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The outer layer of the Earth, the solid crust on which we walk, is composed of broken pieces, much like the shell of a broken egg. These pieces, the tectonic plates, move around the planet at a speed of a few centimeters per year. From time to time, they come together and combine to form a supercontinent that remains a few hundred million years before they separate. The plates disperse or scatter and move away from each other until they regain their shape after 400 to 600 million years.
The last supercontinent, Pangea, was formed about 310 million years ago and began to separate about 180 million years ago. It has been suggested that the next supercontinent will form in 200 to 250 million years. So we are about halfway through the dispersed phase of the current supercontinent cycle. The question is how will the next supercontinent be formed and why?
There are four basic scenarios for the formation of the next supercontinent: Novopangea, Pangea Ultima, Aurica and Amasia. The way in which each is formed depends on different scenarios, but ultimately depends on the separation of Pangea and how continents are still moving today.
The dissolution of Pangea led to the formation of the Atlantic Ocean, which is opening and expanding today. As a result, the Pacific Ocean is closing and shrinking. The Pacific is home to a ring of subduction zones around its periphery (the "fire circle"), where the ocean floor is lowered or subducted beneath continental plates and inside the Earth. There, the old ocean floor is recycled and can sink into volcanic plumes. The Atlantic, on the other hand, has a large oceanic ridge producing a new oceanic plate, but contains only two subduction zones: the Lesser Antilles arc in the Caribbean and the Scotia Arc between South America and Antarctica.
1. Novopangea
If we assume that the current conditions persist, so that the Atlantic continues to open and the Pacific continues to close, we have a scenario where the next supercontinent is formed at the antipodes of Pangea. The Americas would collide with Antarctica drifting north, and then into Africa-Eurasia already colliding. The supercontinent that would then be called Novopangea or Novopangaea.
2. Pangea Ultima
The opening of the Atlantic could, however, slow down and even begin to close. The two small subduction arches of the Atlantic could extend to the eastern shores of the Americas, leading to a reform of Pangea at a time when the Americas, Europe and Africa would be united in a supercontinent called Pangea Ultima. This new supercontinent would be surrounded by a great Pacific Ocean.
3. Aurica
However, if the Atlantic were to create new subduction zones – which may already be the case – the Pacific and Atlantic oceans could be condemned to close. This means that a new ocean basin should be formed to replace them.
In this scenario, the pan-Asian divide that crosses Asia from western India to the Arctic opens to form the new ocean. The result is the formation of the supercontinent Aurica. Because of Australia's current drift to the north, Australia would be at the center of the new continent, as East Asia and the Americas close the Pacific on both sides. The European and African plates would then join the Americas at the closing of the Atlantic.
4. Amasia
The fourth scenario predicts a completely different fate for the future Earth. Many of the tectonic plates are currently moving northward, particularly in Africa and Australia. This drift is thought to be due to anomalies left by the Pangea, deep in the interior of the Earth, in the part called the mantle. Because of this northern drift, one can envision a scenario in which continents, except Antarctica, will continue to drift north. This means that they would eventually gather around the North Pole in a supercontinent called Amasia. In this scenario, the Atlantic and the Pacific would remain primarily open.
We believe that Novopangea is the most likely of these four scenarios. This is a logical progression of the current direction of continental plate drift, while the other three assume that another process is taking place. New Atlantic subduction zones should be created for Aurica, the inversion of the Atlantic opening for Pangea Ultima or anomalies in the interior of the Earth left by Pangea for Amasia.
The investigation of the Earth's tectonic future requires us to push the boundaries of our knowledge and reflect on the processes that shape our planet in the long term. This also brings us to think about the Earth system as a whole and raises a series of other questions: what will be the climate of the next supercontinent? How is ocean circulation going to adjust? How will life evolve and adapt? These are the kinds of questions that push the boundaries of science because they push the limits of our imagination.
Mattias Green is a physical oceanography reader from the University of Bangor, UK; Hannah Sophia Davies is a PhD student at the Universidade de Lisboa and Joao C. Duarte is a researcher and coordinator of the Marine Geology and Geophysics Group of the Universidade de Lisboa, Portugal.
This article is republished from The Conversation under a Creative Commons license. Read the original article.
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