>> Earth, a unique planet,
restless and dynamic.
Continents shift and clash,
volcanoes erupt.
Glaciers grow and recede,
titanic forces
that are constantly at work,
leaving a trail of geological
mysteries behind, none greater
than the Sahara desert--the
hottest place on the planet, a
deadly wasteland that time
forgot, or so scientists
believed till they unearthed a
series of startling clues--the
fossils of sea creatures,
freshwater shells buried in
sand, ancient settlements with
human remains--clear evidence
that this stark landscape hides
a turbulent past, one that would
alter the course of human
history and provide a dramatic
new chapter in the story of how
The Earth Was Made. S02x04 Sahara Original Air Date on December 15, 2009
-- Sync, corrected by elderman -- -- for www.addic7ed.com --
Africa's vast Sahara desert is
as big as the United States.
The sand alone from this giant
expanse could bury the entire
world 8 inches deep.
It's the largest desert and the
hottest place on Earth.
>> When I first arrived in the
Sahara, I was just struck by how
utterly barren it was.
It's like the color green was
removed from the palette when
they made this place. Just
nothing, grays and browns and
not a scrap of life.
>> Smith's mission is to unearth
evidence of what made the Sahara
into the wasteland it is today.
Her investigation begins on the
desert's far eastern edge in
Egypt, not in the sands of the
Sahara, but in one of the most
epic structures ever built by
man--the great pyramids.
The building blocks of this
ancient wonder house a
remarkable clue to the history
of this land from a time long
before the pharaohs even
existed.
>> So, taking a closer look at
these blocks making up the
Pyramids, there's actually these
gorgeous marine fossils in here.
Most obvious are these flat
disks, up to about an inch wide.
They're called nummulites, and
they're actually single-celled
organisms.
>> The name nummulites means
little coins in Latin.
They are some of the largest
single-celled
creatures to have ever existed.
In ancient times, these blocks
were cut from quarries across
the country and dragged to the
pyramid site.
Each block weighed 2 1/2 tons,
and it took two million of them,
and over 20 years, to build the
Great Pyramid,
and, incredibly, up to 40% of
each building block is made up
of the bodies of ancient sea
creatures like these.
What's even more important about
the marine nummulites is that
they date back 40 million years
and they only lived in water.
>> It's a piece of evidence that
this area, now desert, was once
underneath the ocean.
You think about the
construction of the pyramid, but
not necessarily about what it's
made of and these gorgeous
fossils.
>> The Sahara now is the world's
biggest dustbowl, but the tiny
nummulites fossils suggest that
it was once very different,
that perhaps there could have
been water in this barren
wilderness.
Smith heads further inland to
investigate this extraordinary
idea.
She travels to a remote desert
valley near where the pyramid
stones were quarried.
It's called Wadi al Hitan.
Spread out in the sand lie
hundreds of fossils, first
excavated in 1983, but these are
nothing like the tiny
nummulites.
>> That's a whale.
So, here's the backbone, the
vertebrae.
Here's some ribs, the shoulder,
part of the front fin, and there
are the jaws.
This guy definitely did not live
in a desert.
>> This incredible fossil is a
Dorudun, an ancestor of modern
whales, one that died out 36
million years ago.
>> So, based on the size of
these vertebrae and how much of
the animal was here, it was
probably about 21 feet long.
This guy tells us that we were
underwater.
We were in the middle of an
ocean.
>> Wadi al Hitan is Arabic for
Valley of the Whales.
This 12-mile
dip in the landscape has the
highest concentration of fossils
in the world.
Some were found in the desert
floor, others in the cliff
walls.
The count so far is 400.
Almost all are marine animals,
further evidence that the Sahara
was once covered by sea.
>> So, here we've got the fossil
of a baby whale.
You can see the lower jaw down
here with some teeth and the
shoulder, the backbone, some
ribs and all curled around.
Actually, the tail comes right
back to near the head.
>> As if finding whales in the
desert wasn't intriguing enough,
there's yet another mystery to
be solved.
A lot of the fossils are of very
young dorudons, like this one.
A delicate mesh of stone helps
explain why so many baby whales
died in this place.
>> Wow, so finding that whale
fossil told us we were in the
ocean.
These rocks acutally tell us a
lot more about what type of
ocean we were dealing with.
These are all fossilized
mangrove roots.
>> These roots would have been
below water.
The mangrove trees would have
risen above it.
>> Since trees don't grow out of
the deep ocean, we know that
this area was actually under
shallow ocean at the time these
rocks were deposited, something
probably that looked like the
Florida Everglades, where there
are mangroves growing now.
>> Smith has discovered the
shoreline of the ancient sea.
The shallowness of the water
could explain why there were so
many young animals here.
>> So, one idea--there's a bunch
of these baby whale fossils
found in this area, and
this would have been a
shallow protected bay that maybe
the whales came just to birth
their young.
It is absolutely incredible to
see a fossilized whale in a
place that, right now, gets less
than a millimeter of rainfall a
year.
It's as much convincing evidence
for geologic change as I can
imagine.
>> The pieces of the puzzle are
coming together to reveal the
Sahara's watery past.
>> So, 40 million years ago,
this desert would have been
covered in the middle of this
valley by a shallow bay,
probably a brilliant tropical
blue-green color.
The shoreline would have been
off along the horizon, some
mangrove trees in the shallowest
parts of it.
>> Inland would have been a
vibrant combination of
rainforest and swampland.
The whales would have been drawn
to this ancient shore because of
the plentiful supply of food,
but their ocean is about to
vanish.
Marine fossils found in
Europe and Africa are evidence
that this ocean stretched almost
halfway around the world and
connectedAasia to the Atlantic.
It's called the Tethys Sea, and
much of the Sahara was submerged
under it.
The mystery is how and when this
lush water world turned into the
barren wasteland we see today.
The answer lies not in climate
patterns, but in geology.
The entire African continent
is underpinned by a giant piece
of the Earth's crust.
It's called a tectonic plate,
and 40 million years ago, in
what is known as the Eocene Age,
it was on the move.
>> So, at Wadi al Hitan, we have
whales swimming around in this
Eocene Ocean.
All the while, the African plate
is moving to the north.
Africa collides with Europe,
closing the Tethys Sea, but the
African plate keeps moving
>> So we uplifted the northern
part of Africa,
and so the Tethys Sea recedes,
and we've got this whole area of
North Africa now emerged.
It's out on land.
>> The whales of Wadi al Hitan
are cut off and trapped in
smaller and smaller pools of
water.
The deadly Sahara has claimed
its first victims.
In the quest to discover the
history of the vast Sahara
Desert, geologists have so far
uncovered two important clues.
Sea fossils in the great
Pyramids of Egypt show these
building blocks were once
underwater.
Whale bones reveal that a sea
submerged much of the Sahara 37
million years ago.
As the forces of plate tectonics
pushed the Sahara out from under
the sea, it created a tropical
swamp.
In order to figure out what made
it into the wasteland visible
today, scientists have to
pinpoint the moment of its
birth, but the clues to this
mystery turn out to be hidden in
the last place anyone expected.
>> 20 million years ago, the
Sahara desert was a lush
tropical swamp.
Geologists are now piecing
together the story of the next
20 million years.
Today the Sahara lies in what is
known as the desert belt, a
region of dry air north of the
equator.
Here, strong winds clear the sky
of clouds and dry out the land
below.
It stretches through the Gobi
Desert in China and across the
deserts of the southwestern
United States.
The Sahara is the largest, and
yet geologists know next to
nothing about when it was
created.
>> What we have are just these
little bits and pieces, these
snapshots of what the Sahara was
like, because the wind blows
away a lot of our record, and
what isn't blown away is often
covered by sand.
So, it's kind of hard to find
the rocks we need to tell the
story we're trying to tell.
>> One of the few places that
shelters a clue to the Sahara's
birth is the white desert.
In this hauntingly beautiful
site, dramatic shapes have been
sculpted out of rock.
>> Oh, this is great.
It's got that mushroom shape.
>> These structures are called
Yardangs, and they are a kind of
hourglass that could help
measure the age of the desert.
>> This rock is another
piece of evidence that this
desert was once under the ocean.
It's actually a chalk made up of
billions of little marine
micro-organisms.
These chalks are actually really
easy to erode, so that's one
reason things are so beautifully
sculpted by the wind.
>> But the wind is a brutal
creator.
It picks up sand and hurls it at
the Yardang.
>> When wind scours or
sandblasts the rocks, this is
the characteristic shape that we
get, this mushroom shape,
narrower in the middle.
That's because the wind goes
faster as you move up from the
ground, so it can erode harder,
but it has less sand in it
since it picks up the sand from
the ground.
So, where we get the most
erosion, where the rock is
narrowest, is where we have the
best mix of fast wind and the
most sand.
>> 40 million years ago, the top
of the Yardangs formed part of
the solid sea floor, but the
wind picked up once the Sahara
turned to desert, and the
process of carving out these
shapes began.
Figuring out how long that took
could help pinpoint the age of
the desert.
>> It's hard to say precisely
how long it would take for the
wind to carve this all out.
Something like this about 15
feet high, soft rock, you're
looking at maybe only tens to a
few hundreds of thousand of
years, but to carve out the
whole oasis depression, you've
got to need at least a million
years.
>> But geologists suspect the
Sahara is older than a million
years.
In their search for a more
accurate date, they next turn to
its most iconic feature--
Sand dunes.
Here in the Sahara, sandstorms
kick up that can last for 4
days.
The sand is hurled across the
terrain.
Over hundreds of thousands of
years, it accumulates into dunes
that can tower 50 stories high.
Perhaps these mountains of sand
hold the secret of the desert's
great age.
>> As soon as the climate
becomes arid, you can start
building dunes, and if we want
to know how long that took, we
can try and date the dunes
themselves, but that's really
hard.
>> What's hard is that these
dunes are constantly shifting.
The wind that builds them also
blows them away, moving them an
average of 50 feet a year.
To get a precise age for the
desert, scientists need to
follow the sand to the end of
its journey.
>> Coarse sand travels slowly
and doesn't go all that far, but
the finer particles will
actually travel further, and so
dust-sized particles actually
can get carried out into the
Atlantic.
>> The Sahara is the largest
source of dust on the planet.
500 million tons of it ends up
in the Atlantic every year.
Some of it reaches as far as
Florida and creates spectacular
red sunsets, but much of it
settles on the ocean floor, a
treasure trove of information
about the Sahara's past.
>> What's wonderful about
working with the ocean sediments
is that they capture everything.
They're this very faithful
recorder of the sediments that
are raining down from the
surface.
>> In 1995, Demenocal drilled
down into the ocean floor
through layers of mud dating
back millions of years.
Each layer of sediment is like a
time capsule.
Shallow levels show plenty of
this dust blown over from the
desert.
So, Demenocal extracted deeper
core samples from over a million
years ago.
Still there was desert dust.
Finally, he dug down to a layer
that was laid down 3 million
years ago, and there the dust
finally stopped.
It had taken a voyage to the
ocean floor to uncover the
turning point from humid,
tropical landscape into searing
desert.
>> That's a pretty amazing
change.
You don't think of something as
large and expansive and fixed as
the Saharan desert as being
something capable of such
profound changes, and yet this
is what the geologic record was
telling us.
>> Demenocal had finally solved
the riddle of the sands.
The Sahara has been a desert
wasteland for 3 million years.
In the search to discover the
age of the Sahara, geologists
have unearthed two startling
clues.
Yardangs show that windblown
sand has been blasting across
the desert for at least one
million years.
Deep-sea
cores give a more exact date.
The Sahara first turned from
swamp to sand 3 million years
ago.
From that moment on, the Sahara
became the searing wasteland we
see today.
It seemed that geology alone
could explain the creation of
the world's largest desert.
Then a new radar fitted to the
space shuttle revealed a
striking clue that the desert
once harbored a slash of green
across its burning sands.
>> Booster ignition and liftoff.
>> In 1981, the space shuttle
ade a surprising discovery.
Using a new type of radar, NASA
took a 30-mile-wide
scan of the Sahara desert.
The radar pierced the sand to a
depth of 16 feet and revealed
what looked like a hidden
network of ancient waterways
crisscrossing the desert.
This find has stumped scientists.
3 million years ago, the Sahara
turned from rainforest into
desert.
Now it seemed that it had been
home to a lot of water at some
point in the following 3 million
years.
Researchers followed the NASA
images north into Tunisia, to
the edge of a deep depression in
the Sahara, the site of their
first clue.
>> This is what we're
looking for.
There's some quite intact
shells here.
This deposit is largely composed
of intact shells.
>> And these are not shells from
the ocean.
>> So, here we have half of a
cadastradurnam glorcum shell,
which is clear sign of
a freshwater lake.
This is just one example of what
must be millions of shells.
We must be somewhere near the
shoreline of a lake here.
>> Further shell deposits reveal
that this lake was giant, about
the size of West Virginia, but
the shells provide even more
remarkable evidence--the date
when this lake existed.
Carbon dating puts them at
90,000 years old and leads to
one conclusion.
>> To have all of these shells
here, we must have had a lot of
rain falling in the
vicinity of this lake and a
green Sahara.
>> Scientists fanned out across
the Sahara to investigate other
satellite images.
They searched for any dips in
its landscape that looked like
they once held a body
of fresh water.
>> So, what was really exciting
for me about those radar images
produced by NASA, we can
link this to the gps, and we're
finding evidence of lakes
throughout the desert, and some
of these lakes are massive.
>> 3 different lake locations
were confirmed by the presence
of freshwater shells.
The series of ancient lakes were
so large, they've been dubbed
Megalakes.
>> So, this is the far shore of
the megalake.
This is just one of many lakes
across the green Sahara.
>> When Drake added up the
evidence of all the lake
locations, he uncovered an
astonishing fact.
>> Ok, so if this is North
Africa here and this is the edge
of the Sahara desert--so we're
here in Tunisia with a megalake
here, and we know there's
another megalake here in
Southern Libya, an even larger
one here in Chad--if they all
reached their maximum size, they
would have covered 10% of the
Sahara.
>> That would have made them 3
times larger than the Great
Lakes.
What is now the biggest desert
on Earth was once home to some
of the planet's largest bodies
of fresh water.
Sudden changes in climate have
been connected to everything
from volcanic activity to
meteors hitting the Earth, but
climate researcher Peter
Demenocal had a hunch this
wasn't the first time it had
happened.
He turned to his archive of deep
ocean cores.
>> Our approach was to use
deep-sea
sediments as this continuous
tape recorder, if you will, of
past climate change in Africa.
>> By looking at the levels of
desert dust in cores dating back
hundreds of thousands of years,
he discovered the Sahara had
changed more than once.
>> When we first collected these
measurements, I really kind of
almost fell back in my chair
because what we saw was, there
are many switches like this in
the climate system.
>> To explain these regular
dramatic changes, Demenocal
looked beyond the Sahara to the
rotation of the Earth itself,
more specifically, small wobbles
in the Earth's orbit around the
Sun.
The theory is that the wobble
causes the Earth to tilt
slightly.
So, the monsoons which drench
Southern Africa today shift up,
pouring rain onto the dunes of
the Sahara.
Crucially, these wobbles occur
every 20,000 years.
>> So, there's this perfect
one-to-one
match between when Africa was
wet and the stage of the wobble
cycle, and this goes back
millions of years.
>> Each time the rain belt moves
up, the landscape is
transformed, and the desert
turns green.
>> To me the single most
impressive thing about the
Sahara is how small fluctuations
in something as simple as a
wobble in the Earth's orbit can
lead to these really just
totally dramatic changes
in the climate of a region
that's so large.
>> Scientists now had evidence
of how and why the Sahara turned
green.
They knew that giant lakes
covered much of the desert, but
they had no proof they were
connected.
Were these vast isolated rain
pools or part of an
interconnected river system, as
suggested by NASA's radar
images?
Nick Drake gets word that, in
2009, archaeologists have made
an important discovery that
supports the river theory--stone
tools found not far from the
site of the megalake in Tunisia.
The first step is to identify
the shoreline of the ancient
lake.
>> Ah, now, this looks good.
So, we got some freshwater
mollusks.
>> These tiny shells are a good
sign of the lake.
Now he searches for what may
have been drinking the water
when the megalake existed.
>> We have what looks like part
of a jawbone of a small
herbivore.
You can see 3 teeth running
along there.
Some sort of gazelle.
>> So, animals must have existed
here in the desert when it was
green.
>> Ok. So, we got a stone
tool here.
It's become blunted, and they've
retouched it with a lot of very
fine flakes off the edge.
The fact that we got stone
tools and we've got dead animals
suggests hunting, and this was
the animal that was being
hunted, and then we have water,
so people sitting around a water
hole waiting for animals to come
to drink and then killing them,
eating them, leaving them
behind.
>> It's an important find.
A stone-age
tool shows people lived on the
shore of this ancient lake, and
90,000 years ago was a turning
point not just in the story of
the Sahara, but in the history
of humanity itself.
We are all descended from one
group of people in East Africa,
the birthplace of humankind.
Sometime between 80,000 and
120,000 years ago, modern humans
started the long journey out of
Africa.
No one knows for certain what
route they took.
The prevailing view is that
the Sahara was impassable, so
humans left East Africa and
traveled to the coast, then
crossed a land bridge into the
Arabian peninsula, but Drake
suspects that if the megalakes
were fed by a river system, it
would have created a green
corridor across the burning
sands.
>> So, our ancestors could have
followed this river system, gone
round the lakes, followed the
next river system around the
next lake and the next river
system on the last lake, and
then they'd be in
North Africa, and it would be
simple for them to just move
out.
The lakes is good story.
The rivers plus the lake is a
very concrete story.
>> To find proof of his theory,
Drake heads to one of the few
areas in the desert where water
still flows--an oasis.
He finds a small spring that
shelters a valuable clue.
>> Caught something. Great.
A cichlid fish.
Nearly all cichlid fish are
found south of the Sahara
Desert.
This particular type of cichlid
is the only example north of the
Sahara desert.
>> This cichlid bears a strong
resemblance to its closest
relative that lives in lake
Tanganyika, but this lake is
almost 3,000 miles away on the
other side of the Sahara.
>> So, the big question is, how
did it get here?
And the most obvious answer is
that it swam across the green
Sahara.
Modern humans who could live in
lots of different types of
environments would have
presumably found it very easy,
a darn sight easier than this
fish.
>> These rivers and lakes were
not to last.
The door slammed shut on the
green corridor, but scientists
now know that the Earth's wobble
makes the Sahara like a
pendulum.
It goes from wet to dry every
20,000 years like clockwork.
The investigation has now revealed
two clues to how these wobbles
affected the Sahara.
Freshwater shells dating back
90,000 years prove the desert
was once covered by
giant, freshwater megalakes.
A cichlid fish, shows the Sahara
was crossed by a river
that created a corridor of life
across the sand.
But scientists still needed concrete
information about how rapidly
these changes occurred.
Then an Egyptian archaeologist
made a stunning discovery in the
Libyan desert--an eyewitness
account of the Sahara's last
switch, the most dramatic
climate change of the last
10,000 years.
>> Scientists piecing together
the history of the Sahara have
uncovered a remarkable story.
40 million years ago, it was
covered in ocean.
3 million years ago, the Sahara
turned to desert.
Since then, it has swung between
grassland and wasteland every
20,000 years.
Scientists now turn to the more
recent geological past, the last
10,000 years, to discover how
fast this giant desert can
change.
Investigators head to a valley
deep in the Libyan desert.
The first clue to unraveling the
mystery is a small circle of
stones.
>> This is essentially the
foundation of a hut.
It is unimaginable to see an
actual house structure right
there next to what is now
nothing.
>> Hassan's discovery is
striking evidence of human
habitation.
>> The house structure consists
of this circular foundation with
upright standing blocks which
are taken from the local
bedrock.
It would have made a
semicircular structure with
probably skins and branches, and
people would have used that as
a shelter.
>> Hassan believes these huts
could have housed a small
community of around 50 people.
Now he needs to know exactly
when they lived here.
>> Ostrich eggshell beads.
>> These little ostrich egg
beads are clearly human
handiwork.
>> They used the eggshells to
make ornamental beads cut into a
circle so a string can pass
through.
So, they string these
into bracelets or necklaces.
>> The eggshells the beads were
made from are also here and
provide the next clue.
>> The eggshells suggest, of
course, that there were
Ostriches, and that's quite
remarkable for this environment
to have animals like that.
>> This was no nomadic tribe,
but a settled farming community
rearing animals for food.
Hassan carbon-dated
the ostrich eggshell beads.
The result?
Just 7,000 years ago, the
deadliest desert on Earth was
home to both human and animal
life.
It's dramatic evidence of the
last burst of green in the
desert.
A dip in the desert floor
provides a clear sign that rain
from the monsoon fell here.
>> What we have here is
the evidence of
a deep lake with mud deposited.
>> This mud indicates a body of
water that could have supported
a settlement of people.
>> When the lake is deep, as we
can see from these layers here,
there would be a lot of
vegetation, a lot of animals,
and people would have had a very
good time.
>> At sites all across the
Sahara, scientists have
excavated similar evidence of
life--the remains of elephants
and gazelles, hippos and
crocodiles.
Remarkable cave paintings even
show people swimming.
elsewhere, human bones have been
found, carefully buried in what
were lakeside graveyards.
Analysis of these bones reveals
they date from between 10,000
and 6,000 years ago.
The question now for scientists
was how quickly the Sahara
changed from bountiful back to
bone dry.
Earlier, deep-sea
cores had provided evidence of
the moment the Sahara first
turned to desert 3 million years
ago and of how, since then, a
wobble in the Earth's axis has
made it swing like a pendulum
between desert and grassland.
Now climate researcher Peter
Demenocal is on the hunt for the
Sahara's last switch from green
to desert, one that occurred in
the last 10,000 years.
To a geologist, opening this
core is like a portal back in
time.
>> Wow, that's amazing.
It's much, much redder in the
upper part of the core.
>> Laid down flat, every
quarter-inch
of sediment in the core
represents 200 years.
The color difference in the
sediment is subtle, but to a
practiced eye, it's a big clue.
>> When we split this core, what
is surprising about it is that
we see this really impressive
color change, and it goes from
this sort of darker green-brown
color in this section of the
core, which comes from the clay
minerals that make up the deep
sea sediments.
This bright red sediment
actually comes from the
windblown dust that's coming off
the Saharan desert.
As you move along this core, you
can see this color maintains
itself further up and up into
the core.
So, right now, we're about 7,000
or 8,000 years ago.
Boom!
Here is the drying of the
Sahara.
You can put your finger on it
in this core right here--
5,500 years ago.
>> Crucially, the proximity of
these two layers reveals how
quickly the switch happened.
>> The transition from a very
well-watered,
wet Sahara that was completely
vegetated to one that was much,
much dryer, that climate
transition in this core
occurred within one or two
centuries.
>> Scientists knew that the
Sahara was an ever-changing
environment.
Now for the first time, they had
a sense of just how fast it
changed.
As the Earth wobble shifted the
rain belt away, the return to
desert was swift and deadly.
>> These transitions would have
happened almost on a
generational time scale, that
one generation after the next
after the next would have
realized that where they're
living is no longer sustainable.
>> High above the ruins of the
lake settlement, Fekri Hassan
has discovered a cave he
believes was important to the
Saharan people during this
sudden change in climate.
Perhaps it holds eyewitness
clues to what happened.
>> When I first came into the
cave, the sand was as high as
this level, and I had to crawl
in because the sand had covered
the whole area.
Well, this windblown sand cannot
form when the desert is green.
>> Buried in the sand was the
first clue--some perfectly
preserved animal droppings.
>> So, these animal droppings
not only tell us about the
climate at the time, but they
also are excellent materials for
radiocarbon dating which allow
us to date the final event of
the drying of Sahara.
>> These goat droppings covered
in sand reveal a time when a
farming community was
overwhelmed by desert.
Hidden in the back of the cave
is a clue that confirms people
sought shelter here.
>> The cave has the very
interesting feature, which is
the prints of hands.
So, this is excellent evidence
of the people that lived here.
>> The next clue suggests that
around them, the Sahara was
beginning its relentless
transformation into desert.
>> Well, here we see a very
interesting drawing with these
long lines.
This represents a cloud with
rain coming down.
Rain was becoming very scarce at
that time, and they would have
used this cave to pray for rain.
>> But with the monsoon now
several thousand miles south,
their prayers could not be
answered.
>> This cave must have been a
very important sacred place for
these people at a time when
things were getting really bad.
>> Eventually, despite these
rituals, the force of this
change was so great, they had no
choice but to leave.
>> Here in this cave, we have
the sand, and we have the
handprints, which is the last
message left by the Sahara
population.
>> The story of this cave
started with a tilt in the
Earth's axis that stopped the
rain falling on the Sahara.
What must have seemed like a
never-ending
drought would, in just 200
years, turn a gentle, fertile
region the size of the United
States into a brutal, searing
wilderness, the wasteland we see
today.
This would be the biggest
environmental upheaval of the
last 10,000 years.
Those that could must have
migrated east to their closest
source of water--the valley of
the Nile, a beacon of green in
the vast desert.
This exodus had a surprising
outcome.
The death of one culture 5,500
years ago would lead to the
birth of one of the most
advanced civilizations on the
planet.
>> It was the drying of the
desert that led to this great
civilization.
People came from different
places in the desert,
established their villages, and
within a very short time, they
began to have the basic
ingredients for the rise of
Egyptian civilization.
So, climate change in this
particular case stimulated one
of the most spectacular events
in world history.
>> The investigation into how
quickly the Sahara returns to desert
has uncovered two striking clues.
Ostrich eggshell beads show
people and animals
inhabited a green Sahara
just 7,000 years ago.
Ocean sediments
show that the Sahara
returned to desert at breakneck pace,
In just 200 hundred years.
>> The next wobble
in the Earth's axis
is set for 15,000 years from now.
Only then, will the Sahara
turn lush and green again.
But now, modern technology
is finding ways to speed up
that process.
>> The investigation into the
Sahara desert's eventful past
now moves to the last 100 years.
In 1956, French prospectors
discovered vast reserves of oil
in the Sahara.
This triggered an oil rush that
led to drilling across the
desert.
Then they struck something
unexpected under the sand--huge
quantities of fresh water.
It seemed the Sahara had another
secret to reveal.
>> So, this is a classic pumped
well drilled for irrigating the
fields, and the water is
actually pretty hot, which
means it's coming up from a
considerable depth.
>> The deeper the well, the
hotter the water.
Water from wells in the Sahara
can reach up to 150 degrees
Ffahrenheit.
Such a high temperature means
the pump is drawing water from
far enough underground to be
warmed by the Earth's internal
heat.
>> So, pumps like these can
bring up water from 3/4 of a
mile underground or even deeper.
>> With no rain for years at a
time, this water must be coming
from somewhere.
Smith spots another clue.
>> Actually, when I look at the
surroundings of the well, I can
see some orangish red iron
staining.
>> This is hematite, a mineral
that is typically found in water
that's been underground for a
long time.
Combined with the temperature,
this points to some kind of deep
reservoir.
Scientists say that,
astonishingly, great quantities
of water lie under much of the
Sahara.
The key is in the sandstone.
Sandstone is made from layers of
sand compacted into rock over
millions of years.
>> So, what's really incredible
about sandstone like this is
just how good it is at holding
water, and that's because
there's a lot of pore spaces
between the sand grains that are
actually really big.
If I pour some water on this
rock, just like would have
happened when it rained over the
Sahara, it soaks right in.
>> Scientists now know that
every 20,000 years, a wobble in
the Earth's orbit shifts the
Monsoon north so rain pours
down onto the desert.
>> Much of that rain that fell
over the Sahara is now stored
underground.
>> It's called the Nubian
Sandstone aquifer, and like a
giant subterranean sponge, it
sits below Egypt, Libya, and
Sudan.
>> Though there is nothing but
sand and rock on the surface,
under the ground beneath my feet
is as much water as there is in
the Great Lakes.
>> The presence of a reservoir,
even one deep underground, is
surprising, given the Sahara's
searingly hot temperatures.
In 1922 in neighboring Libya,
the mercury touched 136 degrees,
a record still not beaten, but
ironically, the water is
protected by the desert itself.
Layers of clay encase the
sandstone.
The clay keeps out the harsh
sun.
It also acts as a sealant,
Trapping the water within the
rocks and creating pressure.
Fault lines in this clay are the
source of the desert's famous
Oases.
>> So, this is a natural spring
where water is coming up from
the Nubian Aquifer under its own
pressure.
This is actually fossil water.
It's been dated to be up to a
million years old.
>> This reserve of water is a
legacy of the Sahara's lush,
green past, the remains of its
giant lakes and rivers, and
this is just one aquifer.
Scientists are now using
ground-penetrating
radar to locate and map other
aquifers across the Sahara.
They hold the promise of even
more fresh water.
This new technology offers hope
that the desert may once more
turn green, reclaimed for
agriculture and farming.
If all goes to plan, eventually
there will be 200 wells here,
but drilling could prove a
short-term solution.
>> This is fossil ground water.
It's not being renewed, so
eventually you're going to run
out.
Water that supported
prehistoric occupants in the
area and accumulated over a
million years is potentially
going to be gone in less than a
hundred.
>> Once the underground water
dries up, the desert will have
to wait another 15,000 years
before, once more, the Earth's
wobble turns it green again.
The mystery of what created and
changed the Sahara desert has
revealed a turbulent past.
Whale bones in the desert show
that 40 million years ago, the
Sahara was a seabed.
Deep ocean cores containing
windblown sand reveal the date
it dried up--3 million
years ago.
Freshwater shells show that
90,000 years ago, a wobble in
the Earth's axis created giant
lakes and rivers and turned the
Sahara green every 20,000 years.
Ostrich eggshell beads indicate
that just 7,000 years ago, the
Sahara enjoyed its final burst
of life before returning to
desert.
The secrets of the Sahara have
finally been revealed.
This desert is not a static
wasteland.
It's dynamic and full of life,
capable of blossoming into lush,
green terrain.
This vast, majestic land
continues to shift, change, and
evolve,
much like the Earth itself.
-- Sync, corrected by elderman -- -- for www.addic7ed.com --