Black smoker from the mid-Atlantic Ridge -- These dark, billowing clouds of hot hydrothermal fluid are rich in dissolved metals. As they rise into the cool ocean water, they precipitate these metals along the sides of the vent, thus creating a "chimney" that builds over time. The fluids also provide nutrients to a variety of unusual plants and animals that congregate around the vents in an area of the ocean where life would generally not exist. Courtesy of Peter Rona, NOAA.