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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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