The continents are moving. When will they collide? - Jean-Baptiste P. Koehl
In the early 20th century,
a meteorologist named Alfred Wegener
noticed striking similarities
between the coasts
of Africa and South America.
These observations led him to propose
a controversial new theory:
perhaps these and many other continents
had once been connected
in a single, gigantic landmass.
Wegener’s Theory of Continental Drift
directly contradicted the popular opinion
that Earth’s continents had
remained steady for millennia,
and it took almost 50 years
for his advocates
to convince the larger
scientific community.
But today, we know something
even more exciting—
Pangea was only the latest
in a long lineage of supercontinents,
and it won’t be the last.
Continental Drift laid the foundation
for our modern theory of plate tectonics,
which states that Earth’s crust
is made of vast, jagged plates
that shift over a layer of partially
molten rock called the mantle.
These plates only move at rates
of around 2.5 to 10 centimeters per year,
but those incremental movements
shape the planet's surface.
So to determine when a new
supercontinent will emerge,
we need to predict where these plates
are headed.
One approach here is to look
at how they’ve moved in the past.
Geologists can trace the position
of continents over time
by measuring changes
in Earth’s magnetic field.
When molten rock cools,
its magnetic minerals are “frozen”
at a specific point in time.
So by calculating the
direction and intensity
of a given rock’s magnetic field,
we can discover the latitude at which
it was located at the time of cooling.
But this approach has serious limitations.
For one thing, a rock’s magnetic field
doesn’t tell us the plate’s longitude,
and the latitude measurement
could be either north or south.
Worse still, this magnetic data gets
erased when the rock is reheated,
like during continental collisions
or volcanic activity.
So geologists need to employ other methods
to reconstruct the continents’ positions.
Dating local fossils and comparing them
to the global fossil record
can help identifying
previously connected regions.
The same is true of cracks and other
deformations in the Earth's crust,
which can sometimes be
traced across plates.
Using these tools,
scientists have pieced together
a relatively reliable history
of plate movements,
and their research revealed a pattern
spanning hundreds of millions of years.
What’s now known as the Wilson Cycle
predicts how continents
diverge and reassemble.
And it currently predicts
the next supercontinent will form
50 to 250 million years from now.
We don’t have much certainty
on what that landmass will look like.
It could be a new Pangea that emerges
from the closing of the Atlantic.
Or it might result from the formation
of a new Pan-Asian ocean.
But while its shape and size
remain a mystery,
we do know these changes will impact
much more than our national borders.
In the past, colliding plates have caused
major environmental upheavals.
When the Rodinia supercontinent
broke up circa 750 million years ago,
it left large landmasses
vulnerable to weathering.
This newly exposed rock absorbed
more carbon dioxide from rainfall,
eventually removing so much
atmospheric CO2
that the planet was plunged
into a period called Snowball Earth.
Over time, volcanic activity released
enough CO2 to melt this ice,
but that process took another
4 to 6 million years.
Meanwhile, when the next
supercontinent assembles,
it's more likely to heat things up.
Shifting plates and continental collisions
could create and enlarge
cracks in the Earth’s crust,
potentially releasing huge amounts
of carbon and methane into the atmosphere.
This influx of greenhouse gases
would rapidly heat the planet,
possibly triggering a mass extinction.
The sheer scale of these cracks would
make them almost impossible to plug,
and even if we could, the resulting
pressure would just create new ruptures.
Fortunately, we have at least 50 million
years to come up with a solution here,
and we might already be onto something.
In Iceland, recently conducted trials
were able to store carbon in basalt,
rapidly transforming these
gases into stone.
So it’s possible a global network of pipes
could redirect vented gases
into basalt outcrops,
mitigating some of our emissions now and
protecting our supercontinental future.
