This resource uses text and animation to depict the various processes that produce caves. For example, microbes feeding on the deadly gas hydrogen sulfide long ago excreted sulfuric acid that helped carve out Lechuguilla, Carlsbad. Geologists and microbiologists working in a still-growing Mexican cave provided the extraordinary evidence needed to convince skeptics. Other ways that caves form 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, the student can follow along as each of these four agents go about making caves.