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Big earthquakes remind us that the earth's continents aren't sitting still. They're moving, slowly but inexorably, across the globe. In fact, there have been times when all the continents have come together to form a single supercontinent.

NPR's Richard Harris reports now on the study in the journal Nature that suggests how the next supercontinent will come into being.

RICHARD HARRIS, BYLINE: You can think of continents as giant puzzle pieces shuffling around the Earth. When they drift apart, mighty oceans form. When they come together, oceans disappear and it's all because continents sit on moving plates of the Earth's crust.

ROSS MITCHELL: Continents on these plates typically move, I would say, about the rate your fingernails grow.

HARRIS: Ross Mitchell, a graduate student at Yale University, says that adds up to a lot of motion over hundreds of millions of years. Look at an atlas and you can imagine how Africa and South America, for example, once nestled together.

MITCHELL: Rewind the tape and bring all the continents back into their jigsaw arrangement, you have kind of this vast land mass of all the Earth's continental blocks together.

HARRIS: Last time all the land mass clumped up, it formed a supercontinent called Pangaea. The dinosaurs walked there, but Pangaea wasn't the first.

MITCHELL: There had been three - possibly a debated fourth - supercontinent through the billions of years.

HARRIS: Mitchell has been studying that deep history by looking at tiny magnets buried in rock around the world. Those magnets pointed north when they were locked into the rock. Sample those magnets in layers of rock laid down over millions of years and you can tell the story of how those continents have moved.

And, naturally, that led Mitchell to wonder what the next supercontinent will look like. There have been two leading ideas. One is that the continents will collapse together again at the site of the last supercontinent, centered on Africa. That would squeeze the Atlantic Ocean shut.

The other idea is that the Atlantic would keep on growing and growing.

MITCHELL: A supercontinent rifts apart and the continents skirt around to the opposite side of the globe, recreating the next supercontinent 180 degrees on the opposite side of the globe from the previous one.

HARRIS: That would leave us with a supercontinent in place of the Pacific Ocean, but Mitchell's research for his PhD thesis suggests both of those ideas are wrong. Instead, he says the continents seem to be moving north. That means the Caribbean Sea and the Arctic Ocean will be squished shut.

MITCHELL: Think about closing the Caribbean Sea. You've now fused North and South America. And then by fusing the Arctic Ocean, you would suture the Americas with Eurasia.

HARRIS: That would create a supercontinent called Amasia that would form at the top of the Earth. Antarctica might remain isolated at the bottom of the world.

Brendan Murphy studies supercontinents at St. Francis Xavier University in Nova Scotia. He says the Yale team's idea is provocative, innovative and plausible.

BRENDAN MURPHY: What they've done is they've thrown another possibility out there that, quite frankly, many of us hadn't really thought about. And so, even if the model is wrong, we'll all learn a lot by testing it.

HARRIS: And he says the challenge isn't simply finding different ways to put together the earth's jigsaw puzzle continents.

MURPHY: This is really important because it influences the evolution of our entire planet, including life that lives on it. For example, many people believe that supercontinents form and split apart. There are fundamental changes in climate.

HARRIS: Of course, the next supercontinent isn't likely to form for another hundred million years or so. And Mitchell says the human species will probably be long gone by then. So we won't know.

MITCHELL: But, you know, it's certainly fun to think about it.

HARRIS: And no one can disprove your PhD thesis.

MITCHELL: You figured me out before my advisor did.

HARRIS: Richard Harris, NPR News.

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