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Our continents and oceans might seem like they’ve been around forever,
but when you look at Earth’s 4.5-billion-year history,
they’re actually pretty new.
Like, until only about 180 million years ago, all the major landmasses
were clumped together in a giant supercontinent called Pangea.
So, not too long ago, Earth was a planet that would look
totally unfamiliar to us.
But Pangea wasn’t the first supercontinent, and it won’t be the last.
Geologists have spent decades modeling supercontinents using
evidence from around the world, and they’ve learned that
we have another one coming in 200 million years or so.
Except... no one is quite sure what it’ll look like,
or where it’ll even be.
And the answer depends on what happens inside the Earth.
For context: Supercontinents form and break up because Earth’s crust
and a tiny bit of its mantle are broken into pieces.
They’re called tectonic plates, and they move around the planet,
carried by currents in the mantle below.
Geologists have studied plates and how they move with everything
from lasers to rock formations to fossils to quasars in space.
So by this point, we have a pretty good understanding of how this works.
That’s how we know Pangea existed, and that it was the latest
in a long line of supercontinents.
It’s also a big part of why we believe these landmasses form
and break up in cycles.
The cycles seem to last about five to seven hundred million years —
which means we’re about halfway through the current one.
But figuring out what the next supercontinent will be
is much easier said than done.
I mean, at first, it might seem really simple.
Like, just hit fast-forward on the Earth and assume the plates
will keep doing what they’re doing now.
Problem solved!
And that is an option geologists have looked at.
Overall, today’s big plate movements are still pretty similar
to the ones that first broke up Pangea:
Everything except Antarctica is drifting north, but the Americas
are also moving generally to the west, and Africa and Europe
are moving generally to the east.
This is all driven by activity happening at the boundary between their
tectonic plates, which sits smack in the middle of the Atlantic Ocean.
As the plates spread apart, the boundary gets wider and wider
by a few centimeters each year.
And as it opens, that creates a gap where rock from the mantle
comes to the surface to form new crust — in this case,
a huge mountain range called the Mid-Atlantic Ridge.
This whole process is called divergence,
and it spreads landmasses apart.
But... you can't keep pushing continents apart forever.
If new crust shows up in one place, it has to disappear somewhere else
— because like, Earth isn’t getting any bigger.
Right now, that disappearing act is mainly happening in the Pacific,
which is shrinking at about the same rate
that the Atlantic is growing.
It’s undergoing subduction, where the Pacific Plate
is being shoved under many of its neighbors.
So, overall, if you hit fast-forward and let today’s motions
keep going, you end up with the supercontinent Novopangea
in about 200 million years.
In this scenario, the Pacific will keep shrinking,
and the Atlantic will keep growing.
And eventually, Asia and the Americas will wrap themselves
around Australia somewhere around what used to be
the middle of the Pacific Ocean.
This scenario is called extroversion, where continents keep drifting
apart until they run into each other on the other side of the planet.
Novopangaea might seem like the obvious contender for our
next supercontinent, but a lot of geologists aren’t sold on it.
There are various reasons why, but the biggest one
is that plate motions and boundaries tend to change.
Just because something has been happening for 180 million years
doesn’t mean it has to go on forever.
And this is when predicting Earth’s future gets really messy.
For instance:
Today, the Atlantic might be expanding overall, but there are
three small subduction zones around its edges: one off
the southern coast of South America, one in the Caribbean,
and a really tiny one right around Gibraltar.
They’re small right now, but many geologists think they’ll grow as a
part of a Wilson cycle, where oceans tend to grow, pause, then shrink.
This happens when sources of heat and energy in the mantle shift
or disappear — things like big magma blobs.
And if this happens in the Atlantic, the tectonic plates
on either side of the Mid-Atlantic Ridge won’t have
any driving force pushing them outward.
So eventually, they’ll begin to sink under their own weight.
That means more crust will sink into those three small subduction zones.
And those zones will start to grow.
Now, it’s not clear if the Atlantic is part of a Wilson Cycle.
But if it is, it means the ocean will eventually stop growing and
start shrinking — pulling Eurasia, Africa, and the Americas together.
And that means no more Novopangea.
Instead, there are a couple other possibilities depending on
how exactly this plays out.
The first is Pangea Ultima.
With the Atlantic shrinking, there would be nothing significant
pushing together the tectonic plates around the Pacific.
So, in a hundred million years or so, the Pacific Ocean would start to grow.
Then, by about 250 million years from now, Africa would crash into the Americas.
And Pangea Ultima would be born.
This scenario, where continents come together around the same area
where they originally started spreading apart, is called introversion.
And like the name kind of suggests, it’s the opposite of extroversion,
where continents come together halfway around the world.
But again, things don’t have to be this way:
Wilson cycles in the Atlantic also lead to a second possibility.
So, most of Earth’s other big, divergent boundaries are around
the edges of the Indian Ocean.
And depending on things like how energy shifts in the mantle,
they could get bigger and even come to dominate the planet
once the Atlantic starts shrinking.
It’s still an “if”, but if it happens, the Pacific Plate
might keep subducting after all — even if the Atlantic does, too.
So, the Pacific will shrink to nothing... the Atlantic will shrink to nothing...
and we’ll be left with a supercontinent centered on the Americas, called Aurica.
Finally, though, there’s one last scenario — something that’s neither
introversion nor extroversion, but a little of both.
So, introversion says that new supercontinents form around
where the old one was, and extroversion says that they form
halfway around the world.
But according to one group of scientists,
neither of these is quite true, historically.
By looking at magnetic fields locked into rocks from different time periods,
this group was able to figure out where on the globe those rocks first formed.
And based on that, they found that Pangea formed about a quarter
of the way around the planet from the supercontinent before it, called Rodinia.
And Rodinia was about a quarter of the way around the planet
from the supercontinent before it.
They call this trend orthoversion.
And they think it happens because of the subduction that happens
around the edges of a supercontinent as it breaks up.
See, subducted plates don’t just disappear:
They dive deep into the mantle.
And when they do, some researchers think they melt and create
huge plumes of super-hot rock.
Then, those plumes rise up on the opposite side of the planet.
These scientists think it’s hard for continents to
move past these plumes, so they don’t.
Instead, as extroversion is breaking up a supercontinent,
any land that runs into these plumes just gets stuck there.
Then, eventually, introversion drags the rest of Earth’s land
to the same spot, creating a new supercontinent about
a quarter of the way around the world from the old one.
If you look at a map of where Pangea used to be, that would mean
the next supercontinent would form in the Arctic Ocean.
And according to this group, that’s what we’ll see in the future:
Almost all of Earth’s land will become concentrated at the North Pole
— except for Antarctica, which would stay around the South Pole
instead of joining the party up north.
This arrangement is called Amasia.
And besides being cool to think about, it’s also significant
in that it would really mess with Earth’s climate.
Mainly, having land at the poles instead of oceans makes it easier
for ice to form and stick around, which makes ice ages more extreme.
Like, when Rodinia was at the South Pole,
the entire planet was covered in ice.
So if Amasia happens in 150 million years, it might have some pretty
radical effects — not just on what Earth looks like,
but what it feels like, too.
But really, any supercontinent can change the climate pretty
dramatically, even if they don’t usher in a new ice age.
After all, when there’s just one landmass, you get radically
different ocean currents, which can have huge effects on how heat
and energy travel around the planet.
Plus, subducting ocean crust powers many volcanoes today.
And when you have a supercontinent and crust isn’t subducting,
you lose that.
You also lose the gases from volcanoes that help keep the climate stable
— so overall, a planet with a supercontinent can see
some pretty wild temperature swings.
Like, it’s no coincidence that when Pangea was around, Earth reached
some of its coldest and hottest points in the last 350 million years.
So, someday, Earth will look a lot different than the planet we know
— and it will feel a lot different, too.
Whether or not humans will be around then is a different story…
but hey: Even if we won’t be here to witness the next supercontinent,
understanding what it will be like can help us learn about
processes happening on Earth right now.
Like, to predict how continents move, we need to know how convection
in the mantle changes the crust and also how subducting crust
changes the mantle.
That means learning more about earthquakes and volcanoes.
And to know how all that affects climate, we need to know about
ocean currents and greenhouse gases and ice sheets and loads more.
So the next supercontinent may be a ways off,
but predicting what it will be means really learning more
about our planet, inside and out.
And that’s only ever a good thing.
Before you go, we wanted to let you know that the end of the month
is coming up — and that means our October Pin of the Month
is only available for a few more days.
Every month, we release a new space-related pin,
and this month’s is the Space Shuttle Atlantis.
It’s only available until November 1st, so if you want one,
you can head over to DFTBA.com/SciShow.
And as always, thanks for watching.
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