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>> Earth, a unique planet,

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restless and dynamic.

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Continents shift and clash,

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volcanoes erupt.

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Glaciers grow and recede,

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titanic forces

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that are constantly at work,

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leaving a trail of geological

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mysteries behind, none greater

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than the Sahara desert--the

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hottest place on the planet, a

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deadly wasteland that time

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forgot, or so scientists

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believed till they unearthed a

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series of startling clues--the

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fossils of sea creatures,

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freshwater shells buried in

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sand, ancient settlements with

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human remains--clear evidence

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that this stark landscape hides

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a turbulent past, one that would

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alter the course of human

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history and provide a dramatic

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new chapter in the story of how

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The Earth Was Made.
S02x04 <font color=#FFFF00>Sahara</font>
Original Air Date on December 15, 2009

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-- Sync, corrected by <font color=#00FF00>elderman</font> --
-- for <font color=#00FFFF>www.addic7ed.com</font> --

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Africa's vast Sahara desert is

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as big as the United States.

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The sand alone from this giant

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expanse could bury the entire

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world 8 inches deep.

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It's the largest desert and the

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hottest place on Earth.

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>> When I first arrived in the

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Sahara, I was just struck by how

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utterly barren it was.

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It's like the color green was

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removed from the palette when

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they made this place. Just

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nothing, grays and browns and

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not a scrap of life.

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>> Smith's mission is to unearth

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evidence of what made the Sahara

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into the wasteland it is today.

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Her investigation begins on the

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desert's far eastern edge in

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Egypt, not in the sands of the

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Sahara, but in one of the most

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epic structures ever built by

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man--the great pyramids.

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The building blocks of this

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ancient wonder house a

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remarkable clue to the history

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of this land from a time long

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before the pharaohs even

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existed.

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>> So, taking a closer look at

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these blocks making up the

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Pyramids, there's actually these

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gorgeous marine fossils in here.

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Most obvious are these flat

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disks, up to about an inch wide.

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They're called nummulites, and

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they're actually single-celled

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organisms.

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>> The name nummulites means

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little coins in Latin.

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They are some of the largest

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single-celled

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creatures to have ever existed.

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In ancient times, these blocks

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were cut from quarries across

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the country and dragged to the

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pyramid site.

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Each block weighed 2 1/2 tons,

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and it took two million of them,

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and over 20 years, to build the

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Great Pyramid,

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and, incredibly, up to 40% of

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each building block is made up

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of the bodies of ancient sea

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creatures like these.

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What's even more important about

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the marine nummulites is that

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they date back 40 million years

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and they only lived in water.

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>> It's a piece of evidence that

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this area, now desert, was once

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underneath the ocean.

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You think about the

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construction of the pyramid, but

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not necessarily about what it's

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made of and these gorgeous

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fossils.

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>> The Sahara now is the world's

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biggest dustbowl, but the tiny

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nummulites fossils suggest that

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it was once very different,

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that perhaps there could have

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been water in this barren

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wilderness.

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Smith heads further inland to

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investigate this extraordinary

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idea.

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She travels to a remote desert

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valley near where the pyramid

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stones were quarried.

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It's called Wadi al Hitan.

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Spread out in the sand lie

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hundreds of fossils, first

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excavated in 1983, but these are

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nothing like the tiny

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nummulites.

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>> That's a whale.

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So, here's the backbone, the

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vertebrae.

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Here's some ribs, the shoulder,

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part of the front fin, and there

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are the jaws.

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This guy definitely did not live

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in a desert.

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>> This incredible fossil is a

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Dorudun, an ancestor of modern

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whales, one that died out 36

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million years ago.

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>> So, based on the size of

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these vertebrae and how much of

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the animal was here, it was

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probably about 21 feet long.

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This guy tells us that we were

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underwater.

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We were in the middle of an

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ocean.

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>> Wadi al Hitan is Arabic for

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Valley of the Whales.

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This 12-mile

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dip in the landscape has the

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highest concentration of fossils

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in the world.

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Some were found in the desert

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floor, others in the cliff

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walls.

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The count so far is 400.

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Almost all are marine animals,

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further evidence that the Sahara

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was once covered by sea.

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>> So, here we've got the fossil

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of a baby whale.

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You can see the lower jaw down

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here with some teeth and the

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shoulder, the backbone, some

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ribs and all curled around.

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Actually, the tail comes right

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back to near the head.

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>> As if finding whales in the

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desert wasn't intriguing enough,

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there's yet another mystery to

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be solved.

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A lot of the fossils are of very

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young dorudons, like this one.

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A delicate mesh of stone helps

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explain why so many baby whales

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died in this place.

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>> Wow, so finding that whale

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fossil told us we were in the

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ocean.

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These rocks acutally tell us a

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lot more about what type of

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ocean we were dealing with.

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These are all fossilized

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mangrove roots.

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>> These roots would have been

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below water.

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The mangrove trees would have

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risen above it.

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>> Since trees don't grow out of

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the deep ocean, we know that

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this area was actually under

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shallow ocean at the time these

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rocks were deposited, something

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probably that looked like the

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Florida Everglades, where there

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are mangroves growing now.

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>> Smith has discovered the

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shoreline of the ancient sea.

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The shallowness of the water

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could explain why there were so

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many young animals here.

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>> So, one idea--there's a bunch

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of these baby whale fossils

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found in this area, and

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this would have been a

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shallow protected bay that maybe

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the whales came just to birth

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their young.

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It is absolutely incredible to

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see a fossilized whale in a

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place that, right now, gets less

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than a millimeter of rainfall a

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year.

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It's as much convincing evidence

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for geologic change as I can

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imagine.

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>> The pieces of the puzzle are

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coming together to reveal the

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Sahara's watery past.

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>> So, 40 million years ago,

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this desert would have been

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covered in the middle of this

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valley by a shallow bay,

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probably a brilliant tropical

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blue-green color.

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The shoreline would have been

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off along the horizon, some

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mangrove trees in the shallowest

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parts of it.

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>> Inland would have been a

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vibrant combination of

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rainforest and swampland.

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The whales would have been drawn

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to this ancient shore because of

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the plentiful supply of food,

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but their ocean is about to

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vanish.

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Marine fossils found in

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Europe and Africa are evidence

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that this ocean stretched almost

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halfway around the world and

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connectedAasia to the Atlantic.

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It's called the Tethys Sea, and

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much of the Sahara was submerged

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under it.

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The mystery is how and when this

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lush water world turned into the

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barren wasteland we see today.

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The answer lies not in climate

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patterns, but in geology.

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The entire African continent

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is underpinned by a giant piece

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of the Earth's crust.

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It's called a tectonic plate,

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and 40 million years ago, in

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what is known as the Eocene Age,

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it was on the move.

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>> So, at Wadi al Hitan, we have

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whales swimming around in this

247
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Eocene Ocean.

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All the while, the African plate

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is moving to the north.

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Africa collides with Europe,

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closing the Tethys Sea, but the

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African plate keeps moving

253
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>> So we uplifted the northern

254
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part of Africa,

255
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and so the Tethys Sea recedes,

256
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and we've got this whole area of

257
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North Africa now emerged.

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It's out on land.

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>> The whales of Wadi al Hitan

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are cut off and trapped in

261
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smaller and smaller pools of

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water.

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The deadly Sahara has claimed

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its first victims.

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In the quest to discover the

266
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history of the vast Sahara

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Desert, geologists have so far

268
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uncovered two important clues.

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Sea fossils in the great

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Pyramids of Egypt show these

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building blocks were once

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underwater.

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Whale bones reveal that a sea

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submerged much of the Sahara 37

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million years ago.

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As the forces of plate tectonics

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pushed the Sahara out from under

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the sea, it created a tropical

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swamp.

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In order to figure out what made

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it into the wasteland visible

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today, scientists have to

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pinpoint the moment of its

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birth, but the clues to this

285
00:10:08,365 --> 00:10:10,099
mystery turn out to be hidden in

286
00:10:10,167 --> 00:10:13,206
the last place anyone expected.

287
00:10:17,086 --> 00:10:18,621
>> 20 million years ago, the

288
00:10:18,688 --> 00:10:19,955
Sahara desert was a lush

289
00:10:20,023 --> 00:10:22,425
tropical swamp.

290
00:10:22,492 --> 00:10:23,893
Geologists are now piecing

291
00:10:23,960 --> 00:10:25,895
together the story of the next

292
00:10:25,962 --> 00:10:28,531
20 million years.

293
00:10:28,598 --> 00:10:30,232
Today the Sahara lies in what is

294
00:10:30,333 --> 00:10:32,334
known as the desert belt, a

295
00:10:32,436 --> 00:10:34,336
region of dry air north of the

296
00:10:34,438 --> 00:10:35,971
equator.

297
00:10:36,073 --> 00:10:38,074
Here, strong winds clear the sky

298
00:10:38,175 --> 00:10:40,242
of clouds and dry out the land

299
00:10:40,310 --> 00:10:41,811
below.

300
00:10:41,878 --> 00:10:43,712
It stretches through the Gobi

301
00:10:43,780 --> 00:10:45,581
Desert in China and across the

302
00:10:45,615 --> 00:10:47,149
deserts of the southwestern

303
00:10:47,184 --> 00:10:49,452
United States.

304
00:10:49,519 --> 00:10:51,520
The Sahara is the largest, and

305
00:10:51,588 --> 00:10:52,955
yet geologists know next to

306
00:10:52,989 --> 00:10:54,457
nothing about when it was

307
00:10:54,524 --> 00:10:55,724
created.

308
00:10:55,725 --> 00:10:56,625
>> What we have are just these

309
00:10:56,726 --> 00:10:58,160
little bits and pieces, these

310
00:10:58,261 --> 00:11:00,429
snapshots of what the Sahara was

311
00:11:00,464 --> 00:11:01,897
like, because the wind blows

312
00:11:01,898 --> 00:11:03,232
away a lot of our record, and

313
00:11:03,266 --> 00:11:04,700
what isn't blown away is often

314
00:11:04,734 --> 00:11:05,968
covered by sand.

315
00:11:06,002 --> 00:11:07,169
So, it's kind of hard to find

316
00:11:07,237 --> 00:11:08,537
the rocks we need to tell the

317
00:11:08,605 --> 00:11:11,173
story we're trying to tell.

318
00:11:11,241 --> 00:11:12,441
>> One of the few places that

319
00:11:12,542 --> 00:11:14,343
shelters a clue to the Sahara's

320
00:11:14,377 --> 00:11:17,446
birth is the white desert.

321
00:11:17,514 --> 00:11:18,881
In this hauntingly beautiful

322
00:11:18,915 --> 00:11:20,916
site, dramatic shapes have been

323
00:11:21,017 --> 00:11:23,352
sculpted out of rock.

324
00:11:23,386 --> 00:11:25,788
>> Oh, this is great.

325
00:11:25,822 --> 00:11:29,892
It's got that mushroom shape.

326
00:11:29,960 --> 00:11:31,327
>> These structures are called

327
00:11:31,428 --> 00:11:33,262
Yardangs, and they are a kind of

328
00:11:33,330 --> 00:11:34,964
hourglass that could help

329
00:11:35,065 --> 00:11:37,266
measure the age of the desert.

330
00:11:37,334 --> 00:11:38,534
>> This rock is another

331
00:11:38,602 --> 00:11:39,602
piece of evidence that this

332
00:11:39,669 --> 00:11:41,537
desert was once under the ocean.

333
00:11:41,605 --> 00:11:43,072
It's actually a chalk made up of

334
00:11:43,173 --> 00:11:44,607
billions of little marine

335
00:11:44,674 --> 00:11:46,976
micro-organisms.

336
00:11:47,077 --> 00:11:48,244
These chalks are actually really

337
00:11:48,345 --> 00:11:49,612
easy to erode, so that's one

338
00:11:49,713 --> 00:11:51,147
reason things are so beautifully

339
00:11:51,181 --> 00:11:52,448
sculpted by the wind.

340
00:11:52,549 --> 00:11:53,983
>> But the wind is a brutal

341
00:11:54,084 --> 00:11:55,184
creator.

342
00:11:55,252 --> 00:11:56,886
It picks up sand and hurls it at

343
00:11:56,987 --> 00:11:58,420
the Yardang.

344
00:11:58,455 --> 00:11:59,622
>> When wind scours or

345
00:11:59,689 --> 00:12:01,223
sandblasts the rocks, this is

346
00:12:01,324 --> 00:12:02,791
the characteristic shape that we

347
00:12:02,826 --> 00:12:04,827
get, this mushroom shape,

348
00:12:04,895 --> 00:12:06,328
narrower in the middle.

349
00:12:06,363 --> 00:12:08,097
That's because the wind goes

350
00:12:08,165 --> 00:12:09,965
faster as you move up from the

351
00:12:10,000 --> 00:12:11,734
ground, so it can erode harder,

352
00:12:11,801 --> 00:12:13,102
but it has less sand in it

353
00:12:13,170 --> 00:12:14,336
since it picks up the sand from

354
00:12:14,371 --> 00:12:15,371
the ground.

355
00:12:15,438 --> 00:12:16,539
So, where we get the most

356
00:12:16,640 --> 00:12:17,740
erosion, where the rock is

357
00:12:17,807 --> 00:12:19,642
narrowest, is where we have the

358
00:12:19,709 --> 00:12:22,344
best mix of fast wind and the

359
00:12:22,379 --> 00:12:24,747
most sand.

360
00:12:24,814 --> 00:12:26,448
>> 40 million years ago, the top

361
00:12:26,550 --> 00:12:28,284
of the Yardangs formed part of

362
00:12:28,385 --> 00:12:31,453
the solid sea floor, but the

363
00:12:31,521 --> 00:12:33,355
wind picked up once the Sahara

364
00:12:33,390 --> 00:12:34,790
turned to desert, and the

365
00:12:34,824 --> 00:12:36,358
process of carving out these

366
00:12:36,459 --> 00:12:38,394
shapes began.

367
00:12:38,461 --> 00:12:40,362
Figuring out how long that took

368
00:12:40,463 --> 00:12:42,198
could help pinpoint the age of

369
00:12:42,265 --> 00:12:44,433
the desert.

370
00:12:44,467 --> 00:12:45,834
>> It's hard to say precisely

371
00:12:45,902 --> 00:12:46,936
how long it would take for the

372
00:12:47,003 --> 00:12:49,205
wind to carve this all out.

373
00:12:49,306 --> 00:12:50,739
Something like this about 15

374
00:12:50,840 --> 00:12:53,576
feet high, soft rock, you're

375
00:12:53,643 --> 00:12:55,444
looking at maybe only tens to a

376
00:12:55,478 --> 00:12:56,545
few hundreds of thousand of

377
00:12:56,580 --> 00:12:58,280
years, but to carve out the

378
00:12:58,381 --> 00:13:00,382
whole oasis depression, you've

379
00:13:00,450 --> 00:13:01,951
got to need at least a million

380
00:13:02,018 --> 00:13:04,220
years.

381
00:13:04,287 --> 00:13:05,387
>> But geologists suspect the

382
00:13:05,455 --> 00:13:07,122
Sahara is older than a million

383
00:13:07,224 --> 00:13:08,991
years.

384
00:13:09,025 --> 00:13:10,192
In their search for a more

385
00:13:10,227 --> 00:13:12,394
accurate date, they next turn to

386
00:13:12,462 --> 00:13:15,731
its most iconic feature--

387
00:13:15,799 --> 00:13:20,469
Sand dunes.

388
00:13:20,537 --> 00:13:22,171
Here in the Sahara, sandstorms

389
00:13:22,272 --> 00:13:23,739
kick up that can last for 4

390
00:13:23,807 --> 00:13:26,108
days.

391
00:13:26,176 --> 00:13:27,543
The sand is hurled across the

392
00:13:27,644 --> 00:13:29,545
terrain.

393
00:13:29,613 --> 00:13:30,646
Over hundreds of thousands of

394
00:13:30,747 --> 00:13:32,815
years, it accumulates into dunes

395
00:13:32,882 --> 00:13:36,752
that can tower 50 stories high.

396
00:13:36,820 --> 00:13:38,621
Perhaps these mountains of sand

397
00:13:38,655 --> 00:13:40,122
hold the secret of the desert's

398
00:13:40,190 --> 00:13:42,758
great age.

399
00:13:42,826 --> 00:13:43,892
>> As soon as the climate

400
00:13:43,927 --> 00:13:45,194
becomes arid, you can start

401
00:13:45,262 --> 00:13:46,562
building dunes, and if we want

402
00:13:46,630 --> 00:13:48,664
to know how long that took, we

403
00:13:48,732 --> 00:13:49,832
can try and date the dunes

404
00:13:49,899 --> 00:13:51,100
themselves, but that's really

405
00:13:51,167 --> 00:13:52,034
hard.

406
00:13:52,102 --> 00:13:53,202
>> What's hard is that these

407
00:13:53,270 --> 00:13:55,371
dunes are constantly shifting.

408
00:13:55,472 --> 00:13:56,905
The wind that builds them also

409
00:13:56,940 --> 00:13:58,941
blows them away, moving them an

410
00:13:59,009 --> 00:14:01,577
average of 50 feet a year.

411
00:14:01,678 --> 00:14:03,012
To get a precise age for the

412
00:14:03,046 --> 00:14:04,380
desert, scientists need to

413
00:14:04,447 --> 00:14:06,015
follow the sand to the end of

414
00:14:06,116 --> 00:14:07,383
its journey.

415
00:14:07,484 --> 00:14:09,485
>> Coarse sand travels slowly

416
00:14:09,586 --> 00:14:11,654
and doesn't go all that far, but

417
00:14:11,721 --> 00:14:14,189
the finer particles will

418
00:14:14,224 --> 00:14:16,292
actually travel further, and so

419
00:14:16,393 --> 00:14:18,127
dust-sized particles actually

420
00:14:18,228 --> 00:14:19,395
can get carried out into the

421
00:14:19,462 --> 00:14:21,196
Atlantic.

422
00:14:21,231 --> 00:14:22,564
>> The Sahara is the largest

423
00:14:22,599 --> 00:14:25,200
source of dust on the planet.

424
00:14:25,268 --> 00:14:27,536
500 million tons of it ends up

425
00:14:27,570 --> 00:14:30,272
in the Atlantic every year.

426
00:14:30,373 --> 00:14:31,473
Some of it reaches as far as

427
00:14:31,541 --> 00:14:33,375
Florida and creates spectacular

428
00:14:33,476 --> 00:14:37,346
red sunsets, but much of it

429
00:14:37,380 --> 00:14:39,181
settles on the ocean floor, a

430
00:14:39,249 --> 00:14:40,749
treasure trove of information

431
00:14:40,817 --> 00:14:43,952
about the Sahara's past.

432
00:14:43,987 --> 00:14:44,953
>> What's wonderful about

433
00:14:44,988 --> 00:14:45,854
working with the ocean sediments

434
00:14:45,889 --> 00:14:47,890
is that they capture everything.

435
00:14:47,891 --> 00:14:49,725
They're this very faithful

436
00:14:49,793 --> 00:14:51,694
recorder of the sediments that

437
00:14:51,795 --> 00:14:52,695
are raining down from the

438
00:14:52,762 --> 00:14:53,696
surface.

439
00:14:53,697 --> 00:14:56,198
>> In 1995, Demenocal drilled

440
00:14:56,232 --> 00:14:58,834
down into the ocean floor

441
00:14:58,868 --> 00:15:00,235
through layers of mud dating

442
00:15:00,337 --> 00:15:03,405
back millions of years.

443
00:15:03,473 --> 00:15:04,973
Each layer of sediment is like a

444
00:15:05,041 --> 00:15:06,675
time capsule.

445
00:15:06,743 --> 00:15:08,210
Shallow levels show plenty of

446
00:15:08,244 --> 00:15:09,845
this dust blown over from the

447
00:15:09,879 --> 00:15:12,247
desert.

448
00:15:12,315 --> 00:15:14,116
So, Demenocal extracted deeper

449
00:15:14,150 --> 00:15:15,851
core samples from over a million

450
00:15:15,885 --> 00:15:17,152
years ago.

451
00:15:17,253 --> 00:15:20,255
Still there was desert dust.

452
00:15:20,323 --> 00:15:22,157
Finally, he dug down to a layer

453
00:15:22,225 --> 00:15:23,892
that was laid down 3 million

454
00:15:23,960 --> 00:15:26,328
years ago, and there the dust

455
00:15:26,429 --> 00:15:28,597
finally stopped.

456
00:15:28,698 --> 00:15:29,865
It had taken a voyage to the

457
00:15:29,899 --> 00:15:31,600
ocean floor to uncover the

458
00:15:31,668 --> 00:15:33,068
turning point from humid,

459
00:15:33,169 --> 00:15:35,204
tropical landscape into searing

460
00:15:35,271 --> 00:15:37,406
desert.

461
00:15:37,507 --> 00:15:38,374
>> That's a pretty amazing

462
00:15:38,408 --> 00:15:39,274
change.

463
00:15:39,309 --> 00:15:41,210
You don't think of something as

464
00:15:41,311 --> 00:15:44,480
large and expansive and fixed as

465
00:15:44,514 --> 00:15:46,782
the Saharan desert as being

466
00:15:46,850 --> 00:15:48,851
something capable of such

467
00:15:48,918 --> 00:15:50,586
profound changes, and yet this

468
00:15:50,653 --> 00:15:51,687
is what the geologic record was

469
00:15:51,788 --> 00:15:54,022
telling us.

470
00:15:54,057 --> 00:15:56,058
>> Demenocal had finally solved

471
00:15:56,126 --> 00:15:58,060
the riddle of the sands.

472
00:15:58,128 --> 00:15:59,328
The Sahara has been a desert

473
00:15:59,429 --> 00:16:04,666
wasteland for 3 million years.

474
00:16:04,701 --> 00:16:06,201
In the search to discover the

475
00:16:06,236 --> 00:16:08,404
age of the Sahara, geologists

476
00:16:08,505 --> 00:16:09,805
have unearthed two startling

477
00:16:09,873 --> 00:16:12,141
clues.

478
00:16:12,142 --> 00:16:14,309
Yardangs show that windblown

479
00:16:14,344 --> 00:16:16,145
sand has been blasting across

480
00:16:16,212 --> 00:16:17,980
the desert for at least one

481
00:16:18,047 --> 00:16:20,048
million years.

482
00:16:20,150 --> 00:16:21,350
Deep-sea

483
00:16:21,418 --> 00:16:23,218
cores give a more exact date.

484
00:16:23,253 --> 00:16:24,787
The Sahara first turned from

485
00:16:24,888 --> 00:16:27,222
swamp to sand 3 million years

486
00:16:27,257 --> 00:16:31,527
ago.

487
00:16:31,528 --> 00:16:33,128
From that moment on, the Sahara

488
00:16:33,163 --> 00:16:34,963
became the searing wasteland we

489
00:16:35,064 --> 00:16:37,065
see today.

490
00:16:37,133 --> 00:16:38,801
It seemed that geology alone

491
00:16:38,902 --> 00:16:40,269
could explain the creation of

492
00:16:40,336 --> 00:16:43,405
the world's largest desert.

493
00:16:43,440 --> 00:16:45,541
Then a new radar fitted to the

494
00:16:45,608 --> 00:16:46,975
space shuttle revealed a

495
00:16:47,043 --> 00:16:48,710
striking clue that the desert

496
00:16:48,778 --> 00:16:50,879
once harbored a slash of green

497
00:16:50,914 --> 00:16:53,816
across its burning sands.

498
00:16:58,443 --> 00:17:03,313
>> Booster ignition and liftoff.

499
00:17:03,415 --> 00:17:05,416
>> In 1981, the space shuttle

500
00:17:05,483 --> 00:17:09,219
ade a surprising discovery.

501
00:17:09,287 --> 00:17:11,221
Using a new type of radar, NASA

502
00:17:11,322 --> 00:17:12,790
took a 30-mile-wide

503
00:17:12,857 --> 00:17:17,194
scan of the Sahara desert.

504
00:17:17,228 --> 00:17:18,796
The radar pierced the sand to a

505
00:17:18,863 --> 00:17:22,866
depth of 16 feet and revealed

506
00:17:22,967 --> 00:17:24,334
what looked like a hidden

507
00:17:24,402 --> 00:17:26,570
network of ancient waterways

508
00:17:26,604 --> 00:17:30,607
crisscrossing the desert.

509
00:17:30,708 --> 00:17:34,411
This find has stumped scientists.

510
00:17:34,512 --> 00:17:36,046
3 million years ago, the Sahara

511
00:17:36,147 --> 00:17:37,881
turned from rainforest into

512
00:17:37,949 --> 00:17:39,416
desert.

513
00:17:39,517 --> 00:17:40,784
Now it seemed that it had been

514
00:17:40,852 --> 00:17:42,886
home to a lot of water at some

515
00:17:42,954 --> 00:17:44,588
point in the following 3 million

516
00:17:44,622 --> 00:17:47,958
years.

517
00:17:47,992 --> 00:17:49,526
Researchers followed the NASA

518
00:17:49,594 --> 00:17:51,962
images north into Tunisia, to

519
00:17:51,996 --> 00:17:53,530
the edge of a deep depression in

520
00:17:53,598 --> 00:17:56,600
the Sahara, the site of their

521
00:17:56,701 --> 00:17:58,402
first clue.

522
00:17:58,436 --> 00:17:59,269
>> This is what we're

523
00:17:59,270 --> 00:18:00,704
looking for.

524
00:18:00,805 --> 00:18:02,172
There's some quite intact

525
00:18:02,273 --> 00:18:05,442
shells here.

526
00:18:05,443 --> 00:18:07,177
This deposit is largely composed

527
00:18:07,245 --> 00:18:09,446
of intact shells.

528
00:18:09,547 --> 00:18:11,148
>> And these are not shells from

529
00:18:11,182 --> 00:18:12,783
the ocean.

530
00:18:12,817 --> 00:18:14,885
>> So, here we have half of a

531
00:18:14,919 --> 00:18:16,720
cadastradurnam glorcum shell,

532
00:18:16,788 --> 00:18:18,689
which is clear sign of

533
00:18:18,723 --> 00:18:20,157
a freshwater lake.

534
00:18:20,191 --> 00:18:23,427
This is just one example of what

535
00:18:23,461 --> 00:18:26,163
must be millions of shells.

536
00:18:26,264 --> 00:18:27,164
We must be somewhere near the

537
00:18:27,265 --> 00:18:29,967
shoreline of a lake here.

538
00:18:30,001 --> 00:18:31,535
>> Further shell deposits reveal

539
00:18:31,636 --> 00:18:36,640
that this lake was giant, about

540
00:18:36,741 --> 00:18:39,543
the size of West Virginia, but

541
00:18:39,611 --> 00:18:41,445
the shells provide even more

542
00:18:41,546 --> 00:18:43,380
remarkable evidence--the date

543
00:18:43,448 --> 00:18:46,750
when this lake existed.

544
00:18:46,818 --> 00:18:48,018
Carbon dating puts them at

545
00:18:48,086 --> 00:18:50,187
90,000 years old and leads to

546
00:18:50,288 --> 00:18:52,656
one conclusion.

547
00:18:52,724 --> 00:18:53,924
>> To have all of these shells

548
00:18:53,992 --> 00:18:55,292
here, we must have had a lot of

549
00:18:55,393 --> 00:18:56,527
rain falling in the

550
00:18:56,561 --> 00:18:57,561
vicinity of this lake and a

551
00:18:57,662 --> 00:19:01,632
green Sahara.

552
00:19:01,666 --> 00:19:03,033
>> Scientists fanned out across

553
00:19:03,101 --> 00:19:05,002
the Sahara to investigate other

554
00:19:05,036 --> 00:19:07,671
satellite images.

555
00:19:07,739 --> 00:19:09,273
They searched for any dips in

556
00:19:09,307 --> 00:19:11,074
its landscape that looked like

557
00:19:11,109 --> 00:19:12,376
they once held a body

558
00:19:12,443 --> 00:19:15,112
of fresh water.

559
00:19:15,179 --> 00:19:16,179
>> So, what was really exciting

560
00:19:16,214 --> 00:19:17,447
for me about those radar images

561
00:19:17,482 --> 00:19:19,182
produced by NASA, we can

562
00:19:19,217 --> 00:19:20,817
link this to the gps, and we're

563
00:19:20,852 --> 00:19:22,019
finding evidence of lakes

564
00:19:22,120 --> 00:19:23,820
throughout the desert, and some

565
00:19:23,855 --> 00:19:26,123
of these lakes are massive.

566
00:19:26,224 --> 00:19:27,925
>> 3 different lake locations

567
00:19:28,026 --> 00:19:29,593
were confirmed by the presence

568
00:19:29,661 --> 00:19:33,230
of freshwater shells.

569
00:19:33,298 --> 00:19:34,731
The series of ancient lakes were

570
00:19:34,766 --> 00:19:37,200
so large, they've been dubbed

571
00:19:37,235 --> 00:19:39,403
Megalakes.

572
00:19:39,504 --> 00:19:40,737
>> So, this is the far shore of

573
00:19:40,772 --> 00:19:42,005
the megalake.

574
00:19:42,040 --> 00:19:43,407
This is just one of many lakes

575
00:19:43,474 --> 00:19:45,943
across the green Sahara.

576
00:19:46,010 --> 00:19:46,944
>> When Drake added up the

577
00:19:47,011 --> 00:19:48,111
evidence of all the lake

578
00:19:48,146 --> 00:19:49,846
locations, he uncovered an

579
00:19:49,948 --> 00:19:52,416
astonishing fact.

580
00:19:52,483 --> 00:19:53,684
>> Ok, so if this is North

581
00:19:53,751 --> 00:19:56,687
Africa here and this is the edge

582
00:19:56,788 --> 00:19:58,422
of the Sahara desert--so we're

583
00:19:58,489 --> 00:20:01,858
here in Tunisia with a megalake

584
00:20:01,926 --> 00:20:04,861
here, and we know there's

585
00:20:04,963 --> 00:20:06,797
another megalake here in

586
00:20:06,864 --> 00:20:09,132
Southern Libya, an even larger

587
00:20:09,200 --> 00:20:14,938
one here in Chad--if they all

588
00:20:14,973 --> 00:20:16,239
reached their maximum size, they

589
00:20:16,341 --> 00:20:17,307
would have covered 10% of the

590
00:20:17,342 --> 00:20:18,575
Sahara.

591
00:20:18,610 --> 00:20:19,776
>> That would have made them 3

592
00:20:19,877 --> 00:20:21,712
times larger than the Great

593
00:20:21,779 --> 00:20:23,313
Lakes.

594
00:20:23,348 --> 00:20:24,481
What is now the biggest desert

595
00:20:24,515 --> 00:20:26,216
on Earth was once home to some

596
00:20:26,250 --> 00:20:27,951
of the planet's largest bodies

597
00:20:27,986 --> 00:20:31,655
of fresh water.

598
00:20:31,689 --> 00:20:33,023
Sudden changes in climate have

599
00:20:33,124 --> 00:20:34,391
been connected to everything

600
00:20:34,492 --> 00:20:36,326
from volcanic activity to

601
00:20:36,394 --> 00:20:42,866
meteors hitting the Earth, but

602
00:20:42,934 --> 00:20:43,967
climate researcher Peter

603
00:20:44,035 --> 00:20:45,602
Demenocal had a hunch this

604
00:20:45,670 --> 00:20:46,937
wasn't the first time it had

605
00:20:47,005 --> 00:20:48,138
happened.

606
00:20:48,239 --> 00:20:49,806
He turned to his archive of deep

607
00:20:49,841 --> 00:20:52,342
ocean cores.

608
00:20:52,377 --> 00:20:53,543
>> Our approach was to use

609
00:20:53,645 --> 00:20:54,811
deep-sea

610
00:20:54,812 --> 00:20:57,381
sediments as this continuous

611
00:20:57,482 --> 00:20:59,650
tape recorder, if you will, of

612
00:20:59,651 --> 00:21:01,385
past climate change in Africa.

613
00:21:01,486 --> 00:21:02,619
>> By looking at the levels of

614
00:21:02,654 --> 00:21:05,022
desert dust in cores dating back

615
00:21:05,089 --> 00:21:07,290
hundreds of thousands of years,

616
00:21:07,392 --> 00:21:08,659
he discovered the Sahara had

617
00:21:08,726 --> 00:21:11,628
changed more than once.

618
00:21:11,663 --> 00:21:12,763
>> When we first collected these

619
00:21:12,830 --> 00:21:14,197
measurements, I really kind of

620
00:21:14,232 --> 00:21:15,565
almost fell back in my chair

621
00:21:15,633 --> 00:21:17,668
because what we saw was, there

622
00:21:17,735 --> 00:21:18,835
are many switches like this in

623
00:21:18,903 --> 00:21:21,204
the climate system.

624
00:21:21,272 --> 00:21:22,472
>> To explain these regular

625
00:21:22,573 --> 00:21:24,474
dramatic changes, Demenocal

626
00:21:24,542 --> 00:21:26,410
looked beyond the Sahara to the

627
00:21:26,477 --> 00:21:29,546
rotation of the Earth itself,

628
00:21:29,580 --> 00:21:31,848
more specifically, small wobbles

629
00:21:31,916 --> 00:21:33,216
in the Earth's orbit around the

630
00:21:33,317 --> 00:21:34,851
Sun.

631
00:21:34,919 --> 00:21:36,586
The theory is that the wobble

632
00:21:36,654 --> 00:21:38,221
causes the Earth to tilt

633
00:21:38,289 --> 00:21:39,322
slightly.

634
00:21:39,390 --> 00:21:41,224
So, the monsoons which drench

635
00:21:41,292 --> 00:21:43,593
Southern Africa today shift up,

636
00:21:43,661 --> 00:21:45,328
pouring rain onto the dunes of

637
00:21:45,396 --> 00:21:46,863
the Sahara.

638
00:21:46,931 --> 00:21:48,932
Crucially, these wobbles occur

639
00:21:48,966 --> 00:21:51,301
every 20,000 years.

640
00:21:51,335 --> 00:21:52,502
>> So, there's this perfect

641
00:21:52,570 --> 00:21:53,503
one-to-one

642
00:21:53,604 --> 00:21:54,604
match between when Africa was

643
00:21:54,672 --> 00:21:56,106
wet and the stage of the wobble

644
00:21:56,140 --> 00:21:57,407
cycle, and this goes back

645
00:21:57,508 --> 00:21:59,876
millions of years.

646
00:21:59,944 --> 00:22:01,378
>> Each time the rain belt moves

647
00:22:01,412 --> 00:22:03,213
up, the landscape is

648
00:22:03,281 --> 00:22:05,749
transformed, and the desert

649
00:22:05,817 --> 00:22:07,551
turns green.

650
00:22:07,585 --> 00:22:08,652
>> To me the single most

651
00:22:08,720 --> 00:22:09,753
impressive thing about the

652
00:22:09,854 --> 00:22:12,189
Sahara is how small fluctuations

653
00:22:12,290 --> 00:22:13,390
in something as simple as a

654
00:22:13,458 --> 00:22:15,726
wobble in the Earth's orbit can

655
00:22:15,760 --> 00:22:17,360
lead to these really just

656
00:22:17,395 --> 00:22:18,862
totally dramatic changes

657
00:22:18,930 --> 00:22:20,263
in the climate of a region

658
00:22:20,298 --> 00:22:22,099
that's so large.

659
00:22:22,133 --> 00:22:23,934
>> Scientists now had evidence

660
00:22:24,035 --> 00:22:26,203
of how and why the Sahara turned

661
00:22:26,304 --> 00:22:27,571
green.

662
00:22:27,638 --> 00:22:29,206
They knew that giant lakes

663
00:22:29,307 --> 00:22:30,841
covered much of the desert, but

664
00:22:30,942 --> 00:22:32,309
they had no proof they were

665
00:22:32,376 --> 00:22:33,844
connected.

666
00:22:33,945 --> 00:22:36,046
Were these vast isolated rain

667
00:22:36,114 --> 00:22:37,681
pools or part of an

668
00:22:37,749 --> 00:22:39,483
interconnected river system, as

669
00:22:39,550 --> 00:22:41,284
suggested by NASA's radar

670
00:22:41,319 --> 00:22:44,221
images?

671
00:22:44,322 --> 00:22:45,756
Nick Drake gets word that, in

672
00:22:45,823 --> 00:22:48,425
2009, archaeologists have made

673
00:22:48,493 --> 00:22:49,960
an important discovery that

674
00:22:50,027 --> 00:22:52,596
supports the river theory--stone

675
00:22:52,697 --> 00:22:54,698
tools found not far from the

676
00:22:54,766 --> 00:22:58,235
site of the megalake in Tunisia.

677
00:22:58,336 --> 00:23:00,237
The first step is to identify

678
00:23:00,338 --> 00:23:01,838
the shoreline of the ancient

679
00:23:01,873 --> 00:23:03,140
lake.

680
00:23:03,207 --> 00:23:09,412
>> Ah, now, this looks good.

681
00:23:09,480 --> 00:23:12,516
So, we got some freshwater

682
00:23:12,617 --> 00:23:14,117
mollusks.

683
00:23:14,152 --> 00:23:15,619
>> These tiny shells are a good

684
00:23:15,686 --> 00:23:17,487
sign of the lake.

685
00:23:17,522 --> 00:23:19,055
Now he searches for what may

686
00:23:19,123 --> 00:23:20,423
have been drinking the water

687
00:23:20,525 --> 00:23:22,225
when the megalake existed.

688
00:23:22,260 --> 00:23:23,527
>> We have what looks like part

689
00:23:23,594 --> 00:23:25,428
of a jawbone of a small

690
00:23:25,496 --> 00:23:26,496
herbivore.

691
00:23:26,531 --> 00:23:27,430
You can see 3 teeth running

692
00:23:27,498 --> 00:23:28,698
along there.

693
00:23:28,800 --> 00:23:30,901
Some sort of gazelle.

694
00:23:30,968 --> 00:23:32,702
>> So, animals must have existed

695
00:23:32,804 --> 00:23:34,237
here in the desert when it was

696
00:23:34,338 --> 00:23:38,675
green.

697
00:23:38,709 --> 00:23:40,076
>> Ok. So, we got a stone

698
00:23:40,178 --> 00:23:41,711
tool here.

699
00:23:41,779 --> 00:23:42,779
It's become blunted, and they've

700
00:23:42,814 --> 00:23:44,815
retouched it with a lot of very

701
00:23:44,882 --> 00:23:47,250
fine flakes off the edge.

702
00:23:47,318 --> 00:23:48,351
The fact that we got stone

703
00:23:48,419 --> 00:23:51,087
tools and we've got dead animals

704
00:23:51,155 --> 00:23:52,455
suggests hunting, and this was

705
00:23:52,523 --> 00:23:53,723
the animal that was being

706
00:23:53,791 --> 00:23:55,826
hunted, and then we have water,

707
00:23:55,893 --> 00:23:58,161
so people sitting around a water

708
00:23:58,229 --> 00:23:59,596
hole waiting for animals to come

709
00:23:59,697 --> 00:24:02,999
to drink and then killing them,

710
00:24:03,067 --> 00:24:04,100
eating them, leaving them

711
00:24:04,168 --> 00:24:07,003
behind.

712
00:24:07,071 --> 00:24:09,239
>> It's an important find.

713
00:24:09,273 --> 00:24:10,373
A stone-age

714
00:24:10,441 --> 00:24:11,741
tool shows people lived on the

715
00:24:11,809 --> 00:24:14,744
shore of this ancient lake, and

716
00:24:14,812 --> 00:24:16,980
90,000 years ago was a turning

717
00:24:17,014 --> 00:24:18,815
point not just in the story of

718
00:24:18,883 --> 00:24:20,784
the Sahara, but in the history

719
00:24:20,818 --> 00:24:25,889
of humanity itself.

720
00:24:25,923 --> 00:24:27,457
We are all descended from one

721
00:24:27,525 --> 00:24:29,926
group of people in East Africa,

722
00:24:29,994 --> 00:24:33,463
the birthplace of humankind.

723
00:24:33,564 --> 00:24:35,465
Sometime between 80,000 and

724
00:24:35,533 --> 00:24:37,934
120,000 years ago, modern humans

725
00:24:38,002 --> 00:24:39,703
started the long journey out of

726
00:24:39,737 --> 00:24:42,005
Africa.

727
00:24:42,106 --> 00:24:43,640
No one knows for certain what

728
00:24:43,741 --> 00:24:47,210
route they took.

729
00:24:47,278 --> 00:24:49,012
The prevailing view is that

730
00:24:49,080 --> 00:24:51,281
the Sahara was impassable, so

731
00:24:51,349 --> 00:24:53,216
humans left East Africa and

732
00:24:53,284 --> 00:24:54,851
traveled to the coast, then

733
00:24:54,919 --> 00:24:56,820
crossed a land bridge into the

734
00:24:56,854 --> 00:25:01,658
Arabian peninsula, but Drake

735
00:25:01,759 --> 00:25:03,827
suspects that if the megalakes

736
00:25:03,861 --> 00:25:06,196
were fed by a river system, it

737
00:25:06,264 --> 00:25:07,764
would have created a green

738
00:25:07,832 --> 00:25:10,000
corridor across the burning

739
00:25:10,034 --> 00:25:13,403
sands.

740
00:25:13,504 --> 00:25:14,771
>> So, our ancestors could have

741
00:25:14,839 --> 00:25:16,573
followed this river system, gone

742
00:25:16,641 --> 00:25:18,775
round the lakes, followed the

743
00:25:18,843 --> 00:25:20,043
next river system around the

744
00:25:20,111 --> 00:25:21,778
next lake and the next river

745
00:25:21,846 --> 00:25:23,280
system on the last lake, and

746
00:25:23,314 --> 00:25:24,281
then they'd be in

747
00:25:24,315 --> 00:25:25,382
North Africa, and it would be

748
00:25:25,416 --> 00:25:26,549
simple for them to just move

749
00:25:26,584 --> 00:25:28,051
out.

750
00:25:28,119 --> 00:25:29,286
The lakes is good story.

751
00:25:29,320 --> 00:25:30,487
The rivers plus the lake is a

752
00:25:30,554 --> 00:25:33,657
very concrete story.

753
00:25:33,691 --> 00:25:35,392
>> To find proof of his theory,

754
00:25:35,426 --> 00:25:36,760
Drake heads to one of the few

755
00:25:36,827 --> 00:25:38,595
areas in the desert where water

756
00:25:38,663 --> 00:25:43,700
still flows--an oasis.

757
00:25:43,768 --> 00:25:45,402
He finds a small spring that

758
00:25:45,503 --> 00:25:48,505
shelters a valuable clue.

759
00:25:48,606 --> 00:25:52,509
>> Caught something. Great.

760
00:25:52,576 --> 00:25:55,145
A cichlid fish.

761
00:25:55,212 --> 00:25:56,313
Nearly all cichlid fish are

762
00:25:56,414 --> 00:25:57,314
found south of the Sahara

763
00:25:57,415 --> 00:25:58,315
Desert.

764
00:25:58,349 --> 00:25:59,416
This particular type of cichlid

765
00:25:59,517 --> 00:26:01,484
is the only example north of the

766
00:26:01,519 --> 00:26:03,386
Sahara desert.

767
00:26:03,421 --> 00:26:04,688
>> This cichlid bears a strong

768
00:26:04,755 --> 00:26:06,056
resemblance to its closest

769
00:26:06,123 --> 00:26:07,891
relative that lives in lake

770
00:26:07,959 --> 00:26:13,530
Tanganyika, but this lake is

771
00:26:13,597 --> 00:26:16,232
almost 3,000 miles away on the

772
00:26:16,267 --> 00:26:20,236
other side of the Sahara.

773
00:26:20,271 --> 00:26:21,671
>> So, the big question is, how

774
00:26:21,706 --> 00:26:23,139
did it get here?

775
00:26:23,174 --> 00:26:25,508
And the most obvious answer is

776
00:26:25,543 --> 00:26:26,443
that it swam across the green

777
00:26:26,510 --> 00:26:28,078
Sahara.

778
00:26:28,179 --> 00:26:29,980
Modern humans who could live in

779
00:26:30,081 --> 00:26:30,880
lots of different types of

780
00:26:30,982 --> 00:26:31,715
environments would have

781
00:26:31,816 --> 00:26:33,083
presumably found it very easy,

782
00:26:33,184 --> 00:26:34,517
a darn sight easier than this

783
00:26:34,618 --> 00:26:39,622
fish.

784
00:26:39,690 --> 00:26:41,091
>> These rivers and lakes were

785
00:26:41,158 --> 00:26:42,826
not to last.

786
00:26:42,893 --> 00:26:44,527
The door slammed shut on the

787
00:26:44,595 --> 00:26:47,364
green corridor, but scientists

788
00:26:47,431 --> 00:26:49,265
now know that the Earth's wobble

789
00:26:49,333 --> 00:26:50,800
makes the Sahara like a

790
00:26:50,901 --> 00:26:52,002
pendulum.

791
00:26:52,103 --> 00:26:54,004
It goes from wet to dry every

792
00:26:54,071 --> 00:26:57,375
20,000 years like clockwork.

793
00:26:57,976 --> 00:26:59,976
The investigation has now revealed

794
00:26:59,977 --> 00:27:01,977
two clues to how these wobbles

795
00:27:01,978 --> 00:27:03,278
affected the Sahara.

796
00:27:05,579 --> 00:27:07,379
Freshwater shells dating back

797
00:27:07,380 --> 00:27:09,580
90,000 years prove the desert

798
00:27:09,581 --> 00:27:10,681
was once covered by

799
00:27:10,682 --> 00:27:12,882
giant, freshwater megalakes.

800
00:27:14,283 --> 00:27:16,183
A cichlid fish, shows the Sahara

801
00:27:16,184 --> 00:27:17,584
was crossed by a river

802
00:27:17,585 --> 00:27:19,785
that created a corridor of life

803
00:27:19,786 --> 00:27:20,786
across the sand.

804
00:27:23,510 --> 00:27:25,844
But scientists still needed concrete

805
00:27:25,911 --> 00:27:27,745
information about how rapidly

806
00:27:27,847 --> 00:27:30,081
these changes occurred.

807
00:27:30,116 --> 00:27:31,716
Then an Egyptian archaeologist

808
00:27:31,750 --> 00:27:33,184
made a stunning discovery in the

809
00:27:33,285 --> 00:27:35,753
Libyan desert--an eyewitness

810
00:27:35,821 --> 00:27:37,755
account of the Sahara's last

811
00:27:37,823 --> 00:27:39,557
switch, the most dramatic

812
00:27:39,658 --> 00:27:41,192
climate change of the last

813
00:27:41,293 --> 00:27:43,075
10,000 years.

814
00:27:45,972 --> 00:27:47,672
>> Scientists piecing together

815
00:27:47,707 --> 00:27:49,207
the history of the Sahara have

816
00:27:49,242 --> 00:27:52,878
uncovered a remarkable story.

817
00:27:52,979 --> 00:27:54,512
40 million years ago, it was

818
00:27:54,614 --> 00:27:56,781
covered in ocean.

819
00:27:56,849 --> 00:27:58,483
3 million years ago, the Sahara

820
00:27:58,517 --> 00:28:00,619
turned to desert.

821
00:28:00,686 --> 00:28:02,621
Since then, it has swung between

822
00:28:02,688 --> 00:28:04,623
grassland and wasteland every

823
00:28:04,690 --> 00:28:07,425
20,000 years.

824
00:28:07,493 --> 00:28:09,060
Scientists now turn to the more

825
00:28:09,128 --> 00:28:11,396
recent geological past, the last

826
00:28:11,430 --> 00:28:14,699
10,000 years, to discover how

827
00:28:14,800 --> 00:28:16,968
fast this giant desert can

828
00:28:17,069 --> 00:28:22,173
change.

829
00:28:22,241 --> 00:28:23,975
Investigators head to a valley

830
00:28:24,043 --> 00:28:28,680
deep in the Libyan desert.

831
00:28:28,714 --> 00:28:30,448
The first clue to unraveling the

832
00:28:30,516 --> 00:28:32,517
mystery is a small circle of

833
00:28:32,551 --> 00:28:34,419
stones.

834
00:28:34,453 --> 00:28:35,887
>> This is essentially the

835
00:28:35,955 --> 00:28:38,156
foundation of a hut.

836
00:28:38,157 --> 00:28:41,359
It is unimaginable to see an

837
00:28:41,427 --> 00:28:43,061
actual house structure right

838
00:28:43,095 --> 00:28:44,896
there next to what is now

839
00:28:44,997 --> 00:28:46,464
nothing.

840
00:28:46,465 --> 00:28:47,632
>> Hassan's discovery is

841
00:28:47,733 --> 00:28:49,601
striking evidence of human

842
00:28:49,635 --> 00:28:51,102
habitation.

843
00:28:51,170 --> 00:28:54,906
>> The house structure consists

844
00:28:54,974 --> 00:28:57,375
of this circular foundation with

845
00:28:57,443 --> 00:29:00,011
upright standing blocks which

846
00:29:00,079 --> 00:29:01,746
are taken from the local

847
00:29:01,814 --> 00:29:02,914
bedrock.

848
00:29:03,015 --> 00:29:05,750
It would have made a

849
00:29:05,818 --> 00:29:07,719
semicircular structure with

850
00:29:07,820 --> 00:29:09,721
probably skins and branches, and

851
00:29:09,822 --> 00:29:10,889
people would have used that as

852
00:29:10,923 --> 00:29:12,290
a shelter.

853
00:29:12,358 --> 00:29:13,658
>> Hassan believes these huts

854
00:29:13,726 --> 00:29:14,926
could have housed a small

855
00:29:15,027 --> 00:29:18,630
community of around 50 people.

856
00:29:18,664 --> 00:29:20,465
Now he needs to know exactly

857
00:29:20,533 --> 00:29:22,367
when they lived here.

858
00:29:22,435 --> 00:29:24,669
>> Ostrich eggshell beads.

859
00:29:24,737 --> 00:29:26,004
>> These little ostrich egg

860
00:29:26,072 --> 00:29:27,572
beads are clearly human

861
00:29:27,640 --> 00:29:29,207
handiwork.

862
00:29:29,275 --> 00:29:30,709
>> They used the eggshells to

863
00:29:30,743 --> 00:29:33,645
make ornamental beads cut into a

864
00:29:33,713 --> 00:29:35,847
circle so a string can pass

865
00:29:35,915 --> 00:29:36,948
through.

866
00:29:37,016 --> 00:29:38,183
So, they string these

867
00:29:38,217 --> 00:29:41,953
into bracelets or necklaces.

868
00:29:42,021 --> 00:29:43,588
>> The eggshells the beads were

869
00:29:43,656 --> 00:29:45,490
made from are also here and

870
00:29:45,558 --> 00:29:48,159
provide the next clue.

871
00:29:48,194 --> 00:29:49,828
>> The eggshells suggest, of

872
00:29:49,895 --> 00:29:50,829
course, that there were

873
00:29:50,896 --> 00:29:52,263
Ostriches, and that's quite

874
00:29:52,365 --> 00:29:54,599
remarkable for this environment

875
00:29:54,633 --> 00:29:56,701
to have animals like that.

876
00:29:56,736 --> 00:29:59,537
>> This was no nomadic tribe,

877
00:29:59,638 --> 00:30:01,272
but a settled farming community

878
00:30:01,374 --> 00:30:04,909
rearing animals for food.

879
00:30:04,977 --> 00:30:06,277
Hassan carbon-dated

880
00:30:06,379 --> 00:30:08,446
the ostrich eggshell beads.

881
00:30:08,547 --> 00:30:10,382
The result?

882
00:30:10,449 --> 00:30:12,384
Just 7,000 years ago, the

883
00:30:12,451 --> 00:30:14,919
deadliest desert on Earth was

884
00:30:15,021 --> 00:30:17,288
home to both human and animal

885
00:30:17,356 --> 00:30:18,523
life.

886
00:30:18,557 --> 00:30:20,025
It's dramatic evidence of the

887
00:30:20,092 --> 00:30:22,027
last burst of green in the

888
00:30:22,094 --> 00:30:25,030
desert.

889
00:30:25,097 --> 00:30:26,564
A dip in the desert floor

890
00:30:26,632 --> 00:30:28,566
provides a clear sign that rain

891
00:30:28,667 --> 00:30:31,102
from the monsoon fell here.

892
00:30:31,203 --> 00:30:32,871
>> What we have here is

893
00:30:32,938 --> 00:30:34,372
the evidence of

894
00:30:34,440 --> 00:30:37,108
a deep lake with mud deposited.

895
00:30:37,209 --> 00:30:38,743
>> This mud indicates a body of

896
00:30:38,844 --> 00:30:40,278
water that could have supported

897
00:30:40,312 --> 00:30:43,014
a settlement of people.

898
00:30:43,115 --> 00:30:45,683
>> When the lake is deep, as we

899
00:30:45,751 --> 00:30:47,919
can see from these layers here,

900
00:30:47,953 --> 00:30:48,953
there would be a lot of

901
00:30:49,021 --> 00:30:50,155
vegetation, a lot of animals,

902
00:30:50,222 --> 00:30:51,756
and people would have had a very

903
00:30:51,824 --> 00:30:54,225
good time.

904
00:30:54,293 --> 00:30:56,027
>> At sites all across the

905
00:30:56,128 --> 00:30:58,029
Sahara, scientists have

906
00:30:58,097 --> 00:30:59,831
excavated similar evidence of

907
00:30:59,865 --> 00:31:02,734
life--the remains of elephants

908
00:31:02,768 --> 00:31:05,770
and gazelles, hippos and

909
00:31:05,871 --> 00:31:08,139
crocodiles.

910
00:31:08,207 --> 00:31:09,674
Remarkable cave paintings even

911
00:31:09,742 --> 00:31:13,878
show people swimming.

912
00:31:13,946 --> 00:31:16,047
elsewhere, human bones have been

913
00:31:16,115 --> 00:31:18,216
found, carefully buried in what

914
00:31:18,317 --> 00:31:22,387
were lakeside graveyards.

915
00:31:22,421 --> 00:31:24,422
Analysis of these bones reveals

916
00:31:24,490 --> 00:31:26,691
they date from between 10,000

917
00:31:26,792 --> 00:31:31,229
and 6,000 years ago.

918
00:31:31,330 --> 00:31:33,231
The question now for scientists

919
00:31:33,332 --> 00:31:34,699
was how quickly the Sahara

920
00:31:34,767 --> 00:31:36,868
changed from bountiful back to

921
00:31:36,936 --> 00:31:40,205
bone dry.

922
00:31:40,239 --> 00:31:41,573
Earlier, deep-sea

923
00:31:41,607 --> 00:31:43,308
cores had provided evidence of

924
00:31:43,342 --> 00:31:44,876
the moment the Sahara first

925
00:31:44,977 --> 00:31:46,878
turned to desert 3 million years

926
00:31:46,946 --> 00:31:50,248
ago and of how, since then, a

927
00:31:50,349 --> 00:31:51,883
wobble in the Earth's axis has

928
00:31:51,951 --> 00:31:53,718
made it swing like a pendulum

929
00:31:53,786 --> 00:31:58,890
between desert and grassland.

930
00:31:58,991 --> 00:32:00,792
Now climate researcher Peter

931
00:32:00,893 --> 00:32:02,527
Demenocal is on the hunt for the

932
00:32:02,595 --> 00:32:04,996
Sahara's last switch from green

933
00:32:05,064 --> 00:32:07,699
to desert, one that occurred in

934
00:32:07,766 --> 00:32:10,902
the last 10,000 years.

935
00:32:10,970 --> 00:32:12,604
To a geologist, opening this

936
00:32:12,638 --> 00:32:14,439
core is like a portal back in

937
00:32:14,507 --> 00:32:16,441
time.

938
00:32:16,542 --> 00:32:17,809
>> Wow, that's amazing.

939
00:32:17,910 --> 00:32:19,144
It's much, much redder in the

940
00:32:19,178 --> 00:32:20,979
upper part of the core.

941
00:32:21,046 --> 00:32:22,247
>> Laid down flat, every

942
00:32:22,281 --> 00:32:23,414
quarter-inch

943
00:32:23,449 --> 00:32:24,549
of sediment in the core

944
00:32:24,617 --> 00:32:28,319
represents 200 years.

945
00:32:28,354 --> 00:32:29,354
The color difference in the

946
00:32:29,421 --> 00:32:30,989
sediment is subtle, but to a

947
00:32:31,056 --> 00:32:33,992
practiced eye, it's a big clue.

948
00:32:33,993 --> 00:32:35,093
>> When we split this core, what

949
00:32:35,194 --> 00:32:36,895
is surprising about it is that

950
00:32:36,962 --> 00:32:38,563
we see this really impressive

951
00:32:38,631 --> 00:32:40,965
color change, and it goes from

952
00:32:40,966 --> 00:32:42,734
this sort of darker green-brown

953
00:32:42,835 --> 00:32:44,068
color in this section of the

954
00:32:44,103 --> 00:32:45,603
core, which comes from the clay

955
00:32:45,638 --> 00:32:46,971
minerals that make up the deep

956
00:32:47,006 --> 00:32:48,106
sea sediments.

957
00:32:48,174 --> 00:32:49,107
This bright red sediment

958
00:32:49,175 --> 00:32:50,642
actually comes from the

959
00:32:50,743 --> 00:32:52,477
windblown dust that's coming off

960
00:32:52,545 --> 00:32:54,479
the Saharan desert.

961
00:32:54,547 --> 00:32:55,947
As you move along this core, you

962
00:32:56,015 --> 00:32:57,448
can see this color maintains

963
00:32:57,550 --> 00:32:59,751
itself further up and up into

964
00:32:59,818 --> 00:33:00,919
the core.

965
00:33:00,986 --> 00:33:02,287
So, right now, we're about 7,000

966
00:33:02,388 --> 00:33:03,755
or 8,000 years ago.

967
00:33:03,822 --> 00:33:04,756
Boom!

968
00:33:04,823 --> 00:33:05,723
Here is the drying of the

969
00:33:05,791 --> 00:33:06,624
Sahara.

970
00:33:06,725 --> 00:33:07,725
You can put your finger on it

971
00:33:07,793 --> 00:33:09,060
in this core right here--

972
00:33:09,094 --> 00:33:10,695
5,500 years ago.

973
00:33:10,729 --> 00:33:11,896
>> Crucially, the proximity of

974
00:33:11,964 --> 00:33:13,865
these two layers reveals how

975
00:33:13,899 --> 00:33:16,367
quickly the switch happened.

976
00:33:16,435 --> 00:33:18,069
>> The transition from a very

977
00:33:18,170 --> 00:33:19,437
well-watered,

978
00:33:19,538 --> 00:33:20,805
wet Sahara that was completely

979
00:33:20,873 --> 00:33:22,607
vegetated to one that was much,

980
00:33:22,641 --> 00:33:24,275
much dryer, that climate

981
00:33:24,343 --> 00:33:25,810
transition in this core

982
00:33:25,911 --> 00:33:27,078
occurred within one or two

983
00:33:27,179 --> 00:33:29,347
centuries.

984
00:33:29,415 --> 00:33:30,715
>> Scientists knew that the

985
00:33:30,816 --> 00:33:32,283
Sahara was an ever-changing

986
00:33:32,351 --> 00:33:33,551
environment.

987
00:33:33,619 --> 00:33:35,353
Now for the first time, they had

988
00:33:35,454 --> 00:33:37,422
a sense of just how fast it

989
00:33:37,456 --> 00:33:38,990
changed.

990
00:33:39,091 --> 00:33:40,425
As the Earth wobble shifted the

991
00:33:40,459 --> 00:33:42,260
rain belt away, the return to

992
00:33:42,294 --> 00:33:46,631
desert was swift and deadly.

993
00:33:46,665 --> 00:33:47,699
>> These transitions would have

994
00:33:47,733 --> 00:33:48,600
happened almost on a

995
00:33:48,701 --> 00:33:50,802
generational time scale, that

996
00:33:50,869 --> 00:33:52,170
one generation after the next

997
00:33:52,238 --> 00:33:52,971
after the next would have

998
00:33:53,072 --> 00:33:53,972
realized that where they're

999
00:33:54,039 --> 00:33:56,874
living is no longer sustainable.

1000
00:33:56,942 --> 00:33:58,443
>> High above the ruins of the

1001
00:33:58,510 --> 00:34:00,445
lake settlement, Fekri Hassan

1002
00:34:00,512 --> 00:34:02,080
has discovered a cave he

1003
00:34:02,147 --> 00:34:03,881
believes was important to the

1004
00:34:03,949 --> 00:34:05,416
Saharan people during this

1005
00:34:05,451 --> 00:34:08,519
sudden change in climate.

1006
00:34:08,621 --> 00:34:10,221
Perhaps it holds eyewitness

1007
00:34:10,256 --> 00:34:12,991
clues to what happened.

1008
00:34:13,058 --> 00:34:15,627
>> When I first came into the

1009
00:34:15,694 --> 00:34:18,963
cave, the sand was as high as

1010
00:34:18,998 --> 00:34:20,531
this level, and I had to crawl

1011
00:34:20,599 --> 00:34:22,066
in because the sand had covered

1012
00:34:22,167 --> 00:34:24,068
the whole area.

1013
00:34:24,103 --> 00:34:26,904
Well, this windblown sand cannot

1014
00:34:27,006 --> 00:34:30,541
form when the desert is green.

1015
00:34:30,643 --> 00:34:31,809
>> Buried in the sand was the

1016
00:34:31,910 --> 00:34:33,911
first clue--some perfectly

1017
00:34:34,013 --> 00:34:38,650
preserved animal droppings.

1018
00:34:38,717 --> 00:34:39,984
>> So, these animal droppings

1019
00:34:40,085 --> 00:34:41,152
not only tell us about the

1020
00:34:41,186 --> 00:34:43,254
climate at the time, but they

1021
00:34:43,289 --> 00:34:46,090
also are excellent materials for

1022
00:34:46,191 --> 00:34:47,625
radiocarbon dating which allow

1023
00:34:47,726 --> 00:34:50,428
us to date the final event of

1024
00:34:50,462 --> 00:34:51,729
the drying of Sahara.

1025
00:34:51,830 --> 00:34:53,364
>> These goat droppings covered

1026
00:34:53,465 --> 00:34:55,566
in sand reveal a time when a

1027
00:34:55,634 --> 00:34:56,834
farming community was

1028
00:34:56,935 --> 00:35:01,572
overwhelmed by desert.

1029
00:35:01,640 --> 00:35:03,107
Hidden in the back of the cave

1030
00:35:03,175 --> 00:35:05,209
is a clue that confirms people

1031
00:35:05,277 --> 00:35:07,011
sought shelter here.

1032
00:35:07,079 --> 00:35:08,646
>> The cave has the very

1033
00:35:08,747 --> 00:35:10,114
interesting feature, which is

1034
00:35:10,215 --> 00:35:14,652
the prints of hands.

1035
00:35:14,753 --> 00:35:17,855
So, this is excellent evidence

1036
00:35:17,923 --> 00:35:22,293
of the people that lived here.

1037
00:35:22,361 --> 00:35:24,829
>> The next clue suggests that

1038
00:35:24,930 --> 00:35:26,564
around them, the Sahara was

1039
00:35:26,632 --> 00:35:27,732
beginning its relentless

1040
00:35:27,766 --> 00:35:30,668
transformation into desert.

1041
00:35:30,736 --> 00:35:32,036
>> Well, here we see a very

1042
00:35:32,137 --> 00:35:34,005
interesting drawing with these

1043
00:35:34,039 --> 00:35:37,642
long lines.

1044
00:35:37,676 --> 00:35:41,212
This represents a cloud with

1045
00:35:41,280 --> 00:35:43,581
rain coming down.

1046
00:35:43,682 --> 00:35:46,184
Rain was becoming very scarce at

1047
00:35:46,218 --> 00:35:48,052
that time, and they would have

1048
00:35:48,120 --> 00:35:51,589
used this cave to pray for rain.

1049
00:35:51,657 --> 00:35:52,690
>> But with the monsoon now

1050
00:35:52,758 --> 00:35:54,759
several thousand miles south,

1051
00:35:54,860 --> 00:35:56,327
their prayers could not be

1052
00:35:56,395 --> 00:35:59,697
answered.

1053
00:35:59,765 --> 00:36:01,766
>> This cave must have been a

1054
00:36:01,867 --> 00:36:03,601
very important sacred place for

1055
00:36:03,669 --> 00:36:06,504
these people at a time when

1056
00:36:06,572 --> 00:36:08,573
things were getting really bad.

1057
00:36:08,607 --> 00:36:10,108
>> Eventually, despite these

1058
00:36:10,142 --> 00:36:11,976
rituals, the force of this

1059
00:36:12,044 --> 00:36:14,045
change was so great, they had no

1060
00:36:14,146 --> 00:36:17,782
choice but to leave.

1061
00:36:17,850 --> 00:36:19,951
>> Here in this cave, we have

1062
00:36:20,052 --> 00:36:22,053
the sand, and we have the

1063
00:36:22,121 --> 00:36:23,588
handprints, which is the last

1064
00:36:23,689 --> 00:36:26,157
message left by the Sahara

1065
00:36:26,258 --> 00:36:28,659
population.

1066
00:36:28,694 --> 00:36:30,595
>> The story of this cave

1067
00:36:30,696 --> 00:36:31,763
started with a tilt in the

1068
00:36:31,797 --> 00:36:33,865
Earth's axis that stopped the

1069
00:36:33,899 --> 00:36:36,868
rain falling on the Sahara.

1070
00:36:36,969 --> 00:36:37,969
What must have seemed like a

1071
00:36:38,070 --> 00:36:39,170
never-ending

1072
00:36:39,238 --> 00:36:40,905
drought would, in just 200

1073
00:36:40,973 --> 00:36:42,807
years, turn a gentle, fertile

1074
00:36:42,875 --> 00:36:44,776
region the size of the United

1075
00:36:44,810 --> 00:36:47,712
States into a brutal, searing

1076
00:36:47,780 --> 00:36:50,715
wilderness, the wasteland we see

1077
00:36:50,783 --> 00:36:53,785
today.

1078
00:36:53,819 --> 00:36:55,153
This would be the biggest

1079
00:36:55,254 --> 00:36:56,788
environmental upheaval of the

1080
00:36:56,889 --> 00:37:00,725
last 10,000 years.

1081
00:37:00,793 --> 00:37:01,993
Those that could must have

1082
00:37:02,060 --> 00:37:03,528
migrated east to their closest

1083
00:37:03,595 --> 00:37:05,263
source of water--the valley of

1084
00:37:05,330 --> 00:37:07,799
the Nile, a beacon of green in

1085
00:37:07,900 --> 00:37:11,736
the vast desert.

1086
00:37:11,804 --> 00:37:13,638
This exodus had a surprising

1087
00:37:13,739 --> 00:37:15,273
outcome.

1088
00:37:15,374 --> 00:37:17,074
The death of one culture 5,500

1089
00:37:17,142 --> 00:37:19,610
years ago would lead to the

1090
00:37:19,645 --> 00:37:21,345
birth of one of the most

1091
00:37:21,380 --> 00:37:23,281
advanced civilizations on the

1092
00:37:23,348 --> 00:37:25,716
planet.

1093
00:37:25,784 --> 00:37:27,452
>> It was the drying of the

1094
00:37:27,553 --> 00:37:28,986
desert that led to this great

1095
00:37:29,021 --> 00:37:31,189
civilization.

1096
00:37:31,256 --> 00:37:33,291
People came from different

1097
00:37:33,358 --> 00:37:34,459
places in the desert,

1098
00:37:34,560 --> 00:37:36,194
established their villages, and

1099
00:37:36,295 --> 00:37:38,362
within a very short time, they

1100
00:37:38,464 --> 00:37:39,664
began to have the basic

1101
00:37:39,731 --> 00:37:40,898
ingredients for the rise of

1102
00:37:40,999 --> 00:37:43,568
Egyptian civilization.

1103
00:37:43,635 --> 00:37:45,369
So, climate change in this

1104
00:37:45,437 --> 00:37:49,207
particular case stimulated one

1105
00:37:49,274 --> 00:37:50,842
of the most spectacular events

1106
00:37:50,909 --> 00:37:52,163
in world history.

1107
00:37:53,164 --> 00:37:54,764
>> The investigation into how

1108
00:37:54,865 --> 00:37:57,065
quickly the Sahara returns to desert

1109
00:37:57,166 --> 00:37:59,266
has uncovered two striking clues.

1110
00:38:00,867 --> 00:38:02,667
Ostrich eggshell beads show

1111
00:38:02,768 --> 00:38:04,168
people and animals

1112
00:38:04,269 --> 00:38:05,769
inhabited a green Sahara

1113
00:38:06,070 --> 00:38:08,370
just 7,000 years ago.

1114
00:38:09,571 --> 00:38:10,771
Ocean sediments

1115
00:38:10,872 --> 00:38:11,672
show that the Sahara

1116
00:38:11,773 --> 00:38:14,173
returned to desert at breakneck pace,

1117
00:38:14,274 --> 00:38:16,374
In just 200 hundred years.

1118
00:38:17,575 --> 00:38:18,475
>> The next wobble

1119
00:38:18,576 --> 00:38:19,576
in the Earth's axis

1120
00:38:19,677 --> 00:38:22,377
is set for 15,000 years from now.

1121
00:38:23,178 --> 00:38:24,778
Only then, will the Sahara

1122
00:38:24,879 --> 00:38:26,679
turn lush and green again.

1123
00:38:26,780 --> 00:38:28,880
But now, modern technology

1124
00:38:28,981 --> 00:38:31,181
is finding ways to speed up

1125
00:38:31,282 --> 00:38:32,582
that process.

1126
00:38:34,643 --> 00:38:35,576
>> The investigation into the

1127
00:38:35,677 --> 00:38:37,645
Sahara desert's eventful past

1128
00:38:37,679 --> 00:38:43,184
now moves to the last 100 years.

1129
00:38:43,251 --> 00:38:46,554
In 1956, French prospectors

1130
00:38:46,621 --> 00:38:48,722
discovered vast reserves of oil

1131
00:38:48,790 --> 00:38:50,691
in the Sahara.

1132
00:38:50,725 --> 00:38:52,359
This triggered an oil rush that

1133
00:38:52,460 --> 00:38:53,928
led to drilling across the

1134
00:38:53,995 --> 00:38:55,729
desert.

1135
00:38:55,831 --> 00:38:57,364
Then they struck something

1136
00:38:57,432 --> 00:39:00,367
unexpected under the sand--huge

1137
00:39:00,468 --> 00:39:03,370
quantities of fresh water.

1138
00:39:03,471 --> 00:39:05,272
It seemed the Sahara had another

1139
00:39:05,340 --> 00:39:10,277
secret to reveal.

1140
00:39:10,278 --> 00:39:12,479
>> So, this is a classic pumped

1141
00:39:12,547 --> 00:39:14,114
well drilled for irrigating the

1142
00:39:14,182 --> 00:39:15,549
fields, and the water is

1143
00:39:15,550 --> 00:39:16,917
actually pretty hot, which

1144
00:39:17,018 --> 00:39:18,252
means it's coming up from a

1145
00:39:18,286 --> 00:39:21,121
considerable depth.

1146
00:39:21,189 --> 00:39:22,489
>> The deeper the well, the

1147
00:39:22,557 --> 00:39:24,758
hotter the water.

1148
00:39:24,826 --> 00:39:26,193
Water from wells in the Sahara

1149
00:39:26,261 --> 00:39:28,295
can reach up to 150 degrees

1150
00:39:28,363 --> 00:39:30,564
Ffahrenheit.

1151
00:39:30,665 --> 00:39:31,899
Such a high temperature means

1152
00:39:31,933 --> 00:39:33,667
the pump is drawing water from

1153
00:39:33,768 --> 00:39:35,269
far enough underground to be

1154
00:39:35,303 --> 00:39:37,171
warmed by the Earth's internal

1155
00:39:37,205 --> 00:39:39,273
heat.

1156
00:39:39,307 --> 00:39:41,208
>> So, pumps like these can

1157
00:39:41,276 --> 00:39:43,210
bring up water from 3/4 of a

1158
00:39:43,278 --> 00:39:45,946
mile underground or even deeper.

1159
00:39:46,047 --> 00:39:47,381
>> With no rain for years at a

1160
00:39:47,415 --> 00:39:49,583
time, this water must be coming

1161
00:39:49,651 --> 00:39:51,752
from somewhere.

1162
00:39:51,820 --> 00:39:55,122
Smith spots another clue.

1163
00:39:55,190 --> 00:39:56,223
>> Actually, when I look at the

1164
00:39:56,324 --> 00:39:57,458
surroundings of the well, I can

1165
00:39:57,492 --> 00:39:58,859
see some orangish red iron

1166
00:39:58,927 --> 00:40:01,028
staining.

1167
00:40:01,096 --> 00:40:02,763
>> This is hematite, a mineral

1168
00:40:02,831 --> 00:40:04,398
that is typically found in water

1169
00:40:04,466 --> 00:40:05,833
that's been underground for a

1170
00:40:05,867 --> 00:40:07,735
long time.

1171
00:40:07,769 --> 00:40:09,203
Combined with the temperature,

1172
00:40:09,237 --> 00:40:10,871
this points to some kind of deep

1173
00:40:10,939 --> 00:40:13,140
reservoir.

1174
00:40:13,208 --> 00:40:14,508
Scientists say that,

1175
00:40:14,576 --> 00:40:16,310
astonishingly, great quantities

1176
00:40:16,411 --> 00:40:18,145
of water lie under much of the

1177
00:40:18,213 --> 00:40:19,813
Sahara.

1178
00:40:19,848 --> 00:40:23,651
The key is in the sandstone.

1179
00:40:23,685 --> 00:40:25,352
Sandstone is made from layers of

1180
00:40:25,420 --> 00:40:27,454
sand compacted into rock over

1181
00:40:27,522 --> 00:40:31,358
millions of years.

1182
00:40:31,426 --> 00:40:32,626
>> So, what's really incredible

1183
00:40:32,694 --> 00:40:34,094
about sandstone like this is

1184
00:40:34,162 --> 00:40:35,729
just how good it is at holding

1185
00:40:35,797 --> 00:40:37,231
water, and that's because

1186
00:40:37,265 --> 00:40:38,599
there's a lot of pore spaces

1187
00:40:38,633 --> 00:40:40,100
between the sand grains that are

1188
00:40:40,168 --> 00:40:43,070
actually really big.

1189
00:40:43,104 --> 00:40:44,972
If I pour some water on this

1190
00:40:45,006 --> 00:40:47,508
rock, just like would have

1191
00:40:47,542 --> 00:40:48,742
happened when it rained over the

1192
00:40:48,810 --> 00:40:54,348
Sahara, it soaks right in.

1193
00:40:54,382 --> 00:40:56,083
>> Scientists now know that

1194
00:40:56,151 --> 00:40:58,285
every 20,000 years, a wobble in

1195
00:40:58,353 --> 00:40:59,787
the Earth's orbit shifts the

1196
00:40:59,821 --> 00:41:02,189
Monsoon north so rain pours

1197
00:41:02,290 --> 00:41:04,725
down onto the desert.

1198
00:41:04,826 --> 00:41:06,093
>> Much of that rain that fell

1199
00:41:06,161 --> 00:41:07,795
over the Sahara is now stored

1200
00:41:07,829 --> 00:41:09,730
underground.

1201
00:41:09,831 --> 00:41:10,898
>> It's called the Nubian

1202
00:41:10,932 --> 00:41:12,833
Sandstone aquifer, and like a

1203
00:41:12,934 --> 00:41:15,202
giant subterranean sponge, it

1204
00:41:15,270 --> 00:41:17,304
sits below Egypt, Libya, and

1205
00:41:17,372 --> 00:41:20,574
Sudan.

1206
00:41:20,642 --> 00:41:21,742
>> Though there is nothing but

1207
00:41:21,843 --> 00:41:23,277
sand and rock on the surface,

1208
00:41:23,311 --> 00:41:25,012
under the ground beneath my feet

1209
00:41:25,113 --> 00:41:26,747
is as much water as there is in

1210
00:41:26,848 --> 00:41:29,383
the Great Lakes.

1211
00:41:29,484 --> 00:41:31,118
>> The presence of a reservoir,

1212
00:41:31,219 --> 00:41:32,953
even one deep underground, is

1213
00:41:33,021 --> 00:41:34,655
surprising, given the Sahara's

1214
00:41:34,723 --> 00:41:38,225
searingly hot temperatures.

1215
00:41:38,293 --> 00:41:41,729
In 1922 in neighboring Libya,

1216
00:41:41,763 --> 00:41:45,366
the mercury touched 136 degrees,

1217
00:41:45,400 --> 00:41:48,836
a record still not beaten, but

1218
00:41:48,870 --> 00:41:50,404
ironically, the water is

1219
00:41:50,472 --> 00:41:54,208
protected by the desert itself.

1220
00:41:54,309 --> 00:41:56,410
Layers of clay encase the

1221
00:41:56,478 --> 00:41:57,845
sandstone.

1222
00:41:57,912 --> 00:41:59,513
The clay keeps out the harsh

1223
00:41:59,581 --> 00:42:01,115
sun.

1224
00:42:01,216 --> 00:42:03,317
It also acts as a sealant,

1225
00:42:03,418 --> 00:42:04,551
Trapping the water within the

1226
00:42:04,586 --> 00:42:07,955
rocks and creating pressure.

1227
00:42:08,056 --> 00:42:09,490
Fault lines in this clay are the

1228
00:42:09,557 --> 00:42:11,425
source of the desert's famous

1229
00:42:11,493 --> 00:42:17,031
Oases.

1230
00:42:17,065 --> 00:42:19,433
>> So, this is a natural spring

1231
00:42:19,501 --> 00:42:21,135
where water is coming up from

1232
00:42:21,136 --> 00:42:22,436
the Nubian Aquifer under its own

1233
00:42:22,470 --> 00:42:23,570
pressure.

1234
00:42:23,671 --> 00:42:25,205
This is actually fossil water.

1235
00:42:25,306 --> 00:42:26,473
It's been dated to be up to a

1236
00:42:26,541 --> 00:42:29,543
million years old.

1237
00:42:29,577 --> 00:42:31,011
>> This reserve of water is a

1238
00:42:31,079 --> 00:42:32,746
legacy of the Sahara's lush,

1239
00:42:32,814 --> 00:42:35,315
green past, the remains of its

1240
00:42:35,383 --> 00:42:39,386
giant lakes and rivers, and

1241
00:42:39,454 --> 00:42:43,590
this is just one aquifer.

1242
00:42:43,658 --> 00:42:44,858
Scientists are now using

1243
00:42:44,926 --> 00:42:46,193
ground-penetrating

1244
00:42:46,227 --> 00:42:48,362
radar to locate and map other

1245
00:42:48,396 --> 00:42:50,998
aquifers across the Sahara.

1246
00:42:51,066 --> 00:42:52,466
They hold the promise of even

1247
00:42:52,534 --> 00:42:56,203
more fresh water.

1248
00:42:56,271 --> 00:42:58,172
This new technology offers hope

1249
00:42:58,206 --> 00:42:59,640
that the desert may once more

1250
00:42:59,741 --> 00:43:02,076
turn green, reclaimed for

1251
00:43:02,110 --> 00:43:04,645
agriculture and farming.

1252
00:43:04,712 --> 00:43:06,380
If all goes to plan, eventually

1253
00:43:06,481 --> 00:43:09,183
there will be 200 wells here,

1254
00:43:09,250 --> 00:43:10,751
but drilling could prove a

1255
00:43:10,819 --> 00:43:13,654
short-term solution.

1256
00:43:13,721 --> 00:43:15,055
>> This is fossil ground water.

1257
00:43:15,123 --> 00:43:16,757
It's not being renewed, so

1258
00:43:16,825 --> 00:43:18,092
eventually you're going to run

1259
00:43:18,126 --> 00:43:19,293
out.

1260
00:43:19,394 --> 00:43:20,661
Water that supported

1261
00:43:20,762 --> 00:43:21,929
prehistoric occupants in the

1262
00:43:21,996 --> 00:43:23,664
area and accumulated over a

1263
00:43:23,765 --> 00:43:25,365
million years is potentially

1264
00:43:25,400 --> 00:43:26,834
going to be gone in less than a

1265
00:43:26,935 --> 00:43:30,404
hundred.

1266
00:43:30,472 --> 00:43:31,672
>> Once the underground water

1267
00:43:31,739 --> 00:43:33,540
dries up, the desert will have

1268
00:43:33,575 --> 00:43:36,210
to wait another 15,000 years

1269
00:43:36,277 --> 00:43:38,112
before, once more, the Earth's

1270
00:43:38,179 --> 00:43:43,217
wobble turns it green again.

1271
00:43:43,284 --> 00:43:44,685
The mystery of what created and

1272
00:43:44,752 --> 00:43:46,553
changed the Sahara desert has

1273
00:43:46,588 --> 00:43:50,324
revealed a turbulent past.

1274
00:43:50,325 --> 00:43:52,226
Whale bones in the desert show

1275
00:43:52,293 --> 00:43:54,128
that 40 million years ago, the

1276
00:43:54,229 --> 00:43:57,030
Sahara was a seabed.

1277
00:43:57,132 --> 00:43:58,832
Deep ocean cores containing

1278
00:43:58,867 --> 00:44:00,467
windblown sand reveal the date

1279
00:44:00,502 --> 00:44:02,870
it dried up--3 million

1280
00:44:02,937 --> 00:44:05,005
years ago.

1281
00:44:05,039 --> 00:44:06,473
Freshwater shells show that

1282
00:44:06,508 --> 00:44:08,775
90,000 years ago, a wobble in

1283
00:44:08,877 --> 00:44:10,777
the Earth's axis created giant

1284
00:44:10,845 --> 00:44:12,679
lakes and rivers and turned the

1285
00:44:12,780 --> 00:44:17,017
Sahara green every 20,000 years.

1286
00:44:17,051 --> 00:44:19,520
Ostrich eggshell beads indicate

1287
00:44:19,587 --> 00:44:22,022
that just 7,000 years ago, the

1288
00:44:22,056 --> 00:44:24,124
Sahara enjoyed its final burst

1289
00:44:24,159 --> 00:44:26,293
of life before returning to

1290
00:44:26,361 --> 00:44:28,395
desert.

1291
00:44:28,396 --> 00:44:29,897
The secrets of the Sahara have

1292
00:44:29,931 --> 00:44:31,732
finally been revealed.

1293
00:44:31,733 --> 00:44:33,834
This desert is not a static

1294
00:44:33,935 --> 00:44:35,035
wasteland.

1295
00:44:35,103 --> 00:44:37,404
It's dynamic and full of life,

1296
00:44:37,472 --> 00:44:39,039
capable of blossoming into lush,

1297
00:44:39,107 --> 00:44:41,108
green terrain.

1298
00:44:41,209 --> 00:44:42,943
This vast, majestic land

1299
00:44:43,044 --> 00:44:45,312
continues to shift, change, and

1300
00:44:45,313 --> 00:44:46,313
evolve,

1301
00:44:47,114 --> 00:44:49,114
much like the Earth itself.

1302
00:44:49,115 --> 00:44:52,515
-- Sync, corrected by <font color=#00FF00>elderman</font> --
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