Plate tectonics of the far future

As we should all know, the earth’s plates are on the move. The theory of plate tectonics is a well-supported mechanism for the movement of the continents in deep time. It explains many prior observations about geology and biogeography, and can be directly observed today via GPS. It makes sense that therefore plate tectonics will continue forward into the future. But what exactly will happen?

In short, we don’t know for sure. But it’s a fun topic to speculate on, so I’m gonna talk about it.

Earth 50 million years in the future, from Dougal Dixon’s pioneering speculative evolution work After Man (Dixon 1981). As far as I know, this is the earliest example of future cartography.

The first thing to do is to look at what directions the continents are going in now. In recent geological history, the Americas have been moving west as the mid-Atlantic ridge continues to create new oceanic crust. The former pieces of Gondwana have been moving northward as well, pulled by subduction zones to the north. These trends will probably continue into the future. We can safely infer that in the relatively recent geological future, the Atlantic will continue to widen as the Americas move west; in turn, the Pacific will shrink as it subducts under eastern Asia and Oceania. Africa and Australia are both moving northward, and if this trend continues they will eventually collide with Eurasia, forming large mountain ranges where Indonesia and the Mediterranean are now (Scotese 2003). The East African rift valley will widen and eventually become a new sea as the Somalian Plate moves eastward, splitting Africa into two continents (Pérez Díaz 2018); the new continent of East Africa will follow a similar trajectory to Madagascar and India, eventually colliding with them to form what van Hinsbergen and Schouten (2021) deem the Somalayan orogeny. California will be dragged north as the Pacific Plate moves northweest, bringing it closer to Alaska (Scotese 2003). And it’s also possible that subduction zones in southern Asia or near South America may drag Antarctica north from its polar position (Manaugh and Twilley 2013). This would inevitably lead to the melting of the Antarctic ice caps as the continent moves into temperate or even tropical latitudes.

The Somalian Plate 50 million years in the future, from van Hinsbergen and Schouten 2021

That’s pretty solid for the first 50 million years or so. But what will happen after that? After approximately that point, there’s so much potential for unpredictable tectonic shifts that almost nothing can be predicted with absolute certainty (Manaugh and Twilley 2013). Almost.

There is one pretty solid idea that we can drag into the future, though: the “supercontinent cycle”. Approximately every 500 million years, the continents will go through a cycle of coming together, moving apart, and coming together again. This has been happening for at least the past two billion years (Nance et al. 2014). The last supercontinent, Pangaea, assembled in the late Carboniferous/early Permian and broke apart at the beginning of the Jurassic (Blakey 2003). Right now, we are roughly in the middle of a supercontinent cycle, with the continents broken apart.

It should be noted that the supercontinent cycle is not the same as a Wilson cycle. Wilson cycles are cycles of individual oceanic opening and closing along certain sutures, which don’t necessarily line up with supercontinent formation.

A supercontinent is surrounded by a “super-ocean”; the most recent one of these was Panthalassa, which surrounded Pangaea. When supercontinents break up, oceans must form between the now-split continents. The Atlantic Ocean is a very good example of this, being formed through Pangaea’s breakup. There are two main models for what happens afterwards: introversion and extroversion. Introversion basically means that the more recently formed ocean’s crust will eventually start subducting and the ocean will close again, while extroversion means that the more recent ocean continues to widen and the older ocean closes instead (Davies et al. 2018). Under introversion, the Atlantic would eventually close, and under extroversion, it would keep widening. In practice, though, there can be more than two oceans, so scenarios can get much more complex than just that. A third model, orthoversion, has been proposed, where a third ocean closes to form the supercontinent instead (Mitchell et al. 2012). Recent simulations involving past supercontinent cycles suggest that supercontinent cycles may be modulated by a combination of introversion and extroversion (Yoshida and Santosh 2014), or alternating phases of introversion and extroversion (Li et al. 2019). So that’s also a possibility for the future.

Extrapolating the supercontinent cycle into the future, the next supercontinent will form in roughly 200-300 million years (and then break apart again in ~500 million years). There are four major hypotheses for this future supercontinent outlined by Davies et al. (2018): Pangaea Ultima, Novopangaea, Amasia, and Aurica. This isn’t the only suite of possibilities, but if we listed every possible configuration we’d be here forever. Each of these follows a different model of the supercontinent cycle:

The four proposed supercontinent arrangements. Courtesy Hannah S. Davies.

Pangaea Ultima, also known as Pangaea Proxima, is most commonly associated with Christopher Scotese, although the model had also been suggested by other authors (e.g. Hoffmann 1999). It follows the introversion model: the mid-Atlantic ridge will stop widening, and as subduction zones form, the Pacific will widen again and the Atlantic will shrink. This brings the Americas back together with Africa and Eurasia. The resulting supercontinent would not be far geographically from Pangaea (hence the name). This model lines up most nicely with the classical concept of a Wilson cycle, which in this case would apply to the Atlantic.

Pangaea Ultima as modeled by Christopher Scotese. I think Scotese’s work is the first serious attempt to model future plate tectonics based on past trends

Novopangaea was first proposed by Roy Livermore in the 1990s (Nield 2007). It follows the extroversion model: as the Atlantic widens, the Pacific Plate will subduct. This narrows the Pacific Ocean, bringing the Americas into collision with eastern Asia and Australia. The supercontinent will be centered at the opposite side of the globe as Pangaea. This is the model followed by The Future is Wild, which calls it Pangaea II (Dixon and Adams 2003).

Amasia was first coined by Hoffmann (1999) for an extroversion model. However, a model for the formation of Amasia that differentiates it from Pangaea Ultima and Novopangaea (and the one we focus on here) was proposed by Mitchell et al. (2012). It follows the orthoversion model: the Arctic Ocean closes, bringing the continents together over the north pole, while the Pacific and Atlantic Oceans merge into a superocean. Antarctica stays where it is. The center of Amasia would be displaced from the center of Pangaea by ~90 degrees. This lines up with Mitchell et al. (2012)’s estimates for the arc of divergence between the centers of Pangaea and the earlier supercontinent Rodinia, and between Rodinia and the even earlier Nuna; if that continues into the future, the next supercontinent will have a similarly displaced center.

How Amasia forms. Adapted from Mitchell et al. 2012

Aurica was first proposed by Duarte et al. (2018). It proposes a combination of introversion and extroversion, which may have been the case for past supercontinents (e.g. Yoshida and Santosh 2014). Both the Pacific and Atlantic Oceans close (both already have quite old oceanic crust). At the same time, a new ocean opens up in the middle of Eurasia. This eventually forms the basis of the new superocean, and the supercontinent has the Americas sandwiched between two halves of Eurasia, with Africa on one side and Australia on the other.

Which of these is most likely? We don’t know. If one model of supercontinent formation was prevalent in the past, it would make sense if that went forward into the future. But nature is more complicated than that; past supercontinents were variously formed by introversion, extroversion, or a combination of one of those and orthoversion (Davies et al. 2018). So there’s no way to tell which of these may happen. An Aurica-type scenario, with elements of introversion, extroversion, and/or orthoversion, could perhaps be the safest bet based on our understanding of previous supercontinent formation, but the nuances are impossible to predict. Any possibility is on the table.

We can use what we know about previous supercontinents to guide our predictions for what the next supercontinent would be like climatically and biotically. The interior of the supercontinent would be very arid, being far away from rain clouds forming over the superocean (Williams and Nield 2007). Based on what has been modeled for Pangea, a large portion of the supercontinent’s interiormost regions may be almost uninhabitable, with highs potentially reaching over 45°C/113°F – as hot as Death Valley in the summer (Crowley et al. 1989). All the rain would be dumped on coastal regions in torrents, probably via catastrophic seasonal monsoons. These “megamonsoons” are thought to have battered the coasts of Pangaea (Kutzbach and Gallimore 1989). The rain would fuel the growth of rainforests along the coasts, while preventing moisture from heading further inland. So while the coasts would be highly seasonal, the rest of the continent would be year-round desert. The open oceans would be stagnant, being too far from continents for currents to run; marine life would thrive closer to the coast, though (Williams and Nield 2007). Depending on if much of the land is near one of the poles, massive ice caps could form there, fueling the start of another ice age (Way et al. 2021), as happened when Pangaea formed.

To cap off this post, I’m gonna bring up perhaps the only appearance of a future supercontinent in media outside of The Future is Wild and other speculative evolution projects. Nintendo’s Pikmin series take place on a planet known to the players’ species as PNF-404. It is very obviously meant to be Earth, and the devs have all but said that it takes place on an Earth where humans have gone extinct (as evidenced by the amount of artifacts left behind). The first two games merely represent the planet with modern day Earth, but Pikmin 3 does something different. While PNF-404 is now no longer identical to modern-day Earth, they do look suspiciously like rearranged Earth continents…

PNF-404 in Pikmin 3

When you dig into the game’s files to get the texture for that globe, you find a continental arrangement that looks a lot like Scotese’s model of Pangaea Ultima, down to the enclosed sea in the middle. It’s even referred to in the files as “pangaeaUltima”!

I just thought that was pretty cool.

References
Blakey, R.C. (2003). “Carboniferous-Permian paleogeography of the assembly of Pangaea”. In: Wong, T.E. (ed.). Proceedings of the XVth International Congress on Carboniferous and Permian Stratigraphy, Utrecht.
Davies, H.S.; Mattias Green, J.A.; Duarte, J.C. (2018). “Back to the future: Testing different scenarios for the next supercontinent gathering”. Global and Planetary Change 169: 133-44.
Dixon, D. (1981). After Man. St Martin’s Press.
Dixon, D.; Adams, J. (2003). The Future is Wild. Firefly Press.
Hoffman, P.F. (1999). “The break-up of Rodinia, birth of Gondwana, true polar wander and the snowball Earth”. Journal of African Earth Sciences 28(1): 17-33.
Kutzbach, J.E.; Gallimore, R.G. (1989). “Pangaean climates: Megamonsoons of the megacontinent”. Journal of Geophysical Research: Atmospheres 94(D3): 3341-57.
Li, Z.X.; Mitchell, R.N.; Spencer, C.J.; Ernst, R.; Pisarevsky, S.; Kirscher, U.; Murphy, J.B. (2019). “Decoding Earth’s rhythms: Modulation of supercontinent cycles by longer superocean episodes”. Precambrian Research 323: 1-5.
Manaugh, G.; Twilley, N. (2013). “What Did the Continents Look Like Millions of Years Ago?”. The Atlantic.
Mitchell, R.N.; Kilian, T.M.; Evans, D.A.D. (2012). “Supercontiennt ycles and the calculation of absolute palaeolongitude in deep time”. Nature 482: 208-11.
Nance, R.D.; Murphy, J.B.; Santosh, M. (2014). “The supercontinent cycle: A retrospective essay”. Gondwana Research 25: 4-29.
Nield, T. (2007). Supercontinent: Ten Billion Years in the Life of Our Planet. Harvard University Press.
Nordt, L.; Atchley, S.; Dworkin, S. (2015). “Collapse of the Late Triassic megamonsoon in western equatorial Pangea, present-day American Southwest”. GSA Bulletin 127(11-12): 1798-815.
Pérez Díaz, L. (2018). “Africa is splitting in two – here is why“. The Conversation.
Scotese, C. (2003). “PALEOMAP Project”. http://scotese.com/.
van Hinsbergen, D.J.J.; Schouten, T.L.A. (2021). “Deciphering paleogeography from orogenic architecture: Constructing orogens in a future supercontinent as thought experiment”. American Journal of Science 321(6): 955-1031.
Way, M.J.; Davies, H.S.; Duarte, J.C.; Green, J.A.M. (2021). “The Climates of Earth’s Next Supercontinent: Effects of Tectonics, Rotation Rate, and Insolation”. Geochemistry, Geophysics, Geosystems 22(8): e2021GC009983.
Yoshida, M.; Santosh, M. (2014). “Mantle convection modeling of the supercontinent cycle: Introversion, extroversion, or a combination?”. Geoscience Frontiers 5(1): 77-81.

One thought on “Plate tectonics of the far future

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s