Three miles (five kilometers) below the surface of the Caribbean Sea (map), great volcanic chimneys gush subterranean water hot enough to melt lead. Found via robotic submersibles on April 6, these two-story-tall "black smokers" are the world's deepest known hydrothermal vents, scientists announced from aboard a research ship Sunday. "It was like wandering across the surface of another world," geochemist Bramley Murton, speaking in a press statement, said of steering a submersible around the record-breaking volcanic vents. "The rainbow hues of the mineral spires and the fluorescent blues of the microbial mats covering them were like nothing I had ever...