Fifty million to 200 million years from now, geologists expect Earth's continents to smash together into one big supercontinent, just as they've done repeatedly in our planet's distant past — and a new computer model suggests that the Arctic Ocean and Caribbean Sea will be among the first things to go.
That hasn't been the conventional wisdom: In the past, scientists have assumed that either the Atlantic Ocean will close up, reversing the trend that broke apart the last supercontinent ... or that the current spreading zone in the Atlantic will push the continents 180 degrees around the world to close up the Pacific instead.
The third possibility, outlined in this week's issue of the journal Nature, goes in a different direction.
"Our model says that with every supercontinent cycle the whole arrangement needs to be shifted 90 degrees. So it's quite a shift." Yale geologist Ross Mitchell told me. "A tectonic shift."
The model is based on an analysis of the magnetism of ancient rocks. Mitchell, a doctoral student at Yale, took on the project with fellow student Taylor Kilian and Professor David Evans, the Nature paper's senior author. The rocks record how the orientation of Earth's continental plates has changed with respect to the magnetic poles over billions of years, and the researchers looked for the characteristic back-and-forth magnetic signature of a supercontinent taking shape.
"By identifying these back-and-forth motions around a stable axis, we had a measure of the center of that axis," Mitchell said. "All we had to do was find continents which had that axis from two successive supercontinents, and you could measure the angle between two successive axes."
The readings from the rocks were fed into a computer program that could essentially wind the clock back on the crashes that formed past supercontinents, as well as the smashes that broke them apart. Scientists say that there have been at least three supercontinents in Earth's distant past: Pangaea, which goes back 300 million years; Rodinia, which dates to roughly 1 billion years ago; and Nuna, which existed about 1.8 billion years ago.
Mitchell and his colleagues saw a pattern where rocks on the edge of one supercontinent became the central point for the next. That translates roughly into a 90-degree angle on the globe. For Pangaea, the central point was in present-day Africa. The newly published model, known as the orthoversion model, suggests that the central point for the next supercontinent, known as "Amasia," will be around the present-day North Pole.
The model shows North and South America pushing together to close up the Caribbean. North America would be drawn along the Pacific "Ring of Fire" to crash into Eurasia and close the Arctic Ocean. The Mediterranean Sea would disappear when Africa smashes into Europe. Australia would continue its current northward drift, becoming part of Asia somewhere between India and Japan. Antarctica, meanwhile, would be left out of the supercontinent, at least at first.
"We'd probably have a thick ice cap at the center of the supercontinent," Mitchell said. But Amasia wouldn't stay frigid. The model suggests that the supercontinent would twist around to bring more of its land mass closer to the equator.
The model can't set a time frame for the creation of Amasia, but it looks as if the continental cycle is quickening somewhat, based on the rise and fall of past supercontinents. That leads the Yale researchers to suggest that Amasia will take shape during the next 50 million to 200 million years.
'A leap ahead'
J. Brendan Murphy, a geologist at St. Francis Xavier University in Nova Scotia, said the Nature paper "provides a unified and plausible explanation of events that for many of us are enigmatic."
"It is certainly a leap ahead in the debate," he said, but he added that the debate is far from over.
"As you go deeper into time, the database, like most things in geology, becomes less reliable. ... We really need more accurate data for the episodes that they're talking about," he said.
A more thorough analysis of magnetic rocks could provide more evidence to support the orthoversion model, or knock it down. It might even turn out that continents can follow a variety of models to bunch up into supercontinents. "Even if the model doesn't stand up to the test of time, we'll learn a lot by testing it," Murphy said.
Mitchell told me that learning more about the clash of continents can provide insights into the migration of biological species over the course of deep time. For example, the rise and fall of Pangaea played a key role in the dispersal and specialization of species across the world. But it's impossible to predict how the rise of the next supercontinent will affect Earth's future inhabitants.
"I would be quite surprised if humans lasted long enough to see the next supercontinent come to fruition," Mitchell said. "The truth is that none of the present scientific community will be around 100 million years from now to test these models."
More about tectonic shifts:
- Flash interactive: Earth's timeline
- Upside-down mountain revealed inside Earth
- Plate tectonics could be essential for alien life
- Rock links Antarctica and North America
Mitchell, Kilian and Evans are co-authors of "Supercontinent Cycles and the Calculation of Absolute Palaeolongitude in Deep Time." The research was supported by the National Science Foundation.
Alan Boyle is msnbc.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter or adding Cosmic Log's Google+ page to your circle. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for other worlds.