In 1977, scientists diving in the submersible Alvin on the Galapagos Ridge made a fantastic discovery: springs of warm water emerging from the ocean floor where water temperatures are near freezing, and an abundance of life in what was previously considered a desert. Two years later, predictions they made from the Galapagos dives led them to an even more amazing sight. On the East Pacific Rise off the coast of Mexico, more than a mile and a half below the ocean surface, hot springs exited the ocean floor at more than 350°C — hot enough to melt lead — spewing what looked like black smoke from “chimneys” composed of glittering minerals. Fantastic new life forms were discovered at these vents, in an ecosystem that seemed to be completely independent of photosynthesis at the Earth’s surface. Over twenty years later, we know these hydrothermal vents to occur all along the length of the mid-ocean ridge, a globe-encircling volcanic mountain chain that marks where the Earth’s tectonic plates move apart. In this lecture we will cover the story of exploration of the seafloor and the discovery of hydrothermal vents, what we know of them today, and some of the fascinating questions that remain.