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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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According to this universally accepted theory, all limestone caves should consist of long, narrow corridors. Yet as anyone who has trekked through Carlsbad’s main attraction, the Big Room, knows, it is a gigantic, cathedral-like hall extending over the equivalent of six football fields. Had a major underground river carved out this immense cavern, it should have eroded or swept aside everything in its path, including gypsum. Yet giant white heaps of the stuff up to 15 feet thick lie on the floor of the Big Room, one of the largest cave spaces in the world.

Puzzled, Hill was forced to conclude that some drastically different method of cave formation must have been at work in the GuadalupeMountains. Soon she came up with a theory similar to Egemeier’s: that hydrogen sulfide given off by nearby oil and gas fields had risen up through the mountains and reacted with oxygen in groundwater to produce sulfuric acid, which had then eaten away the caves over millions of years.

Her hydrogen sulfide theory aroused intense skepticism among geologists, who sought proof, which Carlsbad, as a “dead” or no longer forming cavern, could not provide. To confirm Hill’s theory, scientists needed to investigate a site where sulfuric acid was still eating away at the cave—as it was at Lower Kane. But over the years the little cave under the railway track had been more or less forgotten.

In 1987, Hill’s meticulous study of the Guadalupes at last appeared, coinciding with the publication of Stephen Egemeier’s work after his death in 1985. These studies, along with new discoveries of a handful of other active sulfide caves around the world, proved beyond any doubt that caves in some regions were formed by sulfuric acid. But now a more tantalizing question arose: How could life thrive inside pitch-dark caverns full of toxic gas?

One of my spookiest moments visiting Lower Kane was when I aimed my flashlight beam at one of the cave’s three pools. Just below the water’s surface stretched a crazy pattern of stringy, filmy matting in startling shades of blue-black, vermilion and garish Day-Glo orange, as if some 1960s pop artist had tossed paint in every direction. In some places, the mottled, pitted orange patterns reminded me of NASA images of the barren surface of Mars. In others, it looked as if someone had dumped spaghetti sauce in the water. And floating in the water directly over each spring, spidery white filaments, like delicate cobwebs, performed a ghostly underwater dance in the currents bubbling up from below.

The psychedelic colors all belonged to bacterial mats, gelatinous films of carbon compounds generated by invisible microbes. These vivid by-products of bacterial activity can be seen clustering around hot springs in Yellowstone and elsewhere, though on the surface they can be overwhelmed by competition from algae and other organisms. But what were they doing here in Lower Kane, thriving so abundantly in a place with poisonous gases and no sunlight?

For most of the 20th century, scientists believed no bacteria could exist more than a few yards beneath topsoil or ocean mud; below that, scientists thought, life simply fizzled out. Then, in 1977, came the astonishing discovery of bizarre tube worms and other exotic animals, all huddled around submerged volcanoes so deep in the Pacific that sunlight does not reach them. This otherworldly ecosystem turned out to depend almost entirely on the activity of sulfur-loving bacteria, thriving on the scalding currents and gases released by undersea vents. Equally startling revelations about microbes in other unlikely places soon followed: bacteria were found in cores drilled more than a mile below Virginia, inside rocks from inhospitable Antarctica, and more than six miles deep in the Pacific at the bottom of the Marianas Trench. Some scientists now speculate that hidden subsurface bacteria may equal the mass of all living material above.

This “dark life,” isolated for billions of years, opens up tantalizing prospects for scientists. Microbiologists hope that underground bacteria can lead to new antibiotics or anticancer agents. NASA specialists are investigating them in hopes of identifying signatures that they might recognize in rock samples from Mars or in probes that may one day penetrate the frozen seas of Europa, one of Jupiter’s moons.

But the challenge for all these hunters of subterranean bugs is access, which is where Lower Kane comes in. “Caves offer a perfect walk-in window to the normally hidden world of microbial activity,” says Diana Northup, a cave investigator at the University of New Mexico. “Some researchers speculate that life evolved first underground and moved to the surface as conditions improved. If this is true, then studies of subsurface microbes may offer clues to the nature of some of earth’s earliest life-forms.”

Although LowerKaneCave had given me a soaking and a bruise or two, my discomforts were nothing compared with the miles of wriggling and squeezing required to penetrate many other sulfide caves. Its accessibility was one reason Lower Kane attracted Annette Summers Engel first in 1999 and every year since, allowing her and her team of geologists, geochemists and DNA experts to haul scientific equipment in and out with relative ease. Their initial tests quickly confirmed that Stephen Egemeier had been right: sulfuric acid, the result of hydrogen sulfide reacting with oxygen, was indeed still eating away the cave walls. The most intriguing question was whether Lower Kane’s bacterial mats were adding to the acid attack. Since some bacteria produce sulfuric acid as waste products, it certainly seemed possible. Summers Engel’s plan was to tackle the question from several different angles. A DNA test, for example, might identify particular microbes. Other tests might tell whether a microbe fed on, say, sulfur or iron, and whether it was stressed or flourishing.

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