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
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,
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