National Geographic : 1988 Feb
D The mountain range nobody sees The largest mountain range on this planet is not the Himalayas, the Andes, or the Rockies. It is larger than those three combined. Concealed from view on the bottom of the seas, the Mid-Ocean Ridge winds around the globe for 74,000 kilometers (46,000 miles). It boasts higher mountains, deeper canyons, and longer escarpments than anywhere on the surface of the continents. Along the crest of the system fissures mark the boundary between the great plates that form earth's crust. These cracks are the birthplace - of new seafloor. Hot lava erupts and welds to each side of the separating plates. For more than 40 years Scientific expeditions, some sponsored by National Geographic Society, have focused on the Mid-Atlantic Ridge (drawing), the most Shrugged section of the system. Here crustal plates carrying North America, Africa, and Europe separate at the rate of three centimeters (an inch) a year. In the 1970s French and American scientists descended in the deep submersible Alvin for the first S closeup look at the ridge. Among them was Dr. Robert D. Ballard, who has since participated in other breakthrough studies of the Mid Ocean Ridge. These explorations have discovered unique chemical-laden hot water vents that support life with bacteria, not sunlight. Dr. Ballard and his associates now believe the ridge is not a simple seam but is made up of spreading cells, each with varying amounts of activity. The ridge is offset by faults running across its axis. "In many ways the ocean floor is more hostile and strange than the moon," Ballard says. "You can walk S around the moon's surface. Down in '*,_ the ocean it's totally dark. The * - temperature is nearly freezing, and the pressure outside our submersible is tremendous. So, in a way, when we dive into inner space, we travel to another planet."