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"Extraordinary claims require extraordinary evidence." This dictum from Carl Sagan applies quite well to the recent claim, as chronicled in NOVA's "Mysterious Life of Caves," that microbes feeding on the deadly gas hydrogen sulfide long ago excreted sulfuric acid that helped carve out Lechuguilla, Carlsbad, and other otherworldly caverns. Bacteria dissolving rock? The idea seemed absurd, until geologists and microbiologists working in a still-growing Mexican cave provided the "extraordinary evidence" needed to convince skeptics.
As remarkable as this process is, it is only the most unusual of several principal ways that caves form. Other ways include mildly acidic rainwater eating away limestone caverns, ocean waves scouring out sea caves, and lava forming long tunnels called lava tubes. In this feature, follow along as each of these four agents go about making caves.
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Flash is a plug-in that allows for increased interactivity. If you can see
the animated boxes at left, the plugin is already installed. If you do not see
the boxes, you can install the Flash plugin, or select this feature's
non-Flash version.
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