National Geographic: Mysteries Underground Page #3

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with almost a quarter mile

of rock overhead

can be oppressive, even terrifying.

But cavers like Bridges

relish the experience.

It's almost like coming back to home

after you've been gone for a while.

It's a very comfortable feeling to me,

particularly in that particular cave.

And you know it's a sense of isolation

The world becomes very simple

Here there is no day or night.

If they ignore the time,

cavers tend to stay awake,

and sleep,

for longer and longer periods.

In Lechuguilla Cave,

there is little evidence of life.

But this is rare.

Many caves harbor a hidden kingdom

of creatures, dominated by bats.

Bats thrive in darkness.

They navigate not by sight,

but by subtle patterns

of reflected sound.

Some caves are home to millions

of bats,

the greatest concentration

of mammals anywhere.

Their nitrogen-rich droppings,

or guano,

are harvested as a fertilizer.

Large deposits produce a toxic gas,

which can be lethal.

Mountains of bat guano support

the intricate food chain underground.

Sometimes, an injured bat, or a baby,

falls into the guano

and itself becomes food.

Within minutes the bat is reduced

to a skeleton.

Abundant underground, the cave cricket

Crickets spend much of their time

gathering food outside their caves,

but inside they perform

a vital role as scavengers.

In mute testament to their environment

fish have evolved here without eyes.

The salamander has dispensed

with eyes, too,

and has no need of skin pigment

in a world without sunlight.

People have probably always found

shelter in caves.

Thousands of years ago,

as much of the world still lay

in the grip of the last Ice Age,

prehistoric hunters left spectacular

evidence behind them.

The human spirit was born

and nurtured here,

its expression etched

on walls of stone.

By the early 20th century

most people lived elsewhere.

But science and curiosity drove some

to explore deeper underground.

Magnesium flares lit the way,

filling dark voids with light.

Geologists squeezed into

subterranean chambers

seeking to understand

their origin and structure.

And soon the ancient lure

of caves turned to profit.

Tourists went underground.

Then and now,

humans have been compelled

to seek out caves,

and to combat the gloom

with gay defiance.

In the United States,

New Mexico's Carlsbad Caverns

was declared a national park in 1930.

But natural wonders were not enough.

Carlsbad and other caves promoted

all sorts of attractions,

some a bit farfetched.

The time will come

when some master musician

in the Carlsbad Cavern will

be able to create s symphony in stone

Many parts of the world

are known for caves.

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