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We know that new plate material is being formed

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and these lithospheric plates on the surface of the earth

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are moving around,

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and that might raise the question in your brain,

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"What happens if we kind of reverse things?

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We know the direction that they're moving in;

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what does that tell us about where they came from?"

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So let's just do the thought experiment.

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Right now South America and Africa are moving away from each other

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because of new plate material being created

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at the Mid-Atlantic Rift.

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Let's rewind it.

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Let's bring them back together.

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We know that India is jamming into the Eurasian plate right now,

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causing the Himalayas to get higher and higher.

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What if we rewind that?

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Let's bring India back down towards Antarctica.

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Same thing with Australia.

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We have new plate material being formed between Australia and Antarctica,

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that's making the continents move apart.

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Let's bring them back together.

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Let's rewind the clock.

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Even North America — it's not as obvious from this diagram

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but if you look at the GPS data, it's pretty obvious

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that North America right now is kind of

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moving in a counterclockwise rotation.

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So let's rewind it. Let's rewind it into a —

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let's go back, moving it in a clockwise direction.

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Instead of Eurasia going further away from North America,

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let's bring it back together.

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So what you can imagine is a reality where

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India and Australia are jammed down into Antarctica,

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South America and Africa are jammed together,

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North America is jammed in there,

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and essentially Eurasia's also jammed in there.

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So it looks like they're all kind of clumped together

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if you go back a few hundred million years.

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And, based on literally just that thought experiment,

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you can imagine that at one point,

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all of the continents on the world

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were kind of merged into one supercontinent.

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And that supercontinent is called "Pangaea."

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"Pan-" for "entire" or "whole,"

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and "-gaea," coming from "Gaia," for "the world."

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And it turns out that all of the evidence that we've seen

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actually does make us believe

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that there was supercontinent called —

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well, we call it Pangaea now, obviously

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there weren't things on the planet

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calling it anything back then,

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well, there were things back then,

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but not things that would actually go and try to label continents,

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that we know of,

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but all of the evidence tells us that Pangaea existed

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about 200 million to 300 million years ago —

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roughly maybe 250 million, give or take, years ago.

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And I want to be clear, this was not the first supercontinent.

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To a large degree, it was the most recent supercontinent,

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it's easiest for us to construct because it was the most recent one,

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but we believe that there were other supercontinents before this.

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if you rewind even more,

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you would have to break up Pangaea and it would reform

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but we're now going back in time.

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But there were several supercontinents in the past

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that broke up, reformed, broke up, reformed,

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and the last time that we had a supercontinent

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was Pangaea, about 250 million years ago.

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And now it's broken up into our current-day geography.

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Now, I won't go into all of the detail why we believe

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that there was a Pangaea about 250 million years ago,

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or this diagram tells us, about 225 million year ago,

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give or take.

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But I'll go into some of the interesting evidence.

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On a very high level, you have a lot of rock commonalities

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between things that would have had to combine during Pangaea.

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And probably the most interesting thing is the fossil evidence.

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There's a whole bunch of fossils,

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and here's examples of it.

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From species that were around between 200 and 300 million years ago.

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And their fossils are found in a very specific place.

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This animal right here, Cynognathus

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— I hope I'm pronouncing that right —

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Cynognathus, this animal's fossils are only found

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in this area of South America, the nice clean band here,

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and this part of Africa.

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So not only does South America look like it fits very nicely

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into Africa,

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but the fossil evidence also makes it look like

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there was a nice clean band where this animal lived

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and where we find the fossils.

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It really makes it seem like these were connected,

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at least when this animal lived.

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Maybe on the order of 250 million years ago.

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This species right over here,

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its fossils are found in this area.

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Let me do it in a color that has more contrast —

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in this area right over here.

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This plant, its fossils

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— now this starts to connect a lot of dots between a lot of continents —

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its fossils are found in this entire area,

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across South America, Africa, Antarctica, India, and Australia.

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And so not only does it look like

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the continents kind of fit together in a puzzle piece,

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not only do we get it to a configuration like this

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if we essentially just rewind the movement that we're seeing now,

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but the fossil evidence also kind of confirms

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that they fit together in this way.

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This animal right here,

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we find fossils on this nice stripe that goes

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from Africa through India all the way to Antarctica.

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Now this only gives us evidence of

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kind of the more, the Southern Hemisphere of Pangaea.

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But there is other evidence.

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We find continuing mountain chains between North America and Europe.

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We find rock evidence where,

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just the way you see fossils that line up nicely,

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we see common rock that lines up nicely

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between South American and Africa

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and other continents that were at once connected.

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So all of the evidence so far as we can tell now

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does make us think that there was at one time a Pangaea.

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And, for all we know, all the continents are going to keep moving,

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and maybe, in a few hundred million years,

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we'll have another supercontinent. Who knows.