00:37:23,731
It's about as dry as it gets.
It's what we call absolute desert.

446
00:37:23,731 --> 00:37:30,357
No plants, no wildlife, nothing,
no surface running water whatsoever.

447
00:37:33,901 --> 00:37:39,486
The investigation of this driest place
on Earth took a surprising turn.

448
00:37:40,737 --> 00:37:43,863
Tools show humans lived here.

449
00:37:43,863 --> 00:37:48,948
Diatomite reveals the climate
was once wetter.

450
00:37:48,948 --> 00:37:55,492
Rats' dung and grass dates a diverse
ecosystem to 11,000 years ago.

451
00:37:56,868 --> 00:38:00,953
Yet this extraordinary desert
has more secrets to tell,

452
00:38:00,953 --> 00:38:06,580
not just about life in one of the most
extreme environments on our planet,

453
00:38:06,580 --> 00:38:09,997
but also about life on other planets.

454
00:38:17,626 --> 00:38:23,295
Today, scientists suspect
Atacama is the driest it has ever been,

455
00:38:23,295 --> 00:38:30,547
so they're investigating whether there's
any source of water left here at all.

456
00:38:31,548 --> 00:38:36,467
And NASA scientist Alfonso Davila
knows that if there's water,

457
00:38:36,467 --> 00:38:39,968
there's a chance there could be life
here too.

458
00:38:39,968 --> 00:38:44,344
But when he first arrived,
the signs didn't look good.

459
00:38:45,345 --> 00:38:47,471
When I came here
for the first time,

460
00:38:47,471 --> 00:38:50,013
I drove for a couple of thousand miles,

461
00:38:50,013 --> 00:38:52,931
and when I got back to my base camp,

462
00:38:52,931 --> 00:38:58,099
I realised that I didn't have a single
insect smashed against my windshield.

463
00:38:58,099 --> 00:39:00,434
That has never happened to me
anywhere else in the world

464
00:39:00,434 --> 00:39:03,227
and I... and I think
that's a very good example

465
00:39:03,227 --> 00:39:06,645
of, uh, how hard
this environment is for life.

466
00:39:07,645 --> 00:39:12,980
Since the 1960s, NASA scientists
have been hunting for bacteria life

467
00:39:12,980 --> 00:39:17,774
in the desert's thin soils,
yet they found nothing...

468
00:39:19,399 --> 00:39:24,776
...until 2005, when they came across
a strange white landscape.

469
00:39:28,070 --> 00:39:32,113
By chance, one of Davila's colleagues
picked up a rock,

470
00:39:32,113 --> 00:39:37,906
smashed it open and discovered
something completely unexpected.

471
00:39:39,157 --> 00:39:44,785
Yeah, you can see very nicely
a... a green layer inside the crust.

472
00:39:47,160 --> 00:39:51,829
Under the microscope,
the significance of this pale green blur

473
00:39:51,829 --> 00:39:53,871
zoomed sharply into focus.

474
00:39:55,204 --> 00:40:00,415
To our surprise, we saw a green
microorganism living inside the rock.

475
00:40:00,415 --> 00:40:03,292
So that came as a big surprise, uh,

476
00:40:03,292 --> 00:40:05,500
because nobody was expecting
microorganisms

477
00:40:05,500 --> 00:40:08,460
in the middle of the driest place
on Earth.

478
00:40:10,711 --> 00:40:17,672
Completely by accident, hidden inside
a rock they'd discovered life.

479
00:40:19,714 --> 00:40:23,382
This mineral is, uh, sodium chloride,
otherwise known as halite.

480
00:40:23,382 --> 00:40:26,800
It's a very common mineral
in the Atacama Desert

481
00:40:26,800 --> 00:40:29,843
and it's also a very common mineral
in kitchens around the world,

482
00:40:29,843 --> 00:40:33,678
as this is exactly the same salt
we use to spice our food.

483
00:40:36,262 --> 00:40:40,014
Salt can preserve food
by killing off bacteria.

484
00:40:40,014 --> 00:40:47,433
But here, strangely, it was harbouring
a colony of green microbes.

485
00:40:47,433 --> 00:40:51,268
To find out how they survive,

486
00:40:51,268 --> 00:40:55,311
Davila laid out a series of sensors
that measure humidity.

487
00:40:57,312 --> 00:41:00,771
His research shows that,
although, on average,

488
00:41:00,771 --> 00:41:05,732
the air in the desert
is around 10% humidity,

489
00:41:05,732 --> 00:41:11,025
on rare occasions,
it rises as high as 75%.

490
00:41:13,026 --> 00:41:18,570
This momentary increase in water
vapour is the only source of water.

491
00:41:20,821 --> 00:41:25,698
And it's this water that gives rise to life.

492
00:41:25,698 --> 00:41:31,367
The distinctive property of salt is
its capability to extract water vapour

493
00:41:31,367 --> 00:41:34,535
from the atmosphere and forms
a liquid solution inside the rock.

494
00:41:36,077 --> 00:41:39,578
As moisture from the air
is sucked into the salt,

495
00:41:39,578 --> 00:41:44,622
the microbes allow the rock
to bring the water to them.

496
00:41:46,581 --> 00:41:50,124
Life is actually very robust,
it's, uh, very flexible

497
00:41:50,124 --> 00:41:54,001
and it can really adapt to some
of the most extreme conditions

498
00:41:54,001 --> 00:41:55,668
that we see on Earth.

499
00:42:01,504 --> 00:42:06,380
NASA believes this discovery in the
Atacama Desert can reveal something

500
00:42:06,380 --> 00:42:08,798
about life on Mars.

501
00:42:11,174 --> 00:42:18,468
In 1976, the Viking Lander detected
water in Mars's thin atmosphere.

502
00:42:22,679 --> 00:42:30,182
In 2008, NASA's Mars Odyssey
orbiter found evidence of salt

503
00:42:30,182 --> 00:42:32,390
on the planet's surface.

504
00:42:32,390 --> 00:42:34,558
(RADIO STATIC)

505
00:42:34,558 --> 00:42:36,183
(RADIO CHATTER)

506
00:42:37,226 --> 00:42:41,102
Now, when humans
finally get to Mars,

507
00:42:41,102 --> 00:42:42,686
they won't be looking for life

508
00:42:42,686 --> 00:42:44,812
in the thin Martian soils...

509
00:42:47,688 --> 00:42:50,064
...but inside the rocks.

510
00:42:52,898 --> 00:42:56,733
Unfortunately, it's gonna be a long time
until we see humans walking on Mars.

511
00:42:56,733 --> 00:43:02,360
Until then, we come to the Atacama
Desert, and we study this type of rocks,

512
00:43:02,360 --> 00:43:05,569
which likely hold the clue to
understanding life on Earth

513
00:43:05,569 --> 00:43:08,195
and also to understanding
the potential for life

514
00:43:08,195 --> 00:43:10,238
in other planets in our solar system.

515
00:43:12,155 --> 00:43:15,573
So it's possible
that an accidental discovery

516
00:43:15,573 --> 00:43:17,407
in the driest place on Earth

517
00:43:17,407 --> 00:43:21,868
will one day lead scientists
to crack open a Martian rock

518
00:43:21,868 --> 00:43:25,077
and discover little green alien life.

519
00:43:35,790 --> 00:43:40,375
The investigation into how the
driest place on Earth was made

520
00:43:40,375 --> 00:43:46,794
has revealed an awesome Earth story
spanning 150 million years.

521
00:43:48,836 --> 00:43:55,047
Gypsum, a rock which forms in water,
shows the desert was once a sea bed.

522
00:43:55,047 --> 00:43:59,882
Hot geysers show that immense
volcanic activity under the desert

523
00:43:59,882 --> 00:44:02,384
raised it above the ocean.

524
00:44:03,509 --> 00:44:07,719
Tiny pyroxene crystals reveal
the first areas of the desert

525
00:44:07,719 --> 00:44:11,886
which became completely dry
23 million years ago.

526
00:44:13,054 --> 00:44:17,430
Rat nests reveal a small pocket of life
that bloomed in the desert

527
00:44:17,430 --> 00:44:19,807
at the end of the last Ice Age.

528
00:44:21,058 --> 00:44:27,684
Tiny green organisms in salt
show that even here, life clings on.

529
00:44:29,477 --> 00:44:35,855
Today this place is unique on Earth -
absolute perfect desert,

530
00:44:35,855 --> 00:44:40,023
and the investigation
into how it formed has shed light

531
00:44:40,023 --> 00:44:45,483
on another chapter in the story
of how the Earth was made.