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Subterranean Surprises

Scientists are discovering that caves more complex than we ever imagined may yield vast riches about the origins of life

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A few miles south of Lovell, Wyoming, near the Montana border, the Burlington Northern railroad begins a gradual climb out of pastures and cottonwood groves. The track rises into a honey-colored gorge cut through Madison limestone, a formation already ancient by the time dinosaurs roamed Wyoming’s seashores, then passes above an underground chamber, 30 feet below, known as Lower Kane Cave. The cave entrance is nearly invisible, a crack almost buried by the steeply piled rubble of the railway embankment.

Stumbling down this ankle-twisting slope behind a team of scientists, I squirmed feetfirst through the 30-inch crack. Bent double and fumbling my way forward in the gloom, I slipped into a fast-moving stream and floundered on all fours before finding enough room to stand upright on the mud bank. My eyes soon adjusted to the dim glow of my headlamp, but my skin remained sticky; unlike most caves at this latitude that stay pleasantly cool year-round, the temperature in Lower Kane hovers at an uncomfortably humid 75 degrees. An acrid, rotten smell stuck in my throat.

Lower Kane has none of the sparkling columns or limestone “draperies” of subterranean tourist spots such as New Mexico’s Carlsbad Caverns or Kentucky’s MammothCave. Scarcely larger than a typical New York City subway station, Lower Kane lacks even the humblest stalactite. Yet this unprepossessing cave is proving to be a scientific gold mine, drawing to its humid depths an energetic group of researchers, led by Annette Summers Engel of the University of Texas. Wearing safety masks to guard against toxic gases that bubble up from three spring-fed pools, the team is pursuing the latest chapter in a 30-year effort to understand the rare and exotic form of cave that Kane represents; only about a dozen of these so-called active sulfide caves have been found worldwide. When first proposed in the early 1970s, the theory of their origins was so controversial that the scientific community took nearly two decades to embrace it. Eventually, the unusual geochemistry of these caves overturned conventional thinking about how they were formed.

More significantly, the discovery of “dark life”—teeming colonies of microbes thriving in these acid-drenched, pitch-black netherworlds—has thrown out a long-held belief that caves are mostly barren and sterile places. Scientists are hunting in these once-hidden depths for microbes that may lead to new cancer treatments. And cave research is also affecting scientists’ thinking about the origins of life on earth and its possible existence on other worlds. “A cave is such a different environment, it’s almost like going to another planet,” says New Mexico Tech geomicrobiologist Penny Boston. “In a sense, it is another planet—the part of our own planet that we haven’t explored yet. Just as the deep oceans became accessible to science only in the past few decades, now we’re finding that kind of pioneering effort going on in caves.” (A television exploration of cave research, “Mysterious Life of Caves,” airs on PBS’s NOVA October 1.)

In the late ’60s, a StanfordUniversity graduate student searching for a challenging topic for his PhD thesis became the first scientist to squeeze through the crack in the Wyoming railway embankment. Stephen Egemeier’s curiosity was immediately aroused by Lower Kane’s unusually warm temperatures and unpleasant smells. Even stranger were the huge, muddy heaps of a crumbly white mineral rarely found in caves. This was gypsum, or calcium sulfate, the main ingredient in Sheetrock or drywall, the material familiar from house construction. When Egemeier discovered that Lower Kane’s springs were not only hot but were bubbling hydrogen sulfide gas (notorious for its rottenegg smell), he theorized that hydrogen sulfide was actively at work in carving out Lower Kane. Whatever underground source the potentially toxic gas ultimately came from—whether the volcanic reservoirs of Yellowstone to the west or the oil fields of the BighornBasin to the south—it was bubbling out of the springwater and into the cave. Naturally unstable, it was reacting with oxygen in the water to form sulfuric acid. The acid was eating away at the cave walls and producing gypsum as a by-product.

Egemeier’s pioneering research was never widely published and attracted little attention in the ’70s. But while it languished, another group of scientists was grappling with some equally puzzling cave riddles. This time, the scientific detective hunt unfolded far from Wyoming’s rugged canyons in the well-trampled depths of a major tourist destination, Carlsbad Caverns.

The early carlsbad story is essentially the story of a single individual, Jim White. As a teenager in the 1890s, White was wandering near his campsite in the GuadalupeMountains of southeastern New Mexico when he spotted a strange dark cloud swirling up from the desert floor. “I thought it was a volcano,” he said later, “but then I’d never seen a volcano.” Tracing the cloud to its origin at the mouth of a gigantic cavern, White stood transfixed by the spectacle of millions of bats pouring out on their nightly hunting exodus. So began his lifelong obsession with Carlsbad Caverns, which he generally explored alone, with only the feeble flicker of a kerosene lamp to guide him. White’s tales of a vast underground labyrinth made him something of a local laughingstock until he persuaded a photographer to accompany him into the cave in 1915. In the months that followed, White would lower visitors in an iron bucket on a wobbly winch into the darkness 170 feet below. Today, of course, his solitary obsession has become a national park drawing half a million visitors a year.

But perhaps the most surprising aspect of the Carlsbad story is that even as late as the 1970s, when daily summer visitors numbered in the thousands, the caverns’ mineralogy and its many puzzling features had hardly been studied. Speleology, or the study of caves, was barely a respectable science, and according to cave expert Carol Hill, mainstream geologists tended to dismiss as “grubby cavers” those who were attracted to the subject.

Then, one day in October 1971, Hill and three other young geology graduate students climbed a steep ladder into one of Carlsbad’s remote chambers. As they clambered about the Mystery Room, named for the strange noise made by wind there, they were baffled by patches of bluish clay at their feet and crumbly, cornflake-like crusts on the walls. Odder still were the massive blocks of a soft, white mineral elsewhere in the cave. Such blocks shouldn’t have been there at all.

For one thing, this mineral, gypsum, quickly dissolves in water. And the conventional explanation of how caves are formed involves the action of water—lots of it—percolating through limestone over millions of years. The chemistry is simple: as rain falls through the atmosphere and trickles into the soil, it picks up carbon dioxide and forms a weak acidic solution, carbonic acid. This mildly corrosive groundwater eats away the limestone and, over eons, etches out a cave.

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