We know that new plate
material is being formed, and these lithosphere 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
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 actually
look at the GPS data, it becomes pretty obvious
that North America, right now is moving in a
counterclockwise rotation. So let's rewind it
into a-- let's go back, moving it in a
clockwise direction. Let's, instead of Eurasia
going further away from North America, let's
bring it back together. And so what you could
imagine is a reality where India, Australia
are jammed down into South America--
sorry, into Antarctica. South America and Africa
are jammed together. North America is
jammed in there. And essentially, Eurasia
is also jammed in there. So it looks like they
all would clump together if you go back a few
hundred million years. And based on, literally--
based on just that thought experiment, you could
imagine at one point, all of the continents
on the world were 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 we've seen actually does make us believe that there
was a supercontinent called-- well, we call it Pangaea, now. Obviously, there
probably weren't things on the planet calling
it anything back then. Or, 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 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's kind of
the most recent supercontinent. And it's easiest
for us to construct because it was the
most recent one. But we believe that there
were other supercontinents before this. That if you rewind
even more that you would have to break up
Pangaea and it would reform. But we're now
going back in time. Or that there were
several supercontinents in the past that broke up,
reformed, broke up, reformed. And the last time 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 years 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 are a whole
bunch of fossils. And here are 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 on a nice clean band here, and in 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. So 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 to a lot of
dots between a lot of cont-- 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 fit together in a puzzle
piece, not only do we get it to a
configuration like this if we essentially just
rewind to 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 the Southern Hemisphere of Pangaea. But there is other evidence. We find kind of
continuing mountain chains between North
America and Europe. We find rock evidence,
where just the way we see the fossils
line up nicely. We see common rock that lines
up nicely between South America and Africa and other continents
that were at once connected. So all the evidence, as
far as we can tell now, does make us think that there
at one time was 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?