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BBC Natural

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Hidden in this jungle

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3000 years of human history

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one of the world's greatest ancient civilisations.

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Here, on Mexico's Yucatan peninsula,

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the Maya built cities, temples and palaces

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and yet we still don't know how they thrived.

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The forest has grown back

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and nature has taken over again,

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leaving many riddles unsolved.

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Like the riddle of the missing river.

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Almost every other ancient civilisation
was founded beside a great river,

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but there are none here,

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not even any streams.

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Where is the Nile?

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The Ganges or the Euphrates of the Maya ?

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What they did have

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were thousands of these pretty little pools
scattered through the jungle.

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Called Cenotes,

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they are the Yucatan's only source of fresh water.

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Could they, by themselves,
have supported an entire civilisation?

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The Maya believe that Cenotes

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were entrances to another world,

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an underworld.

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At face-value they seem to be little
more than beautiful jungle waterholes,

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so was the underworld just a myth?

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People today can do something the Maya
could only have dreamt about

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breathe under water.

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These modern explorers have made
some remarkable discoveries,

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not only about the Maya,

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but about the forest

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and its animals, too.

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What they have found in the underworld,

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has changed our understanding of the Yucatan,

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forever.

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Secrets of the Maya Underworld
-= MVGroup =-

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The Yucatan,

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a peninsula the size of England,

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separating the Gulf of Mexico from the Caribbean Sea.

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American-born Sam Meecham is a cave diver.

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He has been exploring the waters under
the Yucatan for more than a decade,

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but he has still only seen a
fraction of what is down there.

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His mission

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is to explore as many Cenotes as he can,

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working with scientists to try to make sense of it all.

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The puzzle of the Yucatan peninsula
is extremely complex.

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I arrived here in 1994 with the intention
of only being here for six months,

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and 10 years later, I find myself still here,

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so interested and curious in what I have discovered.

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But Sam wasn't the first foreign explorer to be
drawn to Mexico's jungles by a passion for adventure.

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Back in 1839,

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John Lloyd Stevens,
an American diplomat and travel writer,

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set off into the Yucatan,

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inspired by rumours of a lost civilisation.

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For a while,

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he found nothing,

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even though clues lay all around him.

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Finally,

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he stumbled upon the ruins of a great city,

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smothered by the jungle.

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The wild tales that Stevens told

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made his name as a famous Victorian explorer,

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a hero of his time,

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and to some,

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the original Indiana Jones.

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Stevens' fantastic revelations have inspired
a whole new generation of explorers.

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For me, one of great motivating
factors in what we do here

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is that I am able to explore,
in the 21st century,

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something I thought would never
have been possible in my lifetime.

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Just getting to the Cenotes is
an adventure in itself.

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Like the Maya ruins, they are scattered over
thousands of square kilometres of trackless forest.

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But Sam is not alone

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British-born Steve Bogart shares
Sam's passion for exploration.

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They have been Cenote hunting together for years.

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With local help,

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they mount expeditions deep
into the Yucatan's interior.

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It can take days to find a new Cenote.

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As we travel through the jungle
looking for Cenotes,

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of course there is always the usual
assembly of spiny trees and cactuses.

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We have crocodiles, we have snakes, scorpions,
tarantulas, you name it, it's all there.

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But really,

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if you know what to look for and know
where to go and when not go,

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you can avoid a lot of these problems.

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Finally, a new, unexplored Cenote.

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Never mind the jungle treks,

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the real danger for Sam and Steve begins at
the bottom of these enchanting little pools,

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considered sacred by the Maya.

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It's very easy to see how the ancient Maya

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would have perceived the Cenotes
as very sacred spaces

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they are absolutely beautiful jewels
out in the middle of this jungle.

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And to walk up to the edge of a
Cenote and to look down

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into the crystal clear water and see the fish
swimming below in the natural daylight,

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casting these incredible shafts
of light through the water,

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is very inspiring.

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As the sole sources of water in this jungle,

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these pools are also magnets for wildlife,

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and to Cenote specialists like grebes,

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their whole world.

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With thick forest on all sides,

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they seem as isolated as islands in an ocean.

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Peccaries, deer and other forest animals
use Cenotes as watering holes,

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but that doesn't mean they are easy to see

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the jungle does it's best to keep them hidden.

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But some animals, you can't help but notice.

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Howler monkeys.

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Even if you don't see them at first,

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you are sure to hear them.

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With calls that carry five kilometres,

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they are the loudest land animals in the world.

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Howlers are sloppy eaters.

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Coatis following below can
fill their stomachs solely

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out of what they have dropped.

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Spider monkeys.

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They are infinitely quieter than howlers,

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but much more agile.

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With their hooking hands and long arms,

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these monkeys can live their entire
lives in the dense forest canopy.

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For nine months of the year,

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there is no rainfall here,

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and much of the forest struggles to survive.

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But some trees seem immune to the drought.

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What is their secret?

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Such are the riddles of the Yucatan.

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The answers lie underground.

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But Sam and Steve won't get
to go there until tomorrow.

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In the dark,

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the jungle seems even denser

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and the sounds,

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even stranger.

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This is when Cenotes really come alive.

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Tapiers love water,

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for bathing, as much as drinking.

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But visiting a Cenote means coming into the open,

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which, for good reason,

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they only do after dark.

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Like watering holes anywhere,

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Cenotes are where predators,

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in this case Jaguars,

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come to hunt.

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But to the Maya,

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Cenotes were more than just jungle watering holes,

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they were central to their world.

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Cities and temples were often
built right next to them.

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These sacred wells were gateways
to the underworld

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a terrifying place of spirits

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and of fearsome gods who demanded respect.

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At the bottom of many Cenotes

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lie offerings made to the underworld.

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For archaeologists,

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Cenotes are time-capsules that provide
clues to how the ancient Maya lived

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and died.

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Sometimes, even the people, themselves,

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were sacrificed to the gods they feared so much.

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Every pot and skeleton

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has its own story to tell.

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The discoveries of underwater explorers

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are helping archaeologists rewrite

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the Yucatan's ancient history.

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Yucatan's explorers

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aren't just interested in
the clues to Maya history

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that they might find at the
bottom of these pools.

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They want to know

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what might lie beyond them.

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Is there, indeed,

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an underworld?

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Could this Cenote be a gateway
to a whole new world?

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If it is,

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where does that world lead?

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Every new Cenote

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presents a new opportunity.

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Cenotes really present us with the truest
form of exploration found today.

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When we come up to the side of a Cenote,

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we literally have no idea
what we are going to find

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at the bottom of it,

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until we actually get in and investigate.

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And, for me, that is one of greatest
thrills about what we do.

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Cenotes aren't just simple pools,

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they are caves

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flooded caves whose roofs have collapsed.

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But Sam and Steve have yet to discover

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to what extent Cenotes are
connected to each other

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by flooded tunnels.

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If there is a network of
flooded tunnels down there,

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how far does it go?

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What they are doing is carefully charting an,
as-yet, uncharted part of the planet.

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Somewhere no other human being has ever gone.

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It's one of the riskiest things an explorer can do.

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This type of diving isn't for everybody.

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And, definitely, you have to want to do it,
in order to be involved in it.

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The first cave dive that I ever did, actually,

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I was pretty nervous.

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Talk to an astronaut that sat on top of a
rocket full of fuel and blasted off to the moon,

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sure I bet they were a little bit nervous,

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but look at what we've gained
through space exploration.

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All those people were willing to take
a risk to achieve an incredible goal.

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Sometimes there is hardly enough
room to squeeze through.

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Getting stuck or damaging vital equipment now

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would be fatal.

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We are diving in an extremely hostile environment.

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It is underwater, it's dark,
it's easy to get disoriented

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and therefore it is easy to have panic attacks.

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There is two ways out of a panic situation,

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luck and death.

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And therefore, panic is not an option for us.

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You really have to take three
deep breaths, calm yourself

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and assure yourself that you are able
to get out of that situation.

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Exploration is rarely without risks.

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But one of the biggest rewards

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is seeing something that
has never been seen before.

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What they have discovered down here

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is just staggering.

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The Maya did have an underworld.

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And it is as strange

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and as beautiful a place as
any myth might describe.

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They have revealed a vast
system of flooded caves,

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underpinning much of the peninsula.

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It has changed our view of the Yucatan, forever.

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In a sense,

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this is like exploring outer space,

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the weightlessness,

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the utter strangeness,

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the thrill of the unknown.

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Cave divers call this inner space.

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Sam has got close to a long held ambition.

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One of my childhood dreams
was to become an astronaut.

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I am not an astronaut now,

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but I feel that I am as close as I
can come to outer space exploration

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in the work that we do here.

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We are completely dependent
on life-support equipment,

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we travel into a completely
alien and foreign environment

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that we don't know a whole lot about.

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And many of the cave systems that we dive in

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have seen fewer visitors than
the surface of the moon.

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It's amazing to think that a whole
civilisation once sat on top of all this,

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trying to imagine what was down here.

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The reality of this place

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can be as surreal as anything
the Maya may have dreamt of.

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Sometimes, what seems to be air, isn't.

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It's just a different kind of water.

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Some caves contain layers
of water that just don't mix.

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There is so much about this system
that we don't yet understand.

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Sam and Steve's aim is to find
out how it all connects.

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They are making maps.

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Light ahead reveals a new Cenote.

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They will record it's position,

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then swim back to where they started
the dive and try to return here,

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overland.

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The more they explore,
the more connections they find.

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But they have got a long way to go.

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There are still thousands of
Cenotes left to investigate.

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The return journey is,
in many ways, more difficult.

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Underground, they went where
the tunnels led them.

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Up here,

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they are looking for one tiny
pool among thousands,

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hidden somewhere in a dense jungle.

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For this,

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they will need satellite positioning
and aerial photographs.

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00:20:04,760 --> 00:20:07,160
State-of-the-art technology gets them close,

259
00:20:07,360 --> 00:20:08,960
but on the final stretch,

260
00:20:09,520 --> 00:20:11,920
they get a helping hand from birds.

261
00:20:14,720 --> 00:20:16,880
Turquoise-browed Motmots.

262
00:20:17,320 --> 00:20:19,520
These are true Cenote birds,

263
00:20:20,120 --> 00:20:22,800
they feed on the abundant insects near the water

264
00:20:23,080 --> 00:20:25,240
and often nest inside the caves.

265
00:20:34,720 --> 00:20:36,120
Their distinctive call

266
00:20:36,120 --> 00:20:39,120
almost always means there is a Cenote nearby.

267
00:20:43,880 --> 00:20:47,080
It was the ancient Maya who first
used them as guides to water.

268
00:20:47,440 --> 00:20:49,240
This works just as well today.

269
00:20:58,320 --> 00:21:00,320
Now they have located the new Cenote,

270
00:21:00,520 --> 00:21:02,760
Sam and Steve need to find out

271
00:21:02,960 --> 00:21:05,960
if it has further connections
with other parts of the system.

272
00:21:08,520 --> 00:21:10,480
In our corner of the Yucatan peninsula,

273
00:21:10,480 --> 00:21:14,000
the collaborative efforts of cave
diving explorers have mapped

274
00:21:14,000 --> 00:21:22,080
and explored over 550 kilometres of
underground, underwater passageway

275
00:21:22,080 --> 00:21:24,760
in over a hundred different cave systems.

276
00:21:24,960 --> 00:21:28,120
The promise of future exploration is high,

277
00:21:28,120 --> 00:21:31,840
there is so much left that
we still have yet to explore.

278
00:21:40,120 --> 00:21:44,320
This may seem like nothing more than
an elaborate game of join-the-dots,

279
00:21:45,080 --> 00:21:47,800
but each time Sam and Steve
go back underground,

280
00:21:48,360 --> 00:21:51,240
they never lose sight of the
potential dangers of their work.

281
00:21:52,640 --> 00:21:57,320
One of the truisms of cave diving is
that 'complacency breeds death'.

282
00:21:57,840 --> 00:22:01,960
And every single dive we approach
as if it's the first dive we had done.

283
00:22:02,280 --> 00:22:06,560
And we have a ritual that we go
through of matching our gear,

284
00:22:06,560 --> 00:22:08,120
checking for leaks,

285
00:22:08,120 --> 00:22:12,160
and making sure that everything is
in optimal 100% condition for diving.

286
00:22:13,960 --> 00:22:16,920
Sam couldn't have a better dive buddy than Steve,

287
00:22:17,240 --> 00:22:19,960
he is one of the region's
most experienced cave divers

288
00:22:19,960 --> 00:22:21,600
and a master technician.

289
00:22:22,480 --> 00:22:24,400
He knows his equipment inside out.

290
00:22:30,760 --> 00:22:32,600
OK, one of the first things you will notice

291
00:22:32,600 --> 00:22:35,800
is that we are actually taking
two tanks with us, rather than one.

292
00:22:35,800 --> 00:22:39,760
That's because we are diving in an alien,
potentially hostile environment,

293
00:22:39,760 --> 00:22:42,040
and we need redundancy in
all our life-support equipment

294
00:22:42,040 --> 00:22:45,240
and gas supply is obviously
very very critical to us.

295
00:22:45,440 --> 00:22:49,160
We also use a gas management planning
rule know as a rule of thirds,

296
00:22:49,160 --> 00:22:52,000
so we would use one third of ou
 gas swimming into the cave,

297
00:22:52,000 --> 00:22:53,800
one third swimming back out again,

298
00:22:53,800 --> 00:22:56,120
so that when we surface
we have one third in reserve.

299
00:22:56,120 --> 00:22:57,680
And that is an emergency reserve,

300
00:22:57,960 --> 00:23:00,560
should it take it us longer to
exit than we anticipated

301
00:23:00,560 --> 00:23:02,720
or if we needed to share air with a buddy.

302
00:23:11,040 --> 00:23:13,120
A thin piece of white string,

303
00:23:13,120 --> 00:23:14,400
carefully laid,

304
00:23:14,600 --> 00:23:16,800
quite literally becomes their lifeline.

305
00:23:18,040 --> 00:23:21,040
It may be the only way that
they can find their way back

306
00:23:21,440 --> 00:23:22,960
out of the labyrinth.

307
00:23:37,280 --> 00:23:41,400
They mark it with arrows that always
point back towards the entrance

308
00:23:41,480 --> 00:23:42,720
and safety.

309
00:23:45,520 --> 00:23:47,200
It is also a measuring tape

310
00:23:47,800 --> 00:23:51,520
regularly spaced knots tell Sam
and Steve how far they have gone.

311
00:23:57,280 --> 00:23:58,760
As we explore the cave systems,

312
00:23:58,760 --> 00:24:01,320
we try to be smart as we can

313
00:24:01,320 --> 00:24:05,160
and generally, we are trying to
go in a particular direction.

314
00:24:05,200 --> 00:24:08,880
And we have compasses that work
under water and using those compasses,

315
00:24:08,880 --> 00:24:11,880
we are able to determine which route to take.

316
00:24:16,960 --> 00:24:21,280
It is quite common to come
up to a split in a passageway.

317
00:24:21,800 --> 00:24:24,800
We have to determine which is
the best route to take.

318
00:24:24,800 --> 00:24:26,840
In some cases, that will end up in a dead-end

319
00:24:26,840 --> 00:24:29,520
and we turn around and come back
out and try the other way.

320
00:24:39,280 --> 00:24:41,000
Using spools of string,

321
00:24:41,080 --> 00:24:45,320
Yucatan's cave divers have measured the
longest underwater cave in the world

322
00:24:45,520 --> 00:24:48,440
over 133 kilometres long.

323
00:24:52,040 --> 00:24:56,720
Exploration wouldn't be exploration if
everything always went to plan.

324
00:24:57,480 --> 00:24:58,560
This time,

325
00:24:58,560 --> 00:25:01,480
the divers have come to a passage
too tight to squeeze through

326
00:25:02,280 --> 00:25:03,600
and they are forced to stop.

327
00:25:06,760 --> 00:25:08,560
They follow their safety line back,

328
00:25:08,960 --> 00:25:10,640
and live to dive another day.

329
00:25:12,120 --> 00:25:15,920
But explorers wouldn't be explorers if they
let such setbacks discourage them.

330
00:25:16,240 --> 00:25:18,200
There is always the thrill of the next dive.

331
00:25:21,280 --> 00:25:24,640
It's pretty-much guaranteed
that every time we go into a Cenote

332
00:25:24,640 --> 00:25:26,960
it is going to be a different experience,
it's something new,

333
00:25:26,960 --> 00:25:30,600
it's something exciting, and that's
what really draws me in.

334
00:25:32,000 --> 00:25:34,040
One of many interesting things of diving here

335
00:25:34,040 --> 00:25:37,880
is to watch all the wildlife that thrives
in the crystal clear water.

336
00:25:39,280 --> 00:25:41,520
That includes sailfin mollies,

337
00:25:41,520 --> 00:25:42,600
small fish

338
00:25:42,760 --> 00:25:46,920
that stick to the bright sunlit zones
in the open water pools of Cenotes.

339
00:25:48,040 --> 00:25:50,360
For a male, it is a hectic life.

340
00:25:50,880 --> 00:25:53,440
He has a three-dimensional territory to patrol

341
00:25:53,640 --> 00:25:56,280
and is constantly chasing other males out

342
00:25:56,600 --> 00:25:59,000
while trying to keep his harem of females in.

343
00:26:04,360 --> 00:26:08,720
In both cases, success depends on how
effectively he displays his sail fin.

344
00:26:11,360 --> 00:26:13,680
It's a big job for a little fish.

345
00:26:31,120 --> 00:26:33,200
Some fish, like these tetras,

346
00:26:33,400 --> 00:26:35,520
have proved to be real opportunists.

347
00:26:36,400 --> 00:26:40,800
They have learnt to follow divers' torches
into the dark to feed right inside the caves.

348
00:26:45,760 --> 00:26:49,600
Our divers take care not to bring
any uninvited guests with them,

349
00:26:50,320 --> 00:26:53,800
because the underworld has
its own unique creatures

350
00:26:54,160 --> 00:26:56,960
an entire food chain of over 30 species

351
00:26:57,160 --> 00:27:00,200
that live out their lives in the pitch dark.

352
00:27:09,080 --> 00:27:10,920
Most cave animals are white,

353
00:27:11,480 --> 00:27:13,160
because in a world without light,

354
00:27:13,160 --> 00:27:14,840
colour is pointless.

355
00:27:15,720 --> 00:27:17,360
Even eyes are useless,

356
00:27:17,760 --> 00:27:19,680
and many creatures just don't have them.

357
00:27:22,560 --> 00:27:23,520
Down here,

358
00:27:23,640 --> 00:27:27,160
touch and smell are all that matter.

359
00:27:30,000 --> 00:27:33,400
Among the strangest and most
ancient of cave beasts

360
00:27:33,480 --> 00:27:34,720
is the remipede

361
00:27:35,240 --> 00:27:37,800
a sort of primitive centipede that is rarely seen

362
00:27:37,800 --> 00:27:40,440
found only in waters exceptionally low in oxygen.

363
00:27:41,160 --> 00:27:43,920
Relics of one of the earliest
chapters of life on Earth,

364
00:27:44,160 --> 00:27:46,320
they are among the caves' top predators,

365
00:27:46,800 --> 00:27:49,400
coming the water for shrimps and isopods.

366
00:27:52,920 --> 00:27:55,600
If the remipede doesn't seem
to know which way is up,

367
00:27:55,920 --> 00:27:57,040
that's because,

368
00:27:57,120 --> 00:27:59,000
in the water and in the dark,

369
00:27:59,520 --> 00:28:01,800
up and down aren't so relevant.

370
00:28:15,840 --> 00:28:17,320
In the underworld,

371
00:28:17,320 --> 00:28:19,160
even the fish are surreal

372
00:28:19,360 --> 00:28:20,600
ghostly white,

373
00:28:20,720 --> 00:28:22,760
with blanks where eyes should be.

374
00:28:27,520 --> 00:28:29,680
There are other signs of life down here.

375
00:28:33,520 --> 00:28:36,200
This is the perfectly preserved tooth

376
00:28:36,480 --> 00:28:37,840
of a Gomphotherium,

377
00:28:38,320 --> 00:28:42,240
a relative of the elephant that
has been extinct for 10,000 years.

378
00:28:48,240 --> 00:28:49,920
Ancient animal remains,

379
00:28:49,920 --> 00:28:52,480
and these stalactites and stalagmites

380
00:28:52,680 --> 00:28:54,760
only ever formed in air,

381
00:28:55,160 --> 00:28:59,120
are hard evidence that these caves used to be dry.

382
00:29:00,200 --> 00:29:02,840
And Yucatan's history goes deeper still

383
00:29:03,360 --> 00:29:06,200
the walls of these caves
are made of soft limestone,

384
00:29:06,400 --> 00:29:10,560
telling us that this was once a huge coral reef.

385
00:29:26,040 --> 00:29:28,360
Some caves near the surface have air pockets

386
00:29:28,360 --> 00:29:31,640
and cracks in their ceilings that
allow bats to come and go.

387
00:29:32,280 --> 00:29:33,680
Cave swifts, too.

388
00:29:34,240 --> 00:29:37,320
It's the perfect sheltered place
to roost and nest.

389
00:29:38,960 --> 00:29:41,880
No wonder the Maya thought that
bats were from the underworld.

390
00:29:42,440 --> 00:29:45,840
They would have seen them flying straight
out of the ground, as night fell.

391
00:29:49,960 --> 00:29:51,720
By exploring underground,

392
00:29:51,960 --> 00:29:55,760
Yucatan's divers are peeling back
the many layers of the peninsula,

393
00:29:55,960 --> 00:30:00,320
and are slowly revealing the incredible
relationship between its flooded caves

394
00:30:00,400 --> 00:30:02,800
and everything they affect at the surface.

395
00:30:06,680 --> 00:30:09,640
There are many ways in which
these two worlds connect.

396
00:30:12,200 --> 00:30:13,280
Tree roots.

397
00:30:15,320 --> 00:30:17,800
This is the jungle's secret.

398
00:30:18,000 --> 00:30:20,280
How, with hardly any surface water,

399
00:30:20,280 --> 00:30:22,760
it can still grow so dense.

400
00:30:24,600 --> 00:30:28,520
Some trees and vines push their
roots through gaps in the limestone

401
00:30:28,520 --> 00:30:30,800
to the permanent water supply below.

402
00:30:33,120 --> 00:30:35,560
It doesn't matter how dry it gets on the surface,

403
00:30:35,680 --> 00:30:38,080
they rely on the underworld.

404
00:30:39,440 --> 00:30:44,200
These deep-rooted trees provide animals
with a year-round supply of leaves,

405
00:30:44,200 --> 00:30:46,400
flowers and fruit.

406
00:30:55,040 --> 00:30:58,760
This vital connection between the
forest and the ground beneath it,

407
00:30:58,960 --> 00:31:00,720
must have intrigued the Maya.

408
00:31:01,200 --> 00:31:05,040
It could only have reinforced their
belief in the power of the underworld.

409
00:31:07,120 --> 00:31:09,560
They, too, relied on its gift of water.

410
00:31:10,920 --> 00:31:12,200
A few Cenotes

411
00:31:12,400 --> 00:31:16,640
could help a whole city survive
even the harshest of dry seasons.

412
00:31:26,000 --> 00:31:29,840
But Sam doesn't just look to archaeology
for his understanding of the Maya

413
00:31:30,360 --> 00:31:31,640
he can talk to them.

414
00:31:33,480 --> 00:31:36,600
Direct descendants of the
ancient Maya still live here.

415
00:31:39,640 --> 00:31:40,480
One of them,

416
00:31:40,560 --> 00:31:42,680
is Don Fermin Zippe,

417
00:31:42,800 --> 00:31:44,360
a good friend of Sam's.

418
00:31:51,880 --> 00:31:54,440
The Maya still practice slash and burn farming

419
00:31:54,760 --> 00:31:58,280
growing crops then letting the forest
grow back to replenish the soil.

420
00:31:59,440 --> 00:32:02,920
In fact, the ancient Maya
did this on a grand scale.

421
00:32:03,360 --> 00:32:04,360
Incredibly,

422
00:32:04,360 --> 00:32:07,640
most of the jungle here,
previously thought to be pristine,

423
00:32:07,640 --> 00:32:12,120
has actually been cut down and regrown
many times over the last 2000 years.

424
00:32:16,440 --> 00:32:19,120
The Maya may have stopped building
large cities and temples,

425
00:32:19,400 --> 00:32:21,760
but they live-on today as skilful farmers,

426
00:32:21,960 --> 00:32:25,640
thriving, despite the thin soils
and harsh seasons of the Yucatan.

427
00:32:42,120 --> 00:32:44,520
Maya communities are close-knit

428
00:32:44,720 --> 00:32:47,440
and the Mayan language is still spoken.

429
00:33:04,120 --> 00:33:07,600
"Cenote" is derived from the
Maya world word for "well".

430
00:33:08,120 --> 00:33:10,240
Almost every village is built around one.

431
00:33:10,880 --> 00:33:14,280
Other Cenotes mark boundaries
between the communities.

432
00:33:22,400 --> 00:33:25,560
Cenotes were, and are, quite literally

433
00:33:25,560 --> 00:33:27,080
central to their world.

434
00:33:35,520 --> 00:33:37,440
As well as a distinct language,

435
00:33:37,440 --> 00:33:39,760
the Maya have a distinct set of beliefs.

436
00:33:40,400 --> 00:33:43,640
Their stories and fables,
passed down the generations,

437
00:33:44,000 --> 00:33:45,880
describe everything around them

438
00:33:46,520 --> 00:33:51,880
the Cenotes, the jungle, the animals.

439
00:33:55,760 --> 00:33:59,360
One Maya belief is that the
powerful forces of the underworld

440
00:33:59,480 --> 00:34:01,280
determine their prosperity

441
00:34:01,640 --> 00:34:03,040
and their destiny.

442
00:34:09,640 --> 00:34:12,640
Don Fermin still practices the Maya religion.

443
00:34:13,320 --> 00:34:15,640
He prays to the gods of his ancestors

444
00:34:16,040 --> 00:34:17,640
and regards Cenotes

445
00:34:17,920 --> 00:34:19,760
as windows into their world.

446
00:34:25,160 --> 00:34:27,920
In advance of Sam's more difficult dives,

447
00:34:28,120 --> 00:34:31,520
Don Fermin sometimes makes
offerings to the underworld,

448
00:34:32,040 --> 00:34:33,720
asking for a safe passage.

449
00:34:35,000 --> 00:34:37,640
And this dive will be difficult.

450
00:34:41,880 --> 00:34:46,040
But it will reveal yet another twist in
the Yucatan's many-layered history

451
00:34:46,800 --> 00:34:48,200
a cosmic event

452
00:34:48,200 --> 00:34:50,800
that affected not only the
world of the ancient Maya,

453
00:34:51,280 --> 00:34:52,400
but possibly,

454
00:34:52,640 --> 00:34:54,360
the rest of the world as well.

455
00:34:59,280 --> 00:35:02,600
Some Cenotes near the north
western tip of the Yucatan

456
00:35:02,840 --> 00:35:06,080
aren't at all like the ones that Sam
and Steve are used to exploring.

457
00:35:07,680 --> 00:35:09,000
These are much deeper,

458
00:35:09,120 --> 00:35:11,680
sheer, vertical sink holes,

459
00:35:12,200 --> 00:35:13,960
known as "Pit Cenotes".

460
00:35:22,280 --> 00:35:24,520
This Cenote is definitely a lot deeper than

461
00:35:24,520 --> 00:35:26,640
ones that we normally would encounter.

462
00:35:26,760 --> 00:35:31,040
Today we got to about 45 metres of depth
and still we couldn't see the bottom.

463
00:35:38,600 --> 00:35:40,520
This appears to be the bottom,

464
00:35:41,200 --> 00:35:42,280
but it isn't.

465
00:35:43,360 --> 00:35:45,360
It is a cloud of hydrogen sulphide,

466
00:35:45,640 --> 00:35:47,440
made from rotting vegetation.

467
00:35:50,480 --> 00:35:52,560
It is toxic and corrosive

468
00:35:53,080 --> 00:35:55,000
not somewhere you would want to hang around.

469
00:36:04,280 --> 00:36:07,200
The hydrogen sulphide layer
is actually pretty intense,

470
00:36:07,200 --> 00:36:09,400
as you are descending down into the Cenote,

471
00:36:09,400 --> 00:36:12,160
it gives the appearance that
you are coming up on the floor

472
00:36:12,200 --> 00:36:15,840
and all of a sudden you realise
it is not the floor, it is a cloud.

473
00:36:15,840 --> 00:36:19,800
It is made up of sulphur, primarily,
so it has got a rotten egg smell to it.

474
00:36:19,800 --> 00:36:22,440
In extreme cases, where it is very strong,

475
00:36:22,440 --> 00:36:25,240
you can feel it burning any
exposed skin that you have.

476
00:36:46,720 --> 00:36:48,960
Why are these Cenotes so different?

477
00:36:50,000 --> 00:36:53,800
They are evidence of a critical turning
point in the Yucatan's distant history

478
00:36:54,400 --> 00:36:57,120
something that was only noticed 20 years ago,

479
00:36:57,640 --> 00:37:01,080
when satellites gave us a new
perspective on life on Earth.

480
00:37:06,240 --> 00:37:08,880
If you look at normal Cenotes from space,

481
00:37:09,160 --> 00:37:12,120
their pattern is scattered and random,

482
00:37:14,160 --> 00:37:15,720
but the Pit Cenotes,

483
00:37:15,920 --> 00:37:17,760
form a distinct semicircle,

484
00:37:17,960 --> 00:37:20,360
165 kilometres across.

485
00:37:23,880 --> 00:37:26,920
Seismic studies have shown
that the circle is completed

486
00:37:26,920 --> 00:37:28,120
under the sea.

487
00:37:28,920 --> 00:37:31,880
So what does this huge circle represent?

488
00:37:32,720 --> 00:37:36,280
The answer lies at least 65 million years ago,

489
00:37:36,720 --> 00:37:39,920
when the Yucatan was a shallow tropical sea.

490
00:37:41,120 --> 00:37:43,560
The disastrous event that caused the circle

491
00:37:43,960 --> 00:37:46,240
was so massive, that some think

492
00:37:46,480 --> 00:37:49,040
it could have led to the demise of the dinosaurs.

493
00:37:51,520 --> 00:37:53,240
An enormous meteor,

494
00:37:55,360 --> 00:37:57,240
heading for what is now the very tip

495
00:37:57,240 --> 00:37:59,080
of the Yucatan peninsula.

496
00:38:15,440 --> 00:38:20,520
Imagine at the moment that this
meteor slammed into our planet,

497
00:38:20,520 --> 00:38:24,760
it was so huge that if one edge
of it was touching our planet,

498
00:38:24,760 --> 00:38:30,120
the outer edge of it would be at the same
altitude as a commercial jet liner flies today.

499
00:38:30,320 --> 00:38:32,040
The immense impact crater

500
00:38:32,040 --> 00:38:34,280
was gradually buried under limestone,

501
00:38:34,480 --> 00:38:37,520
built up by coral reefs over millions of years.

502
00:38:38,320 --> 00:38:39,760
But the crater's shape

503
00:38:39,760 --> 00:38:41,760
was echoed in the way this limestone,

504
00:38:41,760 --> 00:38:45,600
then eroded to form the distinctive
semicircle of Pit Cenotes.

505
00:38:48,400 --> 00:38:49,880
When the Maya arrived,

506
00:38:50,000 --> 00:38:53,320
they built great cities and temples
around these sacred wells,

507
00:38:53,720 --> 00:38:57,760
unwittingly outlining the footprint
of this global catastrophe.

508
00:39:01,240 --> 00:39:02,160
Once again,

509
00:39:02,160 --> 00:39:06,080
the Yucatan's history can be read
by looking deep into its landscape.

510
00:39:10,520 --> 00:39:13,000
But it has one more secret to reveal,

511
00:39:13,360 --> 00:39:15,720
one last riddle to be solved.

512
00:39:28,720 --> 00:39:30,240
When it does rain here,

513
00:39:30,640 --> 00:39:32,040
it rains hard.

514
00:39:36,440 --> 00:39:38,360
But this huge amount of water

515
00:39:38,880 --> 00:39:40,560
doesn't settle on the ground,

516
00:39:41,440 --> 00:39:42,560
it vanishes.

517
00:39:44,400 --> 00:39:46,320
It seeps through the limestone

518
00:39:47,120 --> 00:39:48,440
into the underworld.

519
00:39:51,000 --> 00:39:54,520
But this freshwater is only the top layer

520
00:39:55,080 --> 00:39:59,400
it floats above an enormous body
of much heavier, salt water.

521
00:40:00,840 --> 00:40:02,440
This is the halocline

522
00:40:02,800 --> 00:40:04,560
the interface between the two.

523
00:40:06,120 --> 00:40:09,080
It is this contrast between
the gin-clear fresh water

524
00:40:09,320 --> 00:40:12,520
and the hazier, salt water
that can make diving here

525
00:40:12,720 --> 00:40:13,800
so surreal.

526
00:40:21,000 --> 00:40:22,320
Divers have discovered

527
00:40:22,520 --> 00:40:24,320
that the freshwater here

528
00:40:24,800 --> 00:40:26,800
does more than just float.

529
00:40:30,960 --> 00:40:32,240
It flows,

530
00:40:32,560 --> 00:40:34,680
in huge underground rivers,

531
00:40:35,200 --> 00:40:39,320
probably the largest underground
river system in the world.

532
00:40:45,920 --> 00:40:48,080
Nearly two centuries ago,

533
00:40:48,720 --> 00:40:52,440
John Lloyd Stevens rediscovered
the Maya civilisation.

534
00:40:53,600 --> 00:40:57,400
People have long wondered how
they thrived without a great river.

535
00:40:59,280 --> 00:41:00,040
Now,

536
00:41:00,840 --> 00:41:02,920
we appear to have found their Nile.

537
00:41:08,160 --> 00:41:10,640
These great rivers must flow out to sea,

538
00:41:10,960 --> 00:41:11,920
but where?

539
00:41:12,200 --> 00:41:14,080
Sam needs to find out.

540
00:41:16,080 --> 00:41:18,520
He comes across the skeleton of a manatee,

541
00:41:18,960 --> 00:41:20,160
a sea mammal.

542
00:41:20,840 --> 00:41:22,240
He must be getting close.

543
00:41:32,840 --> 00:41:34,080
Meter by meter,

544
00:41:34,360 --> 00:41:36,200
Cenote to Cenote,

545
00:41:37,120 --> 00:41:40,240
cave divers are mapping the
rivers from source to sea.

546
00:41:43,760 --> 00:41:44,960
But while doing so,

547
00:41:45,720 --> 00:41:47,800
they have made an alarming discovery.

548
00:41:54,280 --> 00:41:56,280
The modern world is taking over.

549
00:42:01,000 --> 00:42:06,000
I am amazed at the change that has taken
place in such a short time in this area.

550
00:42:06,000 --> 00:42:08,320
It seems that every time I go out of my door,

551
00:42:08,320 --> 00:42:10,640
there is a new building that has been built.

552
00:42:11,240 --> 00:42:14,240
The coastal strip of Cancun and the Riviera Maya

553
00:42:14,240 --> 00:42:17,320
is one of the fastest-growing
tourist areas in the world.

554
00:42:17,600 --> 00:42:19,400
There is one specific occasion where we were

555
00:42:19,400 --> 00:42:22,800
actually diving beneath a major
construction project.

556
00:42:23,000 --> 00:42:27,320
And, as we were diving along,
the entire cave was literally shaking

557
00:42:27,320 --> 00:42:28,880
as we were diving through it.

558
00:42:29,240 --> 00:42:32,120
And it wasn't until the
next day that we came back

559
00:42:32,440 --> 00:42:36,960
that we realised that they had been
perforating through the ceiling of the cave,

560
00:42:36,960 --> 00:42:40,360
and along one of the lines that
Steve had laid the previous day,

561
00:42:40,360 --> 00:42:45,120
there was actually a cement piling going
right down through the cave system.

562
00:42:45,480 --> 00:42:48,640
New construction could inadvertently block

563
00:42:48,880 --> 00:42:52,000
or pollute the great underground
rivers of the Yucatan

564
00:42:52,120 --> 00:42:55,840
with far-reaching effects,
still too complex for us to understand.

565
00:42:56,520 --> 00:42:57,880
The Maya underworld

566
00:42:57,880 --> 00:43:01,160
faces a new chapter in it's
long and varied history.

567
00:43:06,080 --> 00:43:08,360
The decline of the ancient Maya

568
00:43:08,760 --> 00:43:10,280
could teach us a thing or two.

569
00:43:13,280 --> 00:43:16,280
Some say they developed too far, too fast.

570
00:43:17,080 --> 00:43:17,960
Others,

571
00:43:18,600 --> 00:43:21,360
that a succession of droughts
left them without water.

572
00:43:26,240 --> 00:43:29,920
Everyone here still relies on the underworld.

573
00:43:30,480 --> 00:43:33,840
It is, and always was,
the lifeblood of the peninsula.

574
00:43:34,320 --> 00:43:35,040
Without it,

575
00:43:35,560 --> 00:43:37,360
the Yucatan would be a hot,

576
00:43:37,880 --> 00:43:40,640
dry and hostile place.

577
00:43:47,080 --> 00:43:49,360
By mapping the course of every river to the sea,

578
00:43:49,680 --> 00:43:53,160
Sam and other divers are hoping
to draw attention to them,

579
00:43:53,160 --> 00:43:55,480
so further damage can be avoided.

580
00:44:03,000 --> 00:44:06,640
Their work has not only helped us
to understand the Yucatan's past,

581
00:44:07,000 --> 00:44:09,080
but it can help to safeguard its future.

582
00:44:15,400 --> 00:44:17,440
Sam's journey down this river

583
00:44:17,880 --> 00:44:19,000
is nearly over.

584
00:44:19,840 --> 00:44:22,080
There is more light and more air,

585
00:44:22,720 --> 00:44:25,520
and the roots are roots of mangroves.

586
00:44:28,280 --> 00:44:29,520
And there are manatees.

587
00:44:33,280 --> 00:44:38,000
These gentle herbivores come to the
underworld's outflow to drink fresh water

588
00:44:38,400 --> 00:44:39,400
and to cool off.

589
00:44:40,040 --> 00:44:41,360
What they mean to Sam,

590
00:44:42,040 --> 00:44:43,400
is that he has made it.

591
00:44:56,360 --> 00:44:58,520
One last tunnel,

592
00:45:01,880 --> 00:45:04,440
and a journey that began in a jungle pool,

593
00:45:04,720 --> 00:45:06,920
ends-up off a Caribbean beach.

594
00:45:09,520 --> 00:45:11,440
Tomorrow he will be back in the forest,

595
00:45:11,520 --> 00:45:13,120
looking for a new Cenote

596
00:45:13,480 --> 00:45:14,760
and the next river.

597
00:45:15,280 --> 00:45:18,320
And when all the Cenotes are explored
and all the maps are finished,

598
00:45:18,600 --> 00:45:21,040
maybe the Yucatan will be better understood.

599
00:45:29,760 --> 00:45:31,360
In a more mystical way,

600
00:45:31,640 --> 00:45:33,480
the ancient Maya understood it.

601
00:45:34,400 --> 00:45:36,960
They knew they were at the
mercy of the underworld.

602
00:45:41,240 --> 00:45:42,520
At the ruins,

603
00:45:42,520 --> 00:45:46,520
archaeologists are revealing
ever-more about this great civilisation

604
00:45:46,800 --> 00:45:48,000
how they lived,

605
00:45:48,000 --> 00:45:49,320
and what they believed.

606
00:45:53,440 --> 00:45:54,480
But now,

607
00:45:54,480 --> 00:45:58,200
a whole new frontier has opened, underground.

608
00:46:05,320 --> 00:46:10,840
Sam and Steve are not the first explorers to have
been enchanted by the riddles of the Yucatan,

609
00:46:11,120 --> 00:46:16,000
but they have, quite literally,
taken exploration to a whole new level.

610
00:46:19,600 --> 00:46:22,200
To this day, it is only thought
that we have charted

611
00:46:22,200 --> 00:46:24,320
a fraction of the Maya underworld

612
00:46:24,320 --> 00:46:28,560
and many of these areas still
remain untouched and uncharted.

613
00:46:33,880 --> 00:46:36,120
Sam continues with his passion.

614
00:46:36,760 --> 00:46:39,480
He certainly has his work cut-out
for him in the coming years.

615
00:46:43,160 --> 00:46:47,080
My feelings about exploration can
be very easily summarised in a poem

616
00:46:47,080 --> 00:46:49,320
I read about the Yukon goldrush.

617
00:46:49,320 --> 00:46:52,320
And in that, the author says, "it is not the gold,

618
00:46:52,320 --> 00:46:54,120
it's finding the gold".

619
00:46:55,080 --> 00:46:58,760
It's finding the Cenote and diving down
into it and seeing what is there

620
00:46:58,760 --> 00:47:00,800
that really is the thrill for me.

621
00:47:04,320 --> 00:47:05,400
Really for all of us,

622
00:47:05,400 --> 00:47:08,480
it is a motivation to think that
you can live in the 21st-century

623
00:47:08,520 --> 00:47:10,480
and still be able to explore.

624
00:47:11,880 --> 00:47:15,360
We are only just scratching
the surface of what exists here.

625
00:47:15,600 --> 00:47:19,680
I have absolutely no doubt that
this place will continue to provide

626
00:47:19,680 --> 00:47:23,160
incredible scientific discoveries
for years to come.

627
00:47:26,640 --> 00:47:28,880
Sam and his explorer colleagues

628
00:47:28,880 --> 00:47:30,240
have risky,

629
00:47:30,240 --> 00:47:32,680
yet fascinating days ahead of them

630
00:47:33,120 --> 00:47:35,240
unveiling the many secrets

631
00:47:35,640 --> 00:47:37,560
of the Maya underworld.

632
00:47:45,560 --> 00:48:00,520
-= MVGroup =-