In 1991, scientists aboard the submersible Alvin were in the right spot at the right time to witness something extraordinary. They had sailed into the aftermath of a very recent volcanic eruption on the seafloor and found themselves in a virtual blizzard. They were densely surrounded by flocs of white debris, composed of sulfur and microbes, which drifted more than 30 meters above the ocean bottom. The seafloor was coated with a 10-centimeter-thick layer of the same white material. This vast volume of microbes did not come from the ocean. The eruption had flushed it out from beneath the seafloor.