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- We know that new plate material is being formed
- and these lithospheric plates on the surface of the earth
- are moving around,
- and that might raise the question in your brain,
- "What happens if we kind of reverse things?
- We know the direction that they're moving in;
- what does that tell us about where they came from?"
- So let's just do the thought experiment.
- Right now South America and Africa are moving away from each other
- because of new plate material being created
- at the Mid-Atlantic Rift.
- Let's rewind it.
- Let's bring them back together.
- We know that India is jamming into the Eurasian plate right now,
- causing the Himalayas to get higher and higher.
- What if we rewind that?
- Let's bring India back down towards Antarctica.
- Same thing with Australia.
- We have new plate material being formed between Australia and Antarctica,
- that's making the continents move apart.
- Let's bring them back together.
- Let's rewind the clock.
- Even North America — it's not as obvious from this diagram
- but if you look at the GPS data, it's pretty obvious
- that North America right now is kind of
- moving in a counterclockwise rotation.
- So let's rewind it. Let's rewind it into a —
- let's go back, moving it in a clockwise direction.
- Instead of Eurasia going further away from North America,
- let's bring it back together.
- So what you can imagine is a reality where
- India and Australia are jammed down into Antarctica,
- South America and Africa are jammed together,
- North America is jammed in there,
- and essentially Eurasia's also jammed in there.
- So it looks like they're all kind of clumped together
- if you go back a few hundred million years.
- And, based on literally just that thought experiment,
- you can imagine that at one point,
- all of the continents on the world
- were kind of merged into one supercontinent.
- And that supercontinent is called "Pangaea."
- "Pan-" for "entire" or "whole,"
- and "-gaea," coming from "Gaia," for "the world."
- And it turns out that all of the evidence that we've seen
- actually does make us believe
- that there was supercontinent called —
- well, we call it Pangaea now, obviously
- there weren't things on the planet
- calling it anything back then,
- well, there were things back then,
- but not things that would actually go and try to label continents,
- that we know of,
- but all of the evidence tells us that Pangaea existed
- about 200 million to 300 million years ago —
- roughly maybe 250 million, give or take, years ago.
- And I want to be clear, this was not the first supercontinent.
- To a large degree, it was the most recent supercontinent,
- it's easiest for us to construct because it was the most recent one,
- but we believe that there were other supercontinents before this.
- if you rewind even more,
- you would have to break up Pangaea and it would reform
- but we're now going back in time.
- But there were several supercontinents in the past
- that broke up, reformed, broke up, reformed,
- and the last time that we had a supercontinent
- was Pangaea, about 250 million years ago.
- And now it's broken up into our current-day geography.
- Now, I won't go into all of the detail why we believe
- that there was a Pangaea about 250 million years ago,
- or this diagram tells us, about 225 million year ago,
- give or take.
- But I'll go into some of the interesting evidence.
- On a very high level, you have a lot of rock commonalities
- between things that would have had to combine during Pangaea.
- And probably the most interesting thing is the fossil evidence.
- There's a whole bunch of fossils,
- and here's examples of it.
- From species that were around between 200 and 300 million years ago.
- And their fossils are found in a very specific place.
- This animal right here, Cynognathus
- — I hope I'm pronouncing that right —
- Cynognathus, this animal's fossils are only found
- in this area of South America, the nice clean band here,
- and this part of Africa.
- So not only does South America look like it fits very nicely
- into Africa,
- but the fossil evidence also makes it look like
- there was a nice clean band where this animal lived
- and where we find the fossils.
- It really makes it seem like these were connected,
- at least when this animal lived.
- Maybe on the order of 250 million years ago.
- This species right over here,
- its fossils are found in this area.
- Let me do it in a color that has more contrast —
- in this area right over here.
- This plant, its fossils
- — now this starts to connect a lot of dots between a lot of continents —
- its fossils are found in this entire area,
- across South America, Africa, Antarctica, India, and Australia.
- And so not only does it look like
- the continents kind of fit together in a puzzle piece,
- not only do we get it to a configuration like this
- if we essentially just rewind the movement that we're seeing now,
- but the fossil evidence also kind of confirms
- that they fit together in this way.
- This animal right here,
- we find fossils on this nice stripe that goes
- from Africa through India all the way to Antarctica.
- Now this only gives us evidence of
- kind of the more, the Southern Hemisphere of Pangaea.
- But there is other evidence.
- We find continuing mountain chains between North America and Europe.
- We find rock evidence where,
- just the way you see fossils that line up nicely,
- we see common rock that lines up nicely
- between South American and Africa
- and other continents that were at once connected.
- So all of the evidence so far as we can tell now
- does make us think that there was at one time a Pangaea.
- And, for all we know, all the continents are going to keep moving,
- and maybe, in a few hundred million years,
- we'll have another supercontinent. Who knows.