What is the ancient ocean that existed more than 200m years ago and surrounded the Pangea supercontinent?

Panthalassa, also known as the Panthalassic Ocean or Panthalassan Ocean (from Greek πᾶν "all" and θάλασσα "sea"), was the superocean that surrounded the supercontinent Pangaea. During the Paleozoic–Mesozoic transition c. 250 Ma it occupied almost 70% of Earth's surface.

Its ocean floor has 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 developed from its centre in the Mesozoic to the present.