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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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(Continued from page 2)

Preliminary results bowled over the researchers. “When we first came to Lower Kane,” says Summers Engel, “we naturally assumed that each mat would mainly consist of sulfur-oxidizing microbes. That seemed like common sense. What we found, instead, was astonishing complexity.” Each mat, in fact, turned out to be as diverse as a Manhattan city block. There were plenty of sulfur-eating microbes, all feeding off the gases bubbling up in the springs. But there was a riotous mix of other bacteria too. For example, some, oblivious to sulfur, were feeding off the waste generated by their neighbors. Nor were the bugs all thrown together at random. Sulfur-eating bacteria, for instance, congregated at the top of the mat; as greedy consumers of oxygen, they needed the air at the spring’s surface to survive. Methane producers that need no oxygen were concentrated, predictably, at the mat’s bottom.

To find out how the mats as a whole were affecting the cave, the scientists devised a test of elegant simplicity, involving two plastic tubes, each containing identical limestone chips. The mouth of one was covered with a crude plastic mesh, allowing both microbes and water from the spring to swirl inside. The other was covered with a membrane that admitted water but kept out the microbes. After submerging both tubes in the spring for several months, the team studied the chips under a microscope. The chip exposed to both the acidic water and the microbes was more severely pitted and scarred than the one exposed to water alone. Here was the proof that acid-producing microbes were accelerating the creation of the cave. “There’s no question that microbes are adding to the acid chemistry that’s dissolving the limestone,” says University of Texas geochemist Libby Stern, “and that without the mats Lower Kane probably would be forming at a much slower pace.”

But another find was even more tantalizing: a totally new species of microbe, tentatively identified by BrighamYoungUniversity biologist Megan Porter. The new organism appears closely related to microbes found at undersea vents deep in the Pacific, a likely point of origin for the emergence of life. “This is an exciting discovery,” says Porter, “because it implies that the types of metabolisms found in LowerKaneCave are very ancient.” It also fits with growing evidence that life may have begun in the depths. In subsurface havens like caves, undersea vents and in the soil, primitive microbes would have been sheltered from the volcanic blasts, meteor bombardments and intense ultraviolet radiation that made the planet so inhospitable in its early years. In these ancient refuges, which humans have only just figured out how to penetrate, life evolved far from sunlight, often in extreme conditions of heat and acidity. Kane’s psychedelic mats remind us how extraordinarily diverse and hardy earth’s ancient pioneers must have been.

But the horizons of cave research stretch far beyond our own planet. Many astronomers and geologists speculate that Jupiter’s moon Europa and Mars each harbor water and subsurface conditions resembling our own. If microbes can survive in harsh conditions here, why not there as well? “Our work in caves has broadened the known limits of life on our own planet,” says Penny Boston. “But it’s also a great dress rehearsal for studying biological sites on other planets, and pushing our imaginations to connect earth’s ‘inner-terrestrials’ with those of outer space.”

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