Four plausible scenarios for the supercontinent of the future.
- We're halfway through a 'supercontinent cycle'.
- The next one is due in 200-300 million years.
- Here are four plausible scenarios of what it will look like.
Moving at fingernail speed
How the American, African and European continents once fit together before the Atlantic – and may one day again, if and when the local 'Wilson cycle' reverses.
Credit: Jacques Kornprobst, after E. Bullard et al. (1965), CC BY-SA 4.0
For things so massive and seemingly immovable, continents are pretty hard to pin down. Of course, that's because they do move, if only at the speed at which your fingernails grow: about two inches (5 cm) per year.
Accelerate the film of Earth's geology, and you see the landmasses dance across the globe like islands of foam on a running bath. One peculiarity of our drifting continents is that they tend to combine, over massive amounts of time, into one single supercontinent. It helps that the Earth is round, unlike your bath.
Then, millions of years later, tectonic forces cause the supercontinent to break up again – only for the individual continents to recombine much, much later. All at fingernail speed.
The usual suspects
Norwegian map of what the supercontinent of Columbia/Nuna may well have looked like, 1,590 million years ago.
Credit: Bjoertvedt, CC BY-SA 3.0
Here's one question with an un-pin-downable answer: How many supercontinents have there been in Earth's deep past? At least three or at least seven; as many as 11 or perhaps even a few more. Like the continents themselves, scientific theories diverge. Here are some of the usual suspects (most recent first, ages are approximate):
- Pangea (300-180 million years ago)
- Gondwana (600-180 mya)
- Pannotia (630-540 mya)
- Rodinia (1.1 bya-750 mya)
- Columbia, a.k.a. Nuna (1.8-1.5 billion years ago)
- Kenorland (2.7-2.1 bya)
- Ur (2.8-2.4 mya)
- Vaalbara (3.6-2.8 bya)
That's if we spool back the tape. What happens if we fast-forward? Even though Pangea, the last supercontinent, broke up almost 200 million years ago, geologists are pretty sure there will be another one, but not for some time to come. Right now, we're about halfway through a 'supercontinent cycle'. The next one will be around between 200 and 300 million years from now.
Wilson cycles
John Tuzo Wilson (1908-93) refined and championed the theory of plate tectonics in the 1960s, when it was still controversial. He was the first non-U.S. citizen to become president of the American Geophysical Union.
Credit: UC Davis
That brings us to the next question with an answer that's hard to pin down: What will that next supercontinent look like? That is, of course, unknowable, as no one alive today will be around to check. But one can speculate. Using what we know about the tectonic forces that power the movements of continental plates, three scientists line up four plausible scenarios for the formation of the next supercontinent.
In "Back to the future: Testing different scenarios for the next supercontinent gathering," Hannah S. Davies, J.A. Mattias Green, and Joāo C. Duarte present four supercontinents, each the outcome of a different tectonic what-if.
Each scenario is a different combination of two basic drivers of continental conglomeration (and fragmentation): the supercontinent cycle itself, and the so-called Wilson cycle.
In 1966, Canadian geologist John Tuzo Wilson proposed that the Atlantic had opened up along a zone where another ocean had previously existed. A 'Wilson cycle' therefore describes the cyclical opening and closing of ocean basins. Since those aren't necessarily in sync with supercontinent cycles, they can lead to various outcomes – supercontinents of different shapes and at different types.
The next supercontinent will take shape when at least one ocean closes. That can happen in one of two ways:
- Introversion: the 'internal', expanding ocean starts to contract and closes up again; or
- Extroversion: the 'exterior' ocean keeps expanding, closing an 'internal' ocean elsewhere.
In the first option, the Wilson cycle and the supercontinent cycle coincide, creating the possibility that the new supercontinent will have more or less the same dimensions as the old one. In the second option, the Wilson and supercontinent cycles do not coincide.
In their paper, the researchers line up and standardise the evidence for four well-known scenarios on future supercontinent formation:- The closure of the Atlantic Ocean, leading to Pangea Ultima;
- The closure of the Pacific Ocean, giving rise to Novopangea;
- The closure of both the Atlantic and Pacific Oceans, creating Aurica; and
- The closure of the Arctic Ocean, forming Amasia.
Pangea Ultima: keystone Africa
'Ultimate' Pangea would be a remake of the 'old' Pangea, more or less.
Credit: Pilgrim-Ivanhoe, reproduced with kind permission
'Ultimate Pangea' will come about via an introversion scenario, with the closing of the Atlantic and the re-formation of the 'old' Pangea – sort of. Introversion is the 'classic' scenario for supercontinent formation; in fact, Pangea itself was likely formed by introversion, with the closing of the Rheic and Iapetus Oceans.
Africa is the key continent here; first by colliding with Europe to form the new continent of Eurafrica, and ultimately as the keystone tying South and North America, Europe and Asia together. Remnants of the Atlantic and Indian oceans reincarnate as the 'ultimate' Mediterranean, closed off from the world ocean by East Antarctica.
Novopangea: Rift becomes Ocean
How Novopangea might come to be: the Pacific closes and a new ocean forms along the East African Rift.
Credit: Pilgrim-Ivanhoe, reproduced with kind permission
A 'classic' extroversion scenario leads to the closure of the Pacific Ocean, and to a 'new' Pangea – not just a re-forming of the old one. The East African Rift keeps growing, developing into a new ocean, replacing the Indian one. East Africa gets stuck against India's west coast.
Aurica: America in the middle
Two Wilson cycles in sync with a supercontinent cycle, and hey presto: Aurica.
Credit: Pilgrim-Ivanhoe, reproduced with kind permission
The Aurica scenario presupposes two Wilson cycles in sync with the supercontinent cycle. Both the Atlantic and Pacific Oceans close, helping to form the supercontinent of Aurica, with the Americas in the middle.
This requires the opening-up of at least one new ocean – for example, at a large rift along the present-day border between India and Pakistan. This new Pan-Asian Ocean, merged with the Indian Ocean, pushes these areas apart, turning them from next-door neighbors into lands on either side of Aurica.
Australia is now entirely landlocked, between Antarctica, East Asia, and North America. Europe and Africa have collided with the Americas from the other side. To the south, Madagascar stubbornly continues its separate course.
Amasia, the Arctic supercontinent
In the Amasian scenario, almost all continents would be joined 'at the top'.
Credit: Pilgrim-Ivanhoe, reproduced with kind permission
The Arctic Ocean closes. Almost all continents are joined at the 'top of the world', with the exception of Antarctica, the only one not drifting northward. It'll be a short hop from North America to North Africa, with Southern Europe acting as a land bridge in between. South America has repositioned itself, with its western edge against the eastern flank of North America.
These images produced by Pilgrim-Ivanhoe, reproduced with kind permission. Original context here. Images based on the aforementioned article: Back to the future: Testing different scenarios for the next supercontinent gathering, by Hannah S. Davies, J.A. Mattias Green and João C. Duarte, published in Global and Planetary Change (Vol. 169, October 2018).
Strange Maps #1064
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Dinosaur tracks in the ceiling of Castelbouc Cave in France.
French scientists found gigantic dinosaur footprints on the roof of the Castelbouc cave the Lozère region of southern France. A new paper outlines the discovery approximately 1640 feet under ground by the paleontologist Jean-David Moreau from the University of Burgundy–Franche-Comté and his colleagues.
The footprints likely belonged to an unknown species of titanosaur and were made 166 to 168 million years ago, in the Middle Jurassic Period. Titanosaurs, a group of long-necked, lizard-like sauropods, could be found all over the world in present day Africa, the Americas, Europe, and Australia. Among titanosaurs were the largest land animals to have ever existed, like the Patagotitan, which stretched 121 feet long and weighed 138,000 pounds.
The titanosaur Alamosaurus.
Credit: Bogdanov, 2006. Creative Commons.
Some of the 38 tracks found in France were as large as 4 feet long. They were likely made by three dinosaurs at the time when the area was on the surface, making up a muddy shoreline along which the giant creatures traveled. Over time, the site was buried by geological processes, with the tracks becoming moldings in the roof of a cave that's half a kilometer underground.
They were spotted as part of a caving expedition in December 2015 by the paper's authors. To find them, the scientists had to go down a narrow labyrinth of crawl spaces that often get flooded. The tracks were in a space about 260 feet long, 66 feet wide and 33 feet high.
Dinosaur tracks in the ceiling of Castelbouc Cave in France.
Credit: Jean-David Moreau et al./J. Vertebr. Paleontol.
Speaking to the French science magazine Sciences et Avenir, Jean-David Moreau explained that a caver "who was ahead of me turned to me and with the lamp of his helmet projected a grazing lighting on the ceiling which allowed to bring out the marks."
You can read the paper "Middle Jurassic tracks of sauropod dinosaurs in a deep karst cave in France," published in the Journal of Vertebrate Paleontology.
Excerpt from a 19th century map of the Paris Catacombs, showing the labyrinthine layout underground (in color) beneath the straight-lined structures on the surface (in grey).
Ancient mining areas below Paris for limestone (red) and gypsum (green).Credit: Émile Gérards (1859–1920) / Public domain
"If you're brave enough to try, you might be able to catch a train from UnLondon to Parisn't, or No York, or Helsunki, or Lost Angeles, or Sans Francisco, or Hong Gone, or Romeless."
China Miéville's fantasy novel Un Lun Dun is set in an eerie mirror version of London. In it, he hints that other cities have similar doubles. On the list that he offhandedly rattles off, Paris stands out. Because the City of Light really does have a twisted sister. Below Paris Overground is Paris Underground, the City of Darkness.
Most people will have heard of the Catacombs of Paris: subterranean charnel houses for the bones of around six million dead Parisians. They are one of the French capital's most famous tourist attractions – and undoubtedly its grisliest.
But they constitute only a small fragment of what the locals themselves call les carrières de Paris ("the mines of Paris"), a collection of tunnels and galleries up to 300 km (185 miles) long, most of which are off-limits to the public, yet eagerly explored by so-called cataphiles.
The Grand Réseau Sud ("Great Southern Network") takes up around 200 km beneath the 5th, 6th, 14th, and 15th arrondissements (administrative districts), all south of the river Seine. Smaller networks run beneath the 12th, 13th, and 16th arrondissements. How did they get there?
Paris stone and plaster of Paris
It all starts with geology. Sediments left behind by ancient seas created large deposits of limestone in the south of the city, mostly south of the Seine; and gypsum in the north, particularly in the hills of Montmartre and Ménilmontant. Highly sought after as building materials, both have been mined since Roman times.
The limestone is also known as Lutetian limestone (Lutetia is the Latin name for ancient Paris) or simply "Paris stone." It has been used for many famous Paris landmarks, including the Louvre and the grand buildings erected during Georges-Eugène Haussmann's large-scale remodelling of the city in the mid-19th century. The stone's warm, yellowish color provides visual unity and a bright elegance to the city.
The fine-powdered gypsum of northern Paris, used for making quick-setting plaster, was so famed for its quality that "plaster of Paris" is still used as a term of distinction. However, as gypsum is very soluble in water, the underground cavities left by its extraction were extremely vulnerable to collapse.
Like living on top of a rotting tooth: subsidence starts far below the surface, but it can destroy your house.Credit : Delavanne Avocats
In previous centuries, a road would occasionally open up to swallow a chariot, or even a whole house would disappear down a sinkhole. In 1778, a catastrophic subsidence in Ménilmontant killed seven. That's why the Montmartre gypsum quarries were dynamited rather than just left as they were. The remaining gypsum caves were to be filled up with concrete.
The official body governing Paris down below is the Inspection Générale des Carrières (IGC), founded in the late 1770s by King Louis XVI. The IGC was tasked with mapping and, where needed, propping up the current and ancient (and sometimes forgotten) mining corridors and galleries hiding beneath Paris.
A delightful hiding place
Also around that time, the dead of Paris were getting in the way of the living. At the end of the 18th century, their final destination consisted of about 200 small cemeteries, scattered throughout the city — all bursting at the seams, so to speak. There was no room to bury the newly dead, and the previously departed were fouling up both the water and air around their respective churchyards.
Something radical had to happen. And it did. From 1785 until 1814, the smaller cemeteries were emptied of their bones, which were transported with full funerary pomp to their final resting place in the ancient limestone quarries at Tombe-Issoire. Three large and modern cemeteries were opened to receive the remains of subsequent generations of Parisians: Montparnasse, Père-Lachaise, and Passy.
Who says stacking skulls and bones can't be fun?Credit: Rijin via Wikimedia and licensed under CC BY-SA 4.0
The six million dead Parisians in the Catacombs, from all corners of the capital and across many centuries, together form the world's largest necropolis — their now anonymized skulls and bones methodically stacked, occasionally into whimsical patterns. The Catacombs are fashioned into a memorial to the brevity of life. The message above the entrance reads: Arrête! C'est ici l'empire de la Mort. ("Halt! This is the empire of Death.")
That has not stopped the Catacombs, accessible via a side door to a classicist building on the Avenue du Colonel Henri Rol-Tanguy, making just about every Top 20 list of things to see in Paris.
An underground economy
However, while the Catacombs certainly are the most famous part of the centuries-old network beneath Paris, and in non-pandemic times draw thousands of tourists each day, they constitute just 1.7 km (1 mile) of the 300-km (185-mile) tunneling total.
Subterranean Paris wasn't just used for mining and storing dead people. In the 17th century, Carthusian monks converted the ancient quarries under their monastery into distilleries for the green or yellow liqueur that still carries their name, chartreuse.
Because the mines generally keep a constant cool temperature of around 15° C (60° F), they were also ideal for brewing beer, as happened on a large scale from the end of the 17th century until well into the 20th century. Several caves were dug especially for establishing breweries, and not just because of the ambient temperature: going underground allowed brewers to remain close to their customers without having to pay a premium for real estate up top.
Overview of the Paris Catacombs.Credit: Inspection Générale des Carrières, 1857 / Public domain.
At the end of the 19th century, the underground breweries of the 14th arrondissement alone produced more than a million hectoliters (22 million gallons) per year. One of the most famous of Paris' underground breweries, Dumesnil, stayed in operation until the late 1960s.
In that decade, the network of corridors and galleries south of the Seine, long since abandoned by miners, became the unofficial playground for the young people of Paris. They explored the fantastical world beneath their feet, in some cases via entry points located in their very schools. Fascinated, these cataphiles ("catacomb lovers") read up on old books, explored the subterranean labyrinth, and drew up schematics that were passed around among fellow initiates as reverently as treasure maps.
As Robert Macfarlane writes in Underland, Paris-beneath-their-feet became "a place where people might slip into different identities, assume new ways of being and relating, become fluid and wild in ways that are constrained on the surface."
Some larger caves turned into notorious party zones: a 7-meter-tall gallery below the Val-de-Grâce hospital is widely known as "Salle Z." Over the last few decades, various other locations in subterranean Paris have hosted jazz and rock concerts and rave parties — like no other city, Paris really has an "underground music scene."
Hokusai's Great Wave as the backdrop to the "beach" under Paris.Credit: Reddit
Cataphiles vs. cataphobes
With popularity came increased reports of nuisance and crime — the tunnels provided easy access to telephone cables, which were stolen for the resale value of their copper.
The general public's "discovery" of the underground network led the city of Paris to officially interdict all access by non-authorized persons. That decree dates back to 1955, but the "underground police" have an understanding with seasoned cataphiles. Their main targets are so-called tourists, who by their lack of knowledge expose themselves to risk of injuries or worse, and degrade their surroundings, often leaving loads of litter in their wake.
The understanding does not extend to the IGC. Unlike in the 19th century, when weak cavities were shored up by purpose-built pillars, the policy now is to inject concrete to fill up endangered spaces — thus progressively blocking off parts of the network. That procedure has also been used to separate the Catacombs to prevent "infiltration" of the site by cataphiles.
Many subterranean streets have their own names, signs and all. This is the Rue des Bourguignons (Street of the Burgundians) below the Champs des Capucins (Capuchin Field), neither of which exists on the surface.Credit: Jean-François Gornet via Wikimedia and licensed under
The cataphiles, however, are fighting back. In a game of cat and mouse with the authorities, they are reopening blocked passages and creating chatières ("cat flaps") through which they can squeeze into chambers no longer accessible via other underground corridors.
Catacomb climate control
Alone against the unstoppable tide of concrete, the amateurs of Underground Paris would be helpless. But the fight against climate change may turn the subterranean labyrinths from a liability into an asset — and the City of Paris into an ally.
The UN's 2015 Climate Plan — concluded in Paris, by the way — requires the world to reduce greenhouse gas emissions by 75 percent by 2050. And Paris itself wants to be Europe's greenest city by 2030. More sustainable climate control of our living spaces would be a great help toward both targets. A lot of energy is spent heating houses in winter and cooling them in summer.
This is where the constant temperature of the Parisian tunnels comes in. It's not just good for brewing beer; it's a source of geothermal energy, says Fieldwork, an architectural firm based in Paris. It can be used to temper temperatures, helping to cool houses in summer and warming them in winter.
One catch for the cataphiles: it also works when the underground cavities are filled up with concrete. So perhaps one day, Paris Underground, fully filled up with concrete, will completely fall off the map, reducing the city's formerly real doppelgänger into an air conditioning unit.
Cool in summer, warm in winter: Paris Underground could become Paris A/C.Credit: Fieldwork
Strange Maps #1083
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