Do continents merge to form a supercontinent?

If the planisphere hanging over your desk seems like it has never changed, at least not since your earliest memories, the map of the world is not meant to look like this forever.

Carefully carved continents anchored in the oceans; islands scattered in the middle of the seas, screwed to their geographical coordinates? Nope. The reality is actually enough to make you dizzy. It is true that, on a human scale, the face of our planet has changed little or not at all. However, the continents have indeed been in constant motion since the formation of the Earth 4.5 billion years ago, causing major changes in our world’s history.

The world map is constantly changing

Pangea is the most popular visualization. It is indeed the last supercontinent to form on Earth’s surface, about 300 million years ago, before the terranes drifted and assumed the configuration known to them today.

“We know that there have been other supercontinents in Earth’s history: Rodinia [qui s’est scindé] 750 million years ago, Columbia 1.5 billion years ago, It mentions Nicolas Coltis, director of research in the department of geosciences at the École Normale Supérieure in Paris. It seems that every 500 million years a supercontinent forms and then breaks up. These are opening and closing cycles, but they never occur in the same way.

So don’t expect a systematic movement of continents that always diverge at the same places and join endlessly at the same points. The map of the world is constantly changing, as American geologist Christopher Scott tries to reconstruct it in predictions that remain hypothetical.

However, if the movements of the continents are confirmed, the researchers emphasize that it is difficult to determine them precisely. Scientific methods allow us to accurately reconstruct a picture of the Earth over the past 300 million years, but remain limited when we go back in time.

Convection, subduction and a pot of milk

To understand why continents move, we need to talk about plate tectonics. Tectonic or lithospheric plates make up the outer hard part of the Earth, namely (to oversimplify) our continents and oceans. “Plate tectonics is the process by which the Earth cools, the plates move to release heat”, explains Laurent Husson, a geologist at the Institute of Earth Sciences. Indeed, the plates move due to the convection of the mantle, that is, due to heat transfers in this inner part of the Earth located before the core.

“Let’s imagine a pot of milk that boils and forms a harder milk crust on the surface.the scientist schematizes. This is convection. It is the entire mantle that flows and through it carries its continents as dirt that has accumulated on the surface of the planet., which prevents convection from working properly. Since continents make up one-third of the Earth’s surface, if they were all packed into a supercontinent, they would form a thermal blanket that prevents the heat from escaping the mantle. It accumulates until it becomes hot enough to weaken the continents, break them into pieces, and create an ocean that allows this heat to escape.

If continents are therefore thermal insulators, oceans allow them to reject heat. Thus, the grouped continents are doomed to break up to empty this furnace: Pangea thus broke up, separating the Americas from Eurasia and Africa by the Atlantic Ocean. Opening up, the ocean then pushes the land on either side, causing new movements and forcing the continents to one day come together. Convection thus breaks up the regions, pushes them apart and joins them into a supercontinent before starting again.

A phenomenon within this convection, in particular, allows the movement of continents. It’s time to come up with another word: subduction. The plates on which the continents float consist of oceanic ridges on one side and subduction zones on the other. At the level of ocean ridges, heat is released in the oceans: it is a hot place.

The further away the material is from these ridges, the colder and therefore heavier the material becomes, these are the subduction zones at the end of the plates. This is where one heavier plate falls under another and the continents on the surface collide, this is a collision. “A priori, subduction is the main engine of continental movement”says researcher Nicholas Koltis.

Cruise speed

With their strength, subductions are the main factor in the rate of rotation of the continents. But they are not applied in the same way on every plate, creating quite significant rhythm variations from one plate to another.

“Some continents are moving very fast, exceeding ten centimeters per year. These are those on the plate in complete subduction, such as Australia, which evolves 10 cm per year, or India, which moves very quickly even before entering the Himalayas.Nicolas Coltice explains. We stay within these orders of magnitude over time. This is the rate of growth of nails and hair, forming an image of it.

This phenomenon is observed even in certain specific situations on our scale. For example, the bridge between Rion and Antirion, which connects the Peloponnese and Greece, was built at the junction of two tectonic plates, which are the source of many earthquakes and move a few millimeters apart each year. Therefore, the building is designed to move up to 2 meters at the same time.

According to the researchers, a sudden acceleration of these continental movements is very unlikely. The balance of forces that has existed for billions of years is almost always stable and unaffected by human activity. “A continent moving 1 cm per year will not suddenly increase to 1 km per year., describes the geodynamist. The Earth’s mantle is a large rock that is difficult to move. Only a giant meteorite at least the size of the Moon could change everything by crashing into the Earth.

However, continents experience accelerations and decelerations depending on different periods of history. “We talked about driving forces, but there are also resisting forces. The movement of the continents has slowed down a lot over the past 100 million years because there have been so many collisions.Laurent Husson says. This is an obstacle to the free circulation of the plates: the more collisions between continents we have, the more obstacles we have, the more it slows down the whole.

Dangerous collisions?

When continents collide, they form huge mountain ranges that change the face of our planet. The Indian plate is a good example of this: after moving rapidly towards Eurasia due to its driving force, it collided with the continent and thus created the Himalayas as a witness of this collision.

“It’s hard to talk about wildness, because this phenomenon stretches back hundreds of thousands of years or more. It’s not like a car accidentNicholas Koltis emphasizes. Despite everything, the collisions are realized by folding rocks, faults and therefore earthquakes, changes in terrain and thus climate changes. This inevitably disturbs the environment of the surface.

Don’t panic, a massive breakout caused by these moves is not expected. These events occur over such a long period of time that living things have time to adapt. According to scientists, this is more a factor in the diversification of life. “When continents are together, they create bridges for life, and then when they separate, certain populations are isolated and must evolve. But the more diverse life is, the stronger and richer it is., the researcher confirms.

A map of the future

Although not felt on the scale of our lives, these collisions and upheavals of our environment are happening right now. “Africa collides with Europe to form the Alps, the Himalayas are still being built, and even Australia collides with all of Indonesia.Nicholas Koltis notes. We unite a very large continent. The question is, what will happen between this continent and the American side?

Under the most realistic assumptions, America could continue westward and block the Pacific Ocean, or retreat and block the Atlantic Ocean. If Laurent Husson is to be believed, the world on our side will be the end of the story: “The convergence is almost completethe geologist assures. Africa and Europe already touch in several places, for example in Gibraltar: even if it is the Mediterranean, we collide! It might be a little bit of closure, but it’s not a breakup, even if it lasts for a long time. You have to understand that the puzzle isn’t necessarily going to be perfect.”

Future predictions are more complicated. “There is a prediction limit. It’s like the weather, you can’t see the last 100 million years, and that’s probably not enough to predict the next supercontinent.”, warns geodynamicist Nicholas Koltis. Pangea broke up only 200 million years ago. A grain of sand on the planet’s time scale. Despite everything, Pangea Proxima has already been carefully studied by a number of scientists, such as the American Christopher Scott, who made a futuristic map of our Earth. Unfortunately, we will no longer be here to verify its accuracy.

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