Supercontinent Pangaea Pushed, Not Sucked, Into Place

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(The older supercontinent called Gondwana is different from the southern landmass known as Gondwanaland that formed 200 million years ago as Pangaea split apart.)

Wouter Bleeker, of the Geological Survey of Canada, has dubbed this cycle "the pulse of the Earth."

Murphy agrees. "Most people believe that for at least the last two and a half billion years, the Earth's history has been dominated by the amalgamation, breakup, and reforming of supercontinents," he said.

"It really is an underpinning of the evolution of the planet."

Accordion Action

But according to Murphy's new study, published this month in the journal Geology, there's something wrong with the suction-driven model in the case of Pangaea.

The problem, he said, is that it's very clear from the geologic record that the formation of Pangaea from the fragments of Gondwana occurred in two stages.

First Gondwana split, producing a steadily widening "young" ocean in its heart, much like the Atlantic Ocean that now separates the fragments of Pangaea.

Then something shifted. Rather than continuing to widen, as it would if its motion was being driven by suction, the new ocean started to shrink. The continents reversed course and slammed back into each other to form Pangaea.

This accordionlike action, dubbed the Wilson Cycle, has been recognized for more than 40 years, but the forces responsible for it are unknown.

Moreover, if current models thought to be responsible for these movements were applied to a 500-million-year-old Earth, they would not produce Pangaea in the right configuration.

Why this reversal happened is unclear, and that's disconcerting, Murphy said, because even though Pangaea is the best studied of the supercontinents, "something happened that we don't understand."

(Related: "Ancient Imbalances Sent Earth's Continents 'Wandering'" [April 7, 2008].)

The new theory of a superplume interfering with the suction process could put the pieces of what occurred into place, although more data would be needed to cement the idea.

"It's speculative," Murphy said. "What we'd like people to get out of the article is that there's a fundamental problem in understanding how Pangaea formed."

Earth's Future

Murphy added that his theory could have implications for the long-term future of the planet.

Right now the continents are converging on the mid-Pacific Ocean, where, if present motions continue, they will collide into a new supercontinent in about 75 to 80 million years.

But if Murphy's study is right, the process could reverse. North America could be driven back toward Europe, as happened in the formation of Pangaea.

Such a scenario, once thought unlikely, makes Earth's future a lot more fun to study, Murphy added.

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