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Panthalassa, also known as the Panthalassic or Panthalassan Ocean, (from Greek Ïá¾¶Î½ all and Î¸Î¬Î»Î±ÏÏÎ± sea), was the superocean that surrounded the supercontinent Pangaea. During the PaleozoicâMesozoic transition c. 250 Ma it occupied almost 70% of Earth's surface.
Plates surround the Pacific Ocean. The Pacific Plate is surrounded by large and small crustal plates. These tectonic plate boundaries are the reason that of the 1,500 volcanoes that have been active in historic time and 90 percent of them occur in the Pacific Ocean.