Almost 500 years ago, Flemish cartographer Gerardus Mercator produced one of the most important maps in the world.
It was certainly not the first attempt to create a world atlas, nor was it particularly accurate: Australia is absent, and the Americas are only sketchy.
Since then, cartographers have produced increasingly accurate versions of our continental arrangement, correcting Mercator’s errors as well as the biases between hemispheres and latitudes created by his projection.
But Mercator’s map, along with others produced by his 16th-century contemporaries, revealed a truly global picture of our planet’s landmasses — a perspective that has haunted people’s minds ever since.
What Mercator didn’t know is that continents weren’t always organized this way. He lived about 400 years before the plate tectonic theory was confirmed.
When looking at the position of the seven continents on a map, it is easy to assume that they are fixed. For centuries, humans have fought wars and sealed peace deals to conquer these territories, assuming that their land—and that of their neighbors—has always been and always will be there.
From Earth’s perspective, however, the continents are leaves adrift in a lake. And human worries are a drop of rain on the surface of the leaf.
The seven continents were once united into a single mass, a supercontinent called Pangea. And before that, there is evidence of others that go back more than three billion years: Panotia, Rodinia, Columbia/Nuna, Kenorland, and Ur.
Geologists know that supercontinents disperse and come together in cycles: we’re halfway through one now.
So what kind of supercontinent could there be in the future on Earth? How will the land masses we know today reorganize themselves in the long run?
There are at least four different possible trajectories ahead. And they show that Earth’s living beings will one day reside on a very different planet, which looks more like an alien world.
For geologist João Duarte, from the University of Lisbon in Portugal, the path to exploring Earth’s future supercontinents began with an unusual event in the past: an earthquake that shook Portugal on a Saturday morning in November 1755.
It was one of the most powerful earthquakes recorded in the last 250 years, with a total of 60,000 deaths and triggering a tsunami in the Atlantic Ocean. But what made him particularly strange was his location.
“There shouldn’t be big earthquakes in the Atlantic,” says Duarte. “It was weird.”
Earthquakes of this magnitude often happen in (or near) large subduction zones, where oceanic plates plunge beneath continents, melting and being consumed in the warm mantle. They involve collision and destruction.
The 1755 earthquake, however, happened along a “passive” edge, where the oceanic plate underlying the Atlantic smoothly transforms into the continents of Europe and Africa.
In 2016, Duarte and colleagues proposed a theory for what could be happening: the “seams” between these plates could be unraveling and a major rupture could be looming.
“It could be a kind of infectious mechanism”, he explains. Or like glass shattering between two tiny holes in a car windshield.
If so, a subduction zone could be about to spread from the Mediterranean across West Africa and perhaps even Ireland and the UK, generating volcanoes, mountain formation and earthquakes in those regions.
Duarte realized that, if that happens, it could lead, in the distant future, to the closure of the Atlantic. And if the Pacific continues to shrink as well — which is already happening along the “Ring of Fire” that surrounds it — a new supercontinent would eventually form.
He called it Aurica, because the ancient landmasses of Australia and the Americas would lie at its center.
It would be something like this:
After Duarte published his Aurica proposal, he wondered about other future scenarios. After all, his was not the only supercontinental trajectory geologists had proposed.
He then began talking to oceanographer Matthias Green of Bangor University in Wales. The two realized they needed someone with computer skills to create digital models.
“This person had to be someone a little special, who didn’t mind studying something that would never happen on human timescales,” he explains.
It turned out to be his colleague Hannah Davies, another geologist at the University of Lisbon.
“My work consisted of transforming drawings and illustrations by geologists of the past into something quantitative, georeferenced and in a digitized format,” says Davies.
The idea was to create models that other scientists could develop and improve.
But it wasn’t simple. “What made us nervous is that it’s an incredibly blue sky (where “real world” applications are not immediately apparent). It’s not the same as a regular scientific paper,” says Davies.
“We wanted to say, ‘Okay, we understand a lot about plate tectonics after 40 or 50 years (of scientific research). And we understand a lot about the dynamics of the mantle and all the other components of the system. How far can we take that knowledge into the future? ?'”
This led to four scenarios. In addition to outlining a more detailed picture of Aurica, they explored three other possibilities, each projecting into the future about 200 to 250 million years from now.
The first was what might happen if the status quo continue: the Atlantic remains open, and the Pacific closes. In this scenario, the supercontinent that will form will be called Novopangeia.
“It’s the simplest and most plausible based on what we understand now,” says Davies.
However, there could also be geological events in the future that lead to different arrangements.
One example is a process called “orthoversion”, in which the Arctic Ocean closes, and the Atlantic and Pacific remain open.
This changes the dominant orientations of tectonic expansion, and the continents move northward, all arranged around the North Pole except Antarctica.
In this scenario, a supercontinent called Amasia forms:
Finally, it is also possible that seafloor expansion in the Atlantic Ocean could slow down. In the middle of the ocean, there is a giant ridge that divides two plates, crossing Iceland to the Southern Ocean. Here, a new lithosphere is forming, like a conveyor belt.
If this expansion slows down or stops, and if a new edge of subduction plates forms along the east coast of the Americas, we will have a supercontinent called Pangea Ultima, which looks like a huge atoll:
These four digital models now mean that geologists have a basis for testing other theories.
For example, scenarios can help scientists understand the effects of different supercontinental arrangements on tides as well as weather in the distant future — what would the weather be like in a world with a huge ocean and a giant land mass?
To simulate the climate of a supercontinent, “you can’t use IPCC models [Painel Intergovernamental sobre Mudanças Climáticas]because they weren’t made for that”, says Duarte.
“You can’t change the variables you need to change (for a simulation like that).”
Simulations of Earth’s future supercontinents can also serve as an indicator for understanding the climate of exoplanets.
“Future Earth is completely alien,” says Davies. “If you were orbiting Aurica, or Novopangea, you probably wouldn’t recognize it as Earth, but another planet with similar colors.”
That idea led the trio to collaborate with Michael Way, a physicist at the Goddard Institute for Space Studies at NASA, the American space agency. He and his colleagues are dedicated to studying climates on alien worlds by simulating the variations of ours over time.
“We don’t have that many examples of what a temperate climate might look like. Well, we have one example to be honest: Earth, but we have Earth over time,” says Way.
“We have the scenarios from the past, but moving forward to the future and using these wonderful tectonic models for the future gives us another combination to add to our collection.”
You need these models because it can be difficult to know what to look for when looking at potentially habitable exoplanets from afar.
Ideally, you want to know if a planet has a supercontinent cycle, because the presence of life and active tectonic plates can be intertwined. The continental arrangement could also affect the likelihood of having liquid water.
Through the lens of telescopes, the continents cannot be seen, and the atmospheric composition can only be inferred. Thus, models of climatic variations could reveal some indirect signal that astronomers could detect.
Way’s simulation of the climates of the supercontinents — which took months using a supercomputer — revealed some striking variations between the four scenarios.
Amasia, for example, would lead to a planet much colder than the rest. With land concentrated around the North Pole, and oceans less likely to carry warm currents to cooler latitudes, ice sheets would accumulate.
The climate in Aurica, on the other hand, would be milder, with a dry interior, but coastlines similar to those of Brazil today, with more water in a liquid state.
It’s useful to know all this because if an Earth-like exoplanet has plate tectonics, we won’t know what stage of the supercontinent’s cycle it is currently in, so we’ll need to know what to look for to infer its habitability.
We must not assume that the land masses will disperse, in the middle of the cycle, like ours.
As for the future of our own planet, Davies acknowledges that the four supercontinent scenarios they simulated are speculative, and there could be unforeseen geological surprises that change the outcome.
“If I had a time machine to look at, I wouldn’t be surprised if, in 250 million years, the supercontinent doesn’t look anything like any of these scenarios. There are a lot of factors involved,” she says.
However, what can be said with certainty is that the land masses we take for granted today will one day reorganize into an entirely new configuration.
Countries that were once isolated from each other will be close neighbors. And if Earth still harbors intelligent beings, they could travel between the ancient ruins of New York, Beijing, Sydney and London without ever seeing an ocean.
Read the entirety of this report (in English) on the BBC Future website.
