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Deep beneath the ocean surface, far from any sunlight, entire communities thrive around hydrothermal vents, cracks where superheated, mineral-rich water gushes from the seafloor. With no light for photosynthesis, the base of this food web is built instead by bacteria that draw energy from chemicals in the vent fluid, a process called chemosynthesis. Tube worms, clams, and shrimp depend on these microbes, some hosting them directly inside their bodies. The discovery of such ecosystems in the 1970s startled biologists, who had assumed sunlight was the ultimate source of energy for nearly all life on Earth.