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Deep in the heart of the Guadalupe Mountains in southern New Mexico,
rock-eating microbes are at work. But their appetite is dainty
compared to their voracious hunger millions of years ago, when they
carved some of the most impressive caves in the world. "Mysterious
Life of Caves" reports on a revolutionary theory of cave formation
that has startling implications for the development of life on Earth
and on other planets.
NOVA's team descends through miles of twisting, plunging caverns,
including some of the most exotic in the world that are off limits
to all except researchers. NOVA was given special permission to film
in these fragile, often perilous places, which have turned the
science of speleology on its head.
For all its evident risks, speleology is a science in which women
are especially prominent, including several featured in this
program: microbiologist and Mars specialist Penny Boston, geologist
Carol Hill, biologist
Diana Northup, and
geologist Louise Hose, among others.
"The first couple of times I went on trips [to Lechuguilla Cave], I
kept thinking, all I have to do is live long enough to get out and
then I never have to come back," admits Boston. "[But then] the
beauties of the cave ... really soaked into my soul." And so did the
science. The film crew's first stop is Lechuguilla, along with
Carlsbad Caverns, both in Carlsbad Caverns National Park, New
Mexico. Both are home to the most spectacular and puzzling gypsum
formations ever found.
Traditional theories of cave formation could not explain how these
vast subterranean caverns with massive gypsum deposits were formed.
Most limestone caves are dissolved by flowing water that has
absorbed carbon dioxide from the atmosphere and become slightly
acidic. However, gypsum is soluble in water and should have been
washed away at Carlsbad and Lechuguilla. Furthermore, there is no
sign that flowing water ever entered or exited the caves.
Whatever process created Carlsbad and Lechuguilla is largely dormant
now. So the team visits a more active and dangerous cavern: Cueva de
Villa Luz in Mexico, which emits the toxic, rotten-egg smell of
hydrogen sulfide from its entrance. Inside, explorers must wear
respirators and carry poison-gas monitors to protect themselves from
the hydrogen sulfide that reacts with water in the cave to form
caustic sulfuric acid. Deep within, they discover "snottites,"
mucous-like stalactites of sulfur-eating bacteria that also drip
sulfuric acid. Oddly enough, the noxious environment teems with
microbes, spiders, insects, crabs, and fish—all thriving in
complete darkness.
As strange as it may seem, sulfuric acid produced by microbial life
is the cause of about five percent of all limestone caves, including
Cueva de Villa Luz, Carlsbad, and Lechuguilla. Sulfuric acid not
only dissolves limestone, it leaves a distinctive chemical residue:
gypsum. This process, which is ongoing now in Cueva de Villa Luz,
was completed millions of years ago in Carlsbad and Lechuguilla,
where microbial activity continues today at a very slow pace.
Sulfuric acid is produced not just by snottites but also deep
underground in oil deposits. Microbes consume oil and release
hydrogen sulfide gas, which rises through rock fissures and combines
with groundwater to produce sulfuric acid.
To scientists, the biggest surprise is that this Earth-transforming
process is connected to life—especially life where no one
expected to find it, since caves were long considered virtually
sterile environments. Dubbed "extremophiles," these newfound organisms, living beyond the margin of what was
considered possible, are turning up in more and more environments,
from hot springs at Yellowstone National Park to volcanic vents at
the ocean bottom.
Some scientists believe these bacteria descend directly from the
earliest life forms that emerged on Earth some 3.5 billion years
ago. They may even be our best guess of what life is like on other
planets—buried beneath the surface of Mars, floating in the
oceans of Jupiter's moon Europa, and otherwise thriving in extreme
conditions throughout the cosmos.
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