2003-11-09 12:40:36 -- The life history of an ocean basin is determined by the balance between two opposing forces: sea floor spreading (rifting) and subduction. During the early phases of ocean formation, rifting dominates. A small continental rift, much like the East African Rift, grows wider forming a narrow ocean, like the Red Sea. Sea floor spreading continues to rapidly widen the ocean.
At some point in time a subduction zone forms along one of the margins of the ocean. Ocean floor is now destroyed at about the same rate that it is created. During this period in an ocean's history, it neither grows nor contracts, much like the modern Pacific.
Eventually the mid-ocean ridge gets too close to one of the margins and is subducted. Now the ocean is in a period of decline. Because no new ocean floor is being created, the ocean must close.
250 million years in the future, the Atlantic and Indian oceans have closed. North America has collided with Africa, but in a more southerly position than where it rifted. South America is wrapped around the southern tip of Africa, with Patagonia in contact with Indonesia, enclosing a remanent of the Indian Ocean.
Antarctica is once again at the South Pole and the Pacific has grown wider, encircling half the Earth.
We call this future Pangea, "Pangea Ultima", because it is the final Pangea.