... Jupiter's moon Io. Other planets exhibit the results of volcanic activity. These include Mercury, the Earth's Moon, Jupiter's moon Europa, and perhaps Neptune's moon Triton. Planetary bodies, like Jupiter's moon Europa also exhibit icy volcanism where water takes the place of lava. Eruptions allow fresh gases to the surface from the melted material below. Volcanism is part of the process by which a planet cools off. Even though they are not volcano's, geysers and hot springs are also part of the volcanic process, involving water and hydrothermal activity. Much of the earth's surface especially the crust of the ocean floor consisted of very young rocks, geologically. The rocks came from long lines of volcanoes, which were located along ridges near centres of ocean basins, within the last 300 million years. When this was concluded the theory of plate tectonics was developed, this explained the locations and distributions of volcanoes on Earth. ...

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