Born in the Dark The Strange Biology of Life at Hydrothermal Vents

For most of the twentieth century, the deep ocean was where biology was supposed to run out. The reasoning was simple and seemed airtight. Nearly every living thing people had ever studied ran, directly or indirectly, on sunlight. Plants and algae capture it. Grazers eat the plants, predators eat the grazers, and the energy passes along the chain. Below a few hundred meters, the light fades to nothing. Below a kilometer, the water is near freezing, and the pressure is enough to crush a submarine built carelessly. Whatever lived down there, the thinking went, was a thin scattering of scavengers living off the slow drizzle of dead plankton from above. The deep seafloor was a desert.

Then a few geologists went looking for something that had nothing to do with life. For years, scientists had suspected that seawater must seep down through cracks in the young volcanic crust where tectonic plates pull apart. There it would be heated by the molten rock below and rise again, carrying dissolved minerals. The theory made sense of puzzling gaps in the ocean's chemical budget, but nobody had ever seen such a spring. In 1976, a towed camera and temperature sensors passed over a stretch of the Galápagos Rift in the eastern Pacific and picked up strange warm spots in the near-freezing water. Something down there was giving off heat.

So the expedition came back in 1977, aboard the research ship Knorr, carrying the little submersible Alvin. Alvin was a sturdy, cramped sphere about the size of a walk-in closet, built to carry a pilot and two scientists. Three people squeezed inside, sealed the hatch, and sank about 7,500 feet, more than two kilometers, down into the dark.