It’s been estimated that in all of Earth’s history, there have been 7 supercontinents, with the most recent one being Pangaea.
The next supercontinent (Pangaea Ultima) is expected to form in around 250 million years.
Why is this the case? What phenomenon causes these giant landmasses to coalesce, break apart, then coalesce again?
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Convergent boundaries (subduction) create continental crust. Divergent boundaries (rifts) create oceanic crust.
With that in mind, on a sphere, with a long enough time scale, we tend to see oceans spread until the continental land masses end up more or less in the same area.
Also continental crust can be really really old. It sticks around for a long time despite erosion. It doesn’t readily subduct so it doesn’t get recycled like oceanic crust does. When continents collide they tend to get stuck together until they are eventually separated due to rifting, which sometimes leads to opening of a new ocean. At this point a new cycle begins.
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