Word: acidic
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Dates: during 1990-1999
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Caves can be pounded into existence by ocean waves, plowed open by ice or formed by lava. But to speleologists, the most interesting are those that have been etched out of limestone by acidic water flowing underground. For a long time, researchers believed that nature could accomplish this feat in only one way: through the action of carbonic acid, which is produced when water reacts with carbon dioxide. The weak acid slowly dissolves bedrock. An underground stream forms, and an elaborate network of chambers like those found at Mammoth Cave in Kentucky takes shape. The unusual limestone terrains where this...
Hill helped clear up the confusion in the 1980s by carefully measuring the sulfur content of samples taken from the caverns. Her work proved that Carlsbad was carved not by carbonic acid but by sulfuric acid, produced by a reaction between oxygen dissolved in groundwater and hydrogen sulfide bubbling up from deep below the earth's surface. This highly toxic solution, which would have killed anyone present at the time, sculpted the many subterranean chambers at Carlsbad...
...biology played an important role in the rock-dissolving process. By poring over slices of limestone under microscopes, scientists found the fossil remains of primitive bacteria that had thrived in the once hostile environment. Using sulfur instead of sunlight as their source of energy, these organisms actually bolstered the acid's power to etch rock. Descendants of these strange microbes have recently been found and are being studied at Lechuguilla Cave, not far from Carlsbad...
...attack. But the 91-year-old naval base earned a more dubious distinction last month when the Environmental Protection Agency (EPA) added the site to its list of the nation's most dangerously polluted places. Among the hazards scattered across 12,264 acres: unlined landfills, pesticide-disposal pits, chromic acid- disposal areas, heavy-metal contamination and waste-oil leakage...
...addition, the council discarded a proposed EPA ban on lead-acid automobile battery incineration, even though Health and Human Services Secretary Louis H. Sullivan said that lead is "the number one environmental threat to the health of children in the United States...