Lost Worlds: Life in the Balance

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It was once the heart of the

Mayan civilization

that stretched across

Central America -

a great city known as Tikal.

Its temples were the tallest

in the Western world...

monuments to its kings

and architects.

For centuries, Tikal grew larger...

its arts and sciences flourished.

Then, a thousand years ago,

at the height of its power,

the city was suddenly abandoned.

What happened in this lost world?

What keeps all cities, all

civilizations, alive... then and now?

Cities like New York are

triumphs of human technology -

they feel as if they will

last forever.

And they give us the sense that

we're somehow apart

from the rest of nature.

In big cities, it's easy to

take a lot of things for granted:

Food comes from the supermarket...

water comes from the faucet...

or does it?

Eight million New Yorkers drink clean

water from the Catskill mountains,

a hundred miles away.

If New York had to build water -

purification plants,

it would cost billions.

Here, nature provides that service,

free of charge.

If we could follow the rainfall

down through the leaf litter,

we'd find that

what we think of as "dirt"

is a world teeming with life -

a metropolis much more densely

populated than the city it serves.

In every square inch,

billions of microbes and other

organisms go about their business,

building and enriching the soil

we grow our food in...

helping condition the air

we breathe...

and cleaning the rainwater on its way

downhill to the reservoirs.

It's just one example of what

scientists call biological diversity -

the variety of interconnecting life

that keeps things healthy...

all over the planet

Everywhere, natural has found ways

to thrive.

Each place... each ecosystem...

shapes its own community

of plants and animals.

In every ecosystem, there is a balance

of relationships that keeps it working.

The giant seaweed called kelp...

is many things to many creatures.

It's a hiding place...

It's a nursery

for spawning fish...

and it's a food supply

for the sea urchin,

a spiny creature

with a big appetite.

If there are too many of them,

urchins can virtually clear-cut

the underwater forest

Until the 1970s, this was happening

along the California coast,

all because an animal that

belongs here was missing...

an animal that loves to eat urchins -

the sea otter.

It had been hunted almost to

extinction for its thick coat of fur.

Then, people decided to protect

the sea otter by law,

and their numbers grew...

the balance of life began to

re-establish itself.

Now, wherever there are otters,

the kelp forest flourishes and

so does everything in it

In the tropical forest, biological

diversity reaches its peak.

There are countless opportunities and

life seems to seize them all.

Like the kelp forest,

the health of the rain forest

is maintained by the variety

of its inhabitants -

as long as the natural balance

is undisturbed.

Animals can't live without the

habitats they're adapted to.

Many, like the South American tapir,

are now threatened or endangered

because they're losing the places

they live.

The forests are shrinking.

For thousands of years, more than

a third of Earth's land mass was

covered with pristine forests,

full of life.

The forests of China and lands

around the Mediterranean

were first to be cut...

as towns became cities and nations.

The rate of loss speeded up

with the Industrial Revolution.

But in the last 50 years,

we've cleared more forest

than in our previous history.

Less than half is left

Scientists estimate that thousands of

species of animals, plants, insects,

and other organisms are being

driven to extinction each year,

with unknown consequences.

We are changing the world

too quickly for animals

to be able to change with it

In major institutions around the world,

scientists are now working against time,

to find and understand all the

diversity of life that remains.

Nearly two million species from beetles

to blue whales, have been classified,

but there could be ten times that many,

still undiscovered.

The priority now is to

explore the places

with the most unique biodivercity...

where the web of life

is still intact

Fabian Michelangeli of the American

Museum of Natural History

is going back to his native Venezuela

to join a Rapid Assessment on an expedition...

to the fabled "Lost World" that inspired

the novel by Sir Arthur Conan Doyle.

I don't think we'll find a dinosaur

on this trip,

but in all of South America,

there's no place more incredible

than the table mountains

of Southern Venezuela.

The expedition is being organized in

the capital of Venezuela - Caracas.

Leader of the Rapid Assessment is biologist Margarita Lampo,

whose specialty is amphibians.

I always had a passion for animals,

ever since I was a little kid,

I liked the idea that everything

in nature

was connected to something else.

For ten years now,

I've been studying frogs and toads.

These creatures can tell us so much

about the health of the places

where they live.

My colleague Celsi Senaris and I

are concerned by evidence that

frog populations are declining

all over the world.

Now we have the chance

to search for them

in a place few people

have ever been.

For the next few weeks, we'll be

living in very different conditions.

We're heading southeast towards Canaima.

The plan is to meet our guide

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