FORESTS, TEXAS – Traces of the moon formed by the cataclysm began to kick the tectonic plate on the Earth.
The primary explanation for the origin of the moon proposes that the large planet Mars called Theia struck the nascent Earth, sending a cloud of debris into space, which later coalesced into a satellite (.SN: 3/2/18). New computer simulations suggest that the remnants of Theia carried deep into the center of the planet could have also triggered a subduction attack, a sign of modern plate tectonics, Caltech geodynamicist Qian Yuan reported March 13 at the Lunar and Planetary Science Conference.
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The story provides a coherent explanation of how Earth got both its moon and its own moving tectonic plates, and may aid in the search for other terrestrial worlds. But others foretold much that this should be, indeed, what happened.
Of all the worlds yet to be discovered, ours is the only one known to have plate tectonics.SN: 1/13/21). For billions of years, the Earth’s plates have expanded beneath each other, collided and submerged, giving birth to and splitting continents, elevating mountain ranges and widening the seas (SN: 4/22/20, SN: 1/11/17). But all this reform has also erased most of the clues to early planetary history, including how and when plate tectonics first began.
Many hypotheses have been proposed to explain the initiation of subduction, a tectonic process in which one plate slides under another.SN: 5/2/22; SN: 6/5/19; SN: 1/2/18). Yuan and his colleagues chose to identify two groups of material in the Earth’s lower mantle that are known to shear at high speeds in low-lying regions (. )SN: 5/12/16). These are regions through which seismic waves are known to slow down anomalously. Researchers had previously proposed that these regions could be formed from subducted plates. But in 2021, Yuan and colleagues proposed, on the contrary, that the mysterious masses could be the dense, depressed remnants of Theia.
Building on that previous work, the researchers used computers to simulate how Theia’s impact, and its delayed remnants, would impact the flow of rock inside Earth.
They found that once these alien flowers sank to the bottom of the mantle, they were able to force large plumes of warm rock to rise up and wedge them into the rigid mantle of the Earth. As the swelling fed into the plumes, they lifted and pushed the Earth’s surface plates beneath them, triggering subduction about 200 million years after the moon formed.
While the simulations suggest that high-velocity low-shear regions may have had a hand in initiating subduction, it is not yet clear whether these masses originated from Theia. “Flowers … are the most recent discovery,” says geodynamicist Lawrence Montési of the University of Maryland at College Park. “They are very fascinating structures, of unknown origin. As such, he says, it is premature to say that Theia uses a tectonic plate.
“It is scratched. There is something special about this material,” says Montési of the large low-speed shearing supplies. “But I don’t think the case has been made whether it’s an extraterrestrial in the beginning.”
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However, if confirmed, the development could have implications that reach beyond our solar system. “If the moon is big, the impactor is likely to be big,” Yuan said. Scientists have yet to confirm the discovery of such an exomoonSN: 4/30/19). But keeping an eye out, Yuan said, could help us discover another world as tectonically active as our own.
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