Beneath the surface of our own world lies a realm more foreign to human knowledge than the face of Mars — a darkness where, in 1977, a submersible named Alvin encountered life thriving without sunlight, rewriting the oldest assumption in biology. The discovery that microbes could draw energy from volcanic chemistry rather than solar light did not merely expand a textbook; it reopened the question of where, in the universe, life might be possible. We have mapped less than a third of our ocean floor, yet we now look outward to ice-covered moons with new eyes, carrying a lesson learned in the dee