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A new study conducted by the University of Maryland, Curtin University and the Geological Survey of Western Australia has found that the Earth’s original outer layer may have been a single, solid shell that later broke into what we know today as tectonic plates.
Published in the journal Nature, the study provides a possible conclusion to the highly-debated idea that tectonics plates have always existed.
To reach their conclusion, researchers collected basalt rocks and granites from the East Pilbara Terrane, a large area of ancient crust in Western Australia, where some of the oldest rocks in the world are found, according to Business Insider.
Phys.org reports that researchers specifically selected granites with a composition associated with volcanic arcs — a “telltale sign of plate tectonic activity.”
The team then performed a variety of thermodynamic calculations to understand more about the chemical composition of the samples.
Surprisingly, they found that the granites found at the East Pilbara Terrane had been melted in a way other than heat produced by subduction, which is observed in scenarios involving plate tectonics.
This meant that plate tectonics could not have been in play when the Pilbara granites formed.
“Our research suggests that the ancient granites in the Pilbara had not only parents, but also grandparents, and possibly great-grandparents before them,” said Tim Johnson, a geologist at The Institute for Geoscience Research at Curtin University and lead author on the study. “Such a protracted history is not compatible with subduction and modern plate tectonics.”
So, how did the Pilbara granites form?
To create the conditions necessary to transform the basalt rocks into granites (without subduction), Earth must have been incredibly hot very close to its surface at the time they were created.
The team concluded that such conditions were created by a complete layer of cooler rock that sat on top of a hotter layer of Earth’s crust, creating a stagnant lid or “egg shell” that trapped in heat and made the transformation possible.
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