The big picture of Earth’s geological history over the past 2 billion years shows continents coming together and then breaking apart about every 600 million years. A future reunion is inevitable, but geologists have long debated whether it will happen when the west coasts of the Americas meet Asia, or whether their east coasts reconnect with Europe and Africa. A new study concludes that fundamental changes have taken place deep inside the Earth, leaving only the earlier scenario possible.
A union of continents leaves most of the world to be taken up by a single vast ocean save for the occasional island. During the time of Pangea, the last universal supercontinent, this was known as Panthalassa. Once the continents begin to break up, the world has two or more major bodies of water – inner, surrounded by the expanding landmasses, and outer, into which the continents move. The Atlantic and Indian Oceans are the remnants of former inland seas, while the Pacific has become Panthalassa via the Outer Ocean.
New supercontinents can be created by the closure of the inner or outer oceans. At least, according to Professor Zheng-Xiang Li of Curtin University, this has been possible in the past. Now, however, Earth has reached a point where only outer oceans can be shut down, Li and co-authors conclude in a study published in the National Science Review, making the sinking of the Pacific inevitable.
The Atlantic is currently growing at a rate of a few centimeters per year while the Pacific is shrinking at a similar rate, making it easy to extrapolate the closure of what is now the world’s largest ocean basin. Geologists have done this before, naming it Amasia, which Li told IFLScience will take 280 million years to form from parts of Pangea at current speeds. In the past, however, such trends have sometimes reversed, with the continents coming together again like an accordion to close the inner ocean again.
That, according to the paper, is no longer possible. The authors’ modeling suggests that continental movements are highly dependent on the strength of the oceanic crust between them. Only when the crust is strong can continents change direction and rejoin across young inner oceans.
As the mantle cools, the oceanic crust formed on it has thinned and thus weakened. Li and co-authors found that about 540 million years ago, Earth’s temperature cooled enough to weaken the crust to a point where such reversals can no longer occur. Therefore, Amasia – and indeed all future supercontinents – will be formed by crossing the outer ocean.
Along with America’s westward march and Asia’s eastward migration, Australia will move northward until colliding with Indonesia and being carried into what is now the South Pacific.
Antarctica has long been anchored at the end of the world, but Li told IFLScience that its future movements are “hard to tell.” Still, he thinks it’s very likely that it will also make its way into the Pacific, adding that a zone to which it can cross “appears to be forming already towards New Zealand.”
Some previous predictions suggested that Amasia would converge around the North Pole, creating an enormous ice cap and cooling the planet. However, Li told IFLScience that the latitudes of the larger continents are unlikely to change. This does not mean that the earth will remain as hospitable as it was during our evolution.
“Earth as we know it will change drastically as Amasia forms. Sea levels are projected to be lower and the supercontinent’s vast interior will be very dry with high daily temperature ranges,” Li said in a statement.
The work is published in National Science Review.
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