Geology: how will the next 'super continent' form?

 

It was certainly not the first attempt at a world atlas, and it was not particularly accurate either: Australia is absent, and the Americas are only roughly drawn. Since then, cartographers have produced ever more accurate versions of this continental layout, correcting Mercator's errors and 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 the Earth's landmass

Mercator 1569 world map

Crédit photo, Wikimedia Commons

What Mercator did not know was that the continents were not always arranged in this way. He lived about 400 years before the theory of plate tectonics was confirmed.

When you look at the position of the seven continents on a map, it is easy to assume that it is fixed. For centuries, human beings have fought wars and made peace for their share of these territories, assuming that their land - and that of their neighbours - has always been there, and always will be.

From the Earth's point of view, however, the continents are leaves drifting on a pond. And human concerns are a drop of water on the surface of the leaf. The seven continents were once joined together in a single mass, a supercontinent called Pangea. And before that, there is evidence that other continents existed for over three billion years: Pannotia, Rodinia, Columbia/Nuna, Kenorland and Ur.

Geologists know that super continents break up and come together in cycles: we are currently halfway through one. So what kind of super continent might be in the Earth's future? How will the landmasses as we know them reorganize in the very long term? It turns out that there are at least four different trajectories that could emerge. And they show that Earth's living beings will one day reside on a very different planet, one that looks more like an alien world.

For geologist Joao Durarte It was one of the most powerful earthquakes of the last 250 years, killing 60 000 people and causing a tsunami in the Atlantic Ocean. What made it particularly strange was its location. "You shouldn't have big earthquakes in the Atlantic," Duarte says. "It was strange."

Earthquakes of this magnitude typically occur at or near major subduction zones, where oceanic plates dip beneath continents and are melted and consumed in the hot mantle. They involve collisions and destruction. The 1755 earthquake, however, occurred along a 'passive' boundary, where the oceanic plate underlying the Atlantic makes a smooth transition to the European and African continents.

In 2016, Duarte and colleagues proposed a theory about what might be happening: the sutures between these plates could be unravelling, and a major rupture could be imminent. "It could be some kind of infectious mechanism," he explains. Or like the glass that shatters between two small holes in a car windscreen. If so, a subduction zone could be poised to spread from the Mediterranean to West Africa and possibly as far as Ireland and the UK, causing volcanoes, mountain building and earthquakes in those regions.

Duarte a réalisé que, si cela se produit, l'Atlantique pourrait finir par se fermer. Et si le Pacifique continuait à se fermer également - ce qui se produit déjà le long du "cercle de feu" de subduction qui l'entoure - un nouveau supercontinent finirait par se former. Il l'a appelé Aurica, ainsi nommé parce que les anciennes masses continentales de l'Australie et des Amériques se trouveraient en son centre.

After publishing his proposal for Aurica, Duarte wondered about other future scenarios. After all, the trajectory of his supercontinent was not the only one that geologists had proposed.

So he started talking to oceanographer Matthias Green from Bangor University in Wales. The two men realised they needed someone with the computer skills to create numerical models. "It had to be someone who was a bit special, who wasn't afraid to study something that would never happen on a human scale," he explains. That person turned out to be his colleague Hannah Davies, another geologist at the University of Lisbon. "My job was to transform the drawings and illustrations of past geologists into quantitative, georeferenced and digitised data," explains Hannah Davies. The idea was to create models that other scientists could use and refine.

But it wasn't easy. "What made us nervous was that this is an incredibly abstract subject. It's not the same as an ordinary scientific paper," says Davies. We wanted to say, 'OK, we understand plate tectonics after 40 or 50 years. And we know just as much about the dynamics of the mantle and all the other components of the system. How far can we go with this knowledge in the future?  

Four scenarios were developed. In addition to modelling a more detailed picture of Aurica, they explored three other possibilities, each looking forward about 200 to 250 million years.

The first was what might happen if the status quo continues: the Atlantic remains open and the Pacific closes. In this scenario, the supercontinent that forms will be called Novopangaea. "It's the simplest, and the most plausible based on what we understand at the moment," says Davies.

However, geological events could also occur 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 spreading, and the continents drift northwards, all arranging themselves around the North Pole, with the exception of Antarctica.