for National Geographic News
Supercontinents can form when a huge plume of hot rock from deep inside Earth wells up between the continental plates, pushing them apart until all Earth's landmasses collide.
This is the finding from a new study that suggests—contrary to accepted theory—that such a process formed the supercontinent Pangaea 300 million years ago. Today's continents are thought to have formed from Pangaea's gradual breakup.
Earth's shifting plates have been forming and breaking up supercontinents for billions of years, scientists believe, and traditionally they thought that suction is the driving force. (See an interactive map of Earth's tectonic plates.)
In seismically active places such as the Ring of Fire in the Pacific region, slabs of Earth's crust descend into the interior in a process called subduction.
This creates a downward current that sucks the continents into collision above it, like soapsuds being drawn together as water flows down a drain.
But in the new paper, J. Brendan Murphy of St. Francis Xavier University in Nova Scotia, Canada, and colleagues suggest that a plume of subducting crust in the middle of the ancestral Pacific Ocean descended so deeply it hit Earth's core.
Superheated, it then rebounded like a bubble in a boiling pot. That produced a superplume strong enough to push, not suck, the ancient continents back together and form Pangaea.
Peter Cawood, director of the Tectonics Special Research Centre at the University of Western Australia, called the finding "excellent and stimulating."
"Although provocative, I believe it is probably right," Cawood said by email.
Matching up rock types, examining magnetic signatures, and cataloging fossils have allowed scientists to trace the cycle of supercontinents forming and breaking apart back at least a billion years. Earth is believed to be about 4.5 billion years old.
The data show there were two supercontinents before Pangaea called Rodinia and Gondwana that formed and broke up hundreds of millions of years ago.
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