JOHN DANKOSKY, HOST:
Continents are constantly moving across the Earth's surface, like big ships at sea. Several times in the Earth's history, they've smashed into each other to form supercontinents, only to - then break apart into smaller pieces millions of years later. Judging from history, can we say that millions of years from now, the world will be one giant continent again? And where will those puzzle pieces fit together? Now, geologists have predicted the next supercontinent, Amasia, will be created when the Americas and Eurasia fuse together.
But what does that mean? Does it mean we'll lose the Atlantic Ocean, the Pacific? Well, in a study in Nature this week, researchers say they developed a new model to predict Amasia's location. It challenges existing theories and gives us a lot to think about when it comes to what the world will look like a long time from now. Ross Mitchell is a doctoral student in geology and geophysics at Yale University. He's co-author of the study in Nature. He joins us from New Haven, Connecticut, today. Welcome to SCIENCE FRIDAY.
ROSS MITCHELL: Hi there, John.
DANKOSKY: So what do we know about the last supercontinent that existed - Pangaea?
MITCHELL: Well, actually, I was just wondering - and I'm sure if Ira wouldn't mind - if you and I could call this the segment of the show this afternoon where we'll live along - on the topic of future supercontinent Amasia. But to your question, Pangaea, you know, took form about 300 million years ago. And when we look around the globe today, we see the kind of, you know, seven continents that we're familiar with. And these seven continents do fit into this kind of jigsaw arrangement, where we to rewind the tape backwards and close kind of these interior oceans, like the Atlantic Ocean, that opened up and ripped it apart, Pangaea.
But truth is, is over the last few decades, we've begun to realized that Pangaea's actually only the most famous and latest supercontinent of several throughout our history. In fact, there seem to be at least three supercontinents throughout Earth history, and possibly a debated fourth.
DANKOSKY: Do we know what those ones look like?
MITCHELL: We have developed, you know, ideas for sure. So before Rodinia - I mean, before Pangaea 300 million years ago, there was Rodinia about one billion years ago. And even before that, there was Nena, 1.8 billion years ago. And, actually, only recently have we began to - have we been able to reconstruct even just a core of that first - possibly first supercontinent Nena. So indeed, you know, the various puzzle pieces remain to be put together. But hopefully now, we may have a dominant theory that will allow us to figure out how those puzzle pieces will fit in.
DANKOSKY: Well, why don't you tell us about your theory? And put it in the context of the other theories that are out there about what the next supercontinent's going to look like. What are the options that we have?
MITCHELL: Well, that's right. There were kind of two competing and quite opposing models, quite frankly, that were available to us, both of which had evidence to support them. They were termed the introversion and extraversion models, referring to personalities, trying to humanize the topic a little bit. And what the introversion model stipulated was that, as continents rift apart, they'll actually kind of collapse back in on themselves, recreating the future supercontinent more or less where the previous supercontinent was.
The extraversion model, the competing model couldn't be more opposed. In fact, that stipulated that the continents rifting away would actually skirt all the way to the opposite side of the globe, 180 degrees away from where the previous supercontinent was. So these two previous models did place predictions for future supercontinents at either zero or 180 degrees, at opposite ends of each other.
DANKOSKY: So now your theory is something entirely different here. This is where everything, what, moves to the top of the Earth?
MITCHELL: That's right. We find that it - when we look at the historical record of supercontinent cycles, we find the answer seems to be right, kind of somewhere smack-dab in the middle. And to be clear, we're not exactly proposing a kind of fuzzy combination of the two previous models. In fact, what we're saying quite precisely is that 90 degrees - within statistical significance - seems to be the angle at which a supercontinent will secede the one before it.
What that kind of means, thinking about it, is, you know, what does a quarter of the globe mean? If you kind of envision a supercontinent encapsulating about a half a hemisphere, you know, sitting nestled on the equator, as continents would break off that supercontinent, what we're saying is that the continent will travel only until it meets the edge of that supercontinent, which is actually encircled - the supercontinent is encircled by subduction zones. Today, we call this Ring of Fire. And that's actually where most volcanic and seismic earthquake activity occurs around the Earth today. And so it's at the edge of previous supercontinents that we propose future supercontinents to nucleate.
DANKOSKY: So what does this mean - if you can draw a picture for people in their minds, what does this mean the Earth will look like if this takes place millions of years from now?
MITCHELL: Right. Well, I would alert your listeners to, you know, scifri's webpage because we do have several, hopefully, striking visuals, not only a video of the past 500 million years documenting the rise and fall of, you know, the latest supercontinent, Pangaea, but we also do predict what this future supercontinent Amasia will look like. And because we kind of now have a firm grasp on what and how supercontinents might take form, it is kind of warranted to take at least a fun, speculative look at what the future supercontinent Amasia would look like.
And now, Amasia is not a new name. In fact, the introversion, extraversion models, you know, each had their own way of leading to Amasia. What's new here is that what we're saying is that Amasia will take form in a different place than expected. And what we say is that if you look 90 degrees away from the center of the previous supercontinent Pangaea - which is more or less where present day Africa sits today - if you look 90 degrees away from there, which ocean basins do you find to be the future sites of continent collisions? Now, the reason I mentioned ocean basins is because the oceans are kind of transient features on Earth's surface, and it's ocean basins that are subducted and pushed beneath plates when two converge. So we would predict ocean basins to close.
And when we look 90 degrees away from Africa, we find the Caribbean Sea and the Arctic Ocean. Now, if you think about it, John, if we were to close the Caribbean Sea, we would fuse the North and South America - the Americas together. And where you to fuse - where you to close the Arctic Ocean, you would suture the, kind of, the Americas in a mutual north migration with Eurasia.
MITCHELL: And, in fact...
DANKOSKY: ...I just have to ask: But then what happens beneath all of that? I mean, what happens to Antarctica? Does it just stay there by itself?
MITCHELL: Excellent question. Actually, just looking - even without knowing kind of this overarching model of 90 degrees, what we call orthoversion, even without knowing that model, we could take a look at kind of present day plate motions and imagine what they would look like if we were just to extrapolate them into the immediate future. And African, for example, we know is on a collision course for Europe, one day soon to make the Mediterranean mountains, if you will, the Mediterranean Sea.
But we still - in the Americas and Eurasia and Africa amalgamation - have Antarctica to think about, as you mentioned. And actually some recent work, just a few months ago, suggested that Antarctica may actually remain stranded and, unfortunately, be a loner in this next supercontinent cycle. But in our model, at least we do propose that Australia will continue its northward motion and join the Asia amalgamation eventually some day somewhere, probably between present day Japan and India.
DANKOSKY: Well, as he said before, you can find out more at sciencefriday.com. There's an awful lot of interesting visuals there, and that's a better way to maybe understand what this world is going to look like. Very, very quickly, Ross: millions of years from now? How long is it going to take?
(SOUNDBITE OF LAUGHTER)
FLORA LICHTMAN, BYLINE: Excellent question. Yeah, I keep using the phrase supercontinent cycle, but the truth is it's not exactly as predictable as cycles you and I are familiar with, like the seasonal cycle, for example. But there are some clues from Earth's past that do key us in. In fact, the supercontinent cycle seems to be speeding up. That...
DANKOSKY: Well - and I've got to leave there, Ross. But we'll wait around for it. Ross Mitchell is a doctoral student in geology and geophysics at Yale University. Thank you so much.
MITCHELL: Thanks for your patience.
DANKOSKY: I'm John Dankosky, and this is SCIENCE FRIDAY, from NPR. Transcript provided by NPR, Copyright NPR.