Panthalassa

thumb|upright=1.3|The Panthalassa superocean 250 million years ago thumb|upright=1.3|The supercontinent Pangaea in the early Mesozoic (at 200 Ma) surrounded by Panthalassa. thumb|upright=1.3|The Pacific Plate began forming when the [[triple junction at the center of Panthalassa destabilized about 190 million years ago.]] Panthalassa, also known as the Panthalassic Ocean or Panthalassan Ocean (from Greek "all" and "sea"), was the vast superocean that encompassed planet Earth and surrounded the supercontinent Pangaea, the latest in a series of supercontinents in the history of Earth. During the Paleozoic–Mesozoic transition ( 250 ), the ocean occupied almost 70% of Earth's surface, with the supercontinent Pangaea taking up the remaining one third. The original, ancient ocean floor has now completely disappeared because of the continuous subduction along the continental margins on its circumference. Panthalassa is also referred to as the Paleo-Pacific ("old Pacific") or Proto-Pacific because the Pacific Ocean is a direct continuation of Panthalassa.

==Formation== The supercontinent Rodinia began to break up 870–845  probably as a consequence of a superplume caused by mantle slab avalanches along the margins of the supercontinent. In a second episode 750  the western half of Rodinia started to rift apart: western Kalahari and South China broke away from the western margins of Laurentia; and by 720  Australia and East Antarctica had also separated. In the Early Jurassic the Pacific Plate opened originating from a triple junction between the Panthalassic Farallon, Phoenix, and Izanagi plates. Panthalassa can be reconstructed based on magnetic lineations and fracture zones preserved in the western Pacific.