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Scientists found samples of ocean crust that appeared to be altered by reactions with seawater at about 300°C—a sign of hydrothermal circulation. Pieces of highly altered rock (gray) are cemented
together with minerals such as iron sulfides (gold colored) and quartz
(white). This sample was recovered by drilling 116 meters below an active seafloor hydrothermal vent site at 26°N on the Mid-Atlantic Ridge. (Photo by Tom Kleindinst, WHOI) |