Pangea: we may have a new supercontinent in the future – 11/30/2023 – Fundamental Science

In 1912, German meteorologist Alfred Wegener presented his hypothesis of continental drift to the world. One of the pillars of this theory was the observation, already confirmed by other scientists, that the coastlines of the different continents appear to come together, like a puzzle, if we mentally subtract the oceans that separate them. The east coast of Brazil, for example, fits almost perfectly into the west coast of Africa. Wegener gathered diverse evidence that indicated that the types of rocks, geological structures and fossils found on both sides of the Atlantic in fact suggest that one day the two continental masses, which are today South America and Africa, formed a single block: Pangea.

Wegener’s theory was rejected by most scientists. One of the problems they highlighted concerned the mechanism capable of making large continents move freely on the Earth’s surface, to the point that one day they were together and, millions of years later, separated. After almost half a century of scientific discoveries, it was understood that the continents are based on tectonic plates, the rocky blocks that make up the Earth’s lithosphere. And that, in fact, continents meet and separate more than we can imagine.

Tectonic plates are large fragments of lithosphere (a layer made up of the crust and part of the mantle, which behaves rigidly) that float on an asthenosphere (a layer made up of the rest of the mantle, which, due to its composition and the temperatures and pressures inside the globe, it moves more fluidly on geological time scales).

Below the asthenosphere, in the interior of the planet, we have the Earth’s core, which is even hotter. The asthenosphere works like a kettle of boiling water: the lower part of the molten mantle in contact with the hottest core is constantly heated, which causes its density to be lower than that of the upper layers of the mantle. The columns of hot mantle rise slowly, while in the upper layers the colder mantle tends to sink back to the bottom of the Earth, where it will be reheated by contact with the core, thus continuing the cycle in large convection currents.

When these currents reach the top of the convection column, they help to drag the rigid tectonic plates that are at the surface, in immediate contact with the asthenosphere, until they become cold and dense enough to sink into the mantle, in the so-called zones of convection. subduction. This movement is one of the main drivers of plate tectonics that drives the drift of continents, that is, the gradual change of position on the Earth’s surface.

This dance of the continents allows them, from time to time, to meet and separate, forming new continental masses and different paleogeographic configurations. Today we know, for example, that between around 335 million and 200 million years ago almost all continental masses were together in a single block (called paleocontinent), Pangea, which separated thanks to the opening of the Atlantic Ocean, which occurred from about 200 million years ago.

When a paleocontinent contains more than 75% of all Earth’s continental masses, we say it is a supercontinent. And Pangea was not the first: this global meeting of continental masses occurred several times in the past, creating the supercontinents Rodinia, around 1 billion years ago, and Columbia, around 1.8 billion years ago, as well as possible others. old ones. And as for the future, will the continental fragments find themselves in new positions, redesigning the land masses?

Everything indicates yes, but the exact places where they could collide and form a new block is the subject of intense debate. Some scientists believe that the current movement of the continents will continue, and thus the Atlantic Ocean will become larger and the Pacific smaller, due to the dip of its oceanic plates in the areas that form the so-called Ring of Fire, where most of the volcanoes are concentrated. .

This configuration would lead to the future collision of the west coast of the Americas with the east coast of Asia, a model proposed by South African geologist Chris Hartnady in 1992. At the end of the 90s, the Englishman Roy Livermore presented a similar model, which he called Novopangeia , with a slightly different fit of the coastlines and the involvement of Antarctica, which does not appear in the previous one.

There are, however, alternatives. If the movement of the continents is reversed due to changes in convection patterns in the asthenosphere, the Atlantic Ocean could once again be consumed, while the Pacific Ocean will expand. Such a future would lead the Americas to once again collide with the east coast of Africa and Europe, generating the supercontinent that the American Christopher Scotese named Pangea Ultima, but later changed to Pangea Proxima, to avoid the name referring to an end of the world. cycle of continents.

The two processes, of closing the Pacific and the Atlantic, respectively, can be understood in different terms of continental cycles. In the first case, the continents that separated when Pangea ruptured would end up colliding with other fragments on the other side of the world, that is, the edges that collide are different from those continental edges that separated and today seem to fit together like breaking pieces. -head. This process is called extroversion.

In the second possibility, the continental edges that moved away would be more or less the same ones that will collide again in the future, a process called introversion, in which the movement of the continents would resemble that of an accordion, opening and closing according to the development of the oceans between they.

But there is still a third possibility. An idea led by the American Ross Mitchell, now at the Chinese Academy of Sciences, is that new supercontinents will form approximately 90 degrees from their predecessors — hence the so-called orthoversion, from “orthogonal” — due to the aggregation of continental fragments in places where the cold mantle is descending to the core. In this vision, it would be the Arctic Ocean that would close, causing the collision of the current continents at the North Pole to form Amasia (Americas + Asia), following a previous proposal by Canadian geologist Paul Hoffman.

In addition to introversion, extroversion and orthoversion, in 2018 another mechanism was proposed by the Portuguese João Duarte and his collaborators. From observing earthquakes on the margins of the Iberian peninsula, they came to the conclusion that it is possible that subduction zones — those in which oceanic plates colliding with other oceanic plates or with continental plates diving beneath the latter — begin to develop in the edges of the Atlantic, while continuing to operate in the Pacific, in order to generate two circles of fire, each of them bordering one of the oceans.

Such a scenario could lead, in the future, to the simultaneous consumption of the planet’s two largest oceans, a situation only possible if a new ocean were generated somewhere, perhaps tearing Eurasia in half. Duarte and collaborators called the new supercontinent that would result from this process Aurica (as Australia and the Americas would end up at the center of the new configuration).

In any case, if plate tectonics follows its current processes, the phenomenon will only occur in around 200 million years. Until then, no humans will likely be around to see what life will be like on Novopangeia, Pangea Proxima, Amasia or Aurica.

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Fabrício Caxito is a professor of geology, main researcher in the GeoLife MOBILE project and philosopher at UFMG.

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