Teeming with weird and wonderful life--giant clams and mussels, tubeworms, "eyeless" shrimp, and bacteria that survive on sulfur--deep-sea hot-water springs are found along rifts where sea-floor spreading occurs. The theory of plate tectonics predicted the existence of these hydrothermal vents, but they were discovered only in 1977. Since then the sites have attracted teams of scientists seeking to understand how life can thrive in what would seem...