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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Plate tectonics. Imagine that you have a pan full of sandy mud, some gravel and some fairly big stones. If you just randomly swish them all around in the pan they’re going to clump up then if you shake the pan some more they’re going to eventually break apart and swish around again for a while until they clump up again in a different way. That’s what the continents do, just in a much slower more natural and beautifully balanced way.
The tectonic plates are moving around all the time. They’re pretty big, so they bump into each other a lot, if you wait long enough.
Whether they happen to form a supercontinent isn’t really significant except for our perception. The entire surface of the planet is covered in tectonic plates, we only think the ones that poke up higher than sea level are important because we can live on them. When the land is connected, we notice. When the land isn’t connected, we notice. There’s no geological reason to prefer either configuration, as far as I know
We actually don’t know. Well, we know how statistics works and whatnot, and that’s sort of why, but we actually don’t know the mechanism. There is a simplified version though that I’ll try to give her, but just know that this is not rooted in theory, it’s more of a hypothesis that we have.
Take a sphere, and put two panels on it, next to each other. These are your continental plates for this experiment. Now for each one, pick a direction, and start moving it. Eventually they will hit each other again. It does not matter which directions or speeds you choose, eventually they will hit. Alternatively, take those plates, move them away half a sphere, and then have them follow the same path back. Of course they will hit again. These two mechanisms are the statistics of why plate tectonics will produce super continents: eventually it’ll all end up together again anyways.
The problem is that this explains that it happens, but not why it happens. We just don’t know why it happens as often as it has on earth, and it could simply be coincidence, but scientists don’t like that as an explanation. There could also be an underlying mechanism regarding the viscosity of the mantle or the angular velocity of the earth or Cthulhu just moving around pieces like a toddler playing with cars or something we don’t know really. It is interesting to not that we thought we knew, but then, we found out that the super continents may have formed differently than we thought they did.
The chunks of crust that makes continents is kind of like ice cubes floating on water, but made out of the lightest kinds of rocks, and they’re floating on hot magma.
The chunks of crust under the oceans are similar, but made of heavier kinds of rock.
When continents bump into oceans, the continental crust usually goes on top of the ocean crust and it sinks back into the mantle.
When two continents bump into each other, both are too light to go down into the mantle, so they crunch up and make big mountains and get stuck together.
This happens over and over until all of the continents make one big continent.
And because the mantle is basically “boiling” all the time, hot spots (like bubbles of steam, but made of melted rock called magma) form randomly under the crust. The heat has to go somewhere, so it cracks the crust open and forces the big continent to break back apart.
This happens over and over over hundreds of millions of years.
Because the earth is a sphere and things can only get so far apart before any further movement apart just makes them closer together in the opposite hemisphere.
Follow up question, will the landmasses break apart differently next time around? And IF countries still exists, will we have to fight over territories again?
If you want a more nuanced answer than just “that’s what they do” I’ll do my best.
So plate tectonics is driven by multiple sources of energy. When rifting occurs it “pushes” the plates away from spreading centers and when subduction occurs it “pulls” the oceanic plates and all of this energy is driven indirectly by convection cells in the mantle. Some of the statements I just gave you are simplifications and/or up for debate.
But based on what tectonic regimes are at play globally, the continents tend to be pushed together when continental rifting occurs less and subduction zones occur more often. Why these paradigms change is a much more complex conversation.
The geometry of a sphere that the continental plates are essentially floating across they are bound to collide given enough time, just kinda a statistics thing. Or like when you take two strings and jostle them around in a box they become tangled and knitted.
When continental rifting happens at accelerated rates the continents tend to diverge.
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.
Think about the earth as a sphere from molten stone,
where hot molten material from the depth raises to the surface,
this convection pushes the floating continents away,
on a sphere where the floating pieces
are much smaller than the surface of the sphere,
this pieces are moved to each other,
because the convection force between them is lower that the force around them,
than the supercontinent is build.
Next now the force still presses around this supercontinent,
but it is formed from pieces and so on piece is forcly moved pressed under an other,
thing like the alps or the himalaya happens,
and things like the mariana trench as the opposite,
this forces than build up to break everything apart again
and so the circle continuous.
I hope i did it but this is hardcore in ELI5.
Imagine you have a bunch of floating pool toys. Sometimes the current of the filter clumps them all together, sometimes they break apart and float around. The continents are on tectonic plates that act very similarly, although instead of pool water it’s liquid hot magma.
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