from the I-feel-extraterrestrial-earth-move-under-my-feet dept.
The hypothesis could help in the search for other Earthlike worlds:
The leading explanation for the origin of the moon proposes that a Mars-sized planet, dubbed Theia, struck the nascent Earth, ejecting a cloud of debris into space that later coalesced into a satellite (SN: 3/2/18). New computer simulations suggest that purported remains of Theia deep inside the planet could have also triggered the onset of subduction, a hallmark of modern plate tectonics, geodynamicist Qian Yuan of Caltech reported March 13 at the Lunar and Planetary Science Conference.
[...] 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 focus on two continent-sized blobs of material in Earth's lower mantle known as large low-shear velocity provinces (SN: 5/12/16). These are regions through which seismic waves are known to move anomalously slow. Researchers had previously proposed these regions could have formed from old, subducted plates. But in 2021, Yuan and colleagues alternatively proposed that the mysterious masses could be the dense, sunken remnants of Theia.
[...] While the simulations suggest the large low-shear velocity provinces could have had a hand in starting subduction, it's not yet clear whether these masses came from Theia. "The features ... are a fairly recent discovery," says geodynamicist Laurent Montési of the University of Maryland in College Park. "They're very fascinating structures, with a very unknown origin." As such, he says, it's too early to say that Theia triggered plate tectonics.
"It's provoking. This material down there is something special," Montési says of the large low-shear velocity provinces. "But whether it has to be originally extraterrestrial, I don't think the case is made."
Q. Yuan. A giant impact origin for the first subduction on Earth. Lunar and Planetary Science Conference, The Woodlands, Texas, March 13, 2023.