Panthalassa (Greek  "all" and "ocean"), also known as the Panthalassic Ocean, was the vast global ancestral Pacific ocean that surrounded the supercontinent Pangaea, during the late Paleozoic and the early Mesozoic eras. It included the Pacific Ocean to the west and north and the Tethys Ocean to the southeast. It became the Pacific Ocean, following the closing of the Tethys basin and the breakup of Pangaea, which created the Atlantic, Arctic, and Indian Ocean basins. The Panthalassic is often called the Paleo-Pacific ("old Pacific") because the Pacific Ocean developed from it in the Mesozoic to the present.