THE WOODLANDS, TEXAS — Vestiges of a moon-forming cataclysm could have kick-started plate tectonics on Earth.
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.
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The story offers a cohesive explanation for how Earth gained both its moon and its moving tectonic plates, and it could aid in the search for other Earthlike worlds. But others caution that it’s much too early to say that this is, in fact, what happened.
Of all the worlds yet discovered, ours is the only one known to have plate tectonics (SN: 1/13/21). For billions of years, Earth’s creeping plates have spread, collided and plunged beneath one another, birthing and splitting continents, uplifting mountain ranges and widening oceans (SN: 4/22/20, SN: 1/11/17). But all this reshaping has also erased most of the clues to the planet’s early 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 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…
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