A New Theory Offers an Explosive Explanation for Earth's Mysterious Blobs
Among the inner solar system, Earth is the only planet that experiences plate tectonics.
A new study, using convection models, shows that Earth’s collision with the protoplanet Theia some 4.5 billion years ago, might’ve triggered early subduction in Earth’s crust.
This theory joins a cadre of other ideas describing the origin story of plate tectonics, an important process that formed the planet's landmasses.
In the early days of the solar system, Earth as we know it today would’ve been completely unrecognizable.
For one, its surface was likely a roiling pool of molten magma, a hellish scene for a geological eon fittingly known as the Hadean, and the Earth was moonless—that is, until the dwarf planet Theia made its explosive introduction. Some 4.5 billion years ago, only 100 millions years or so after the Earth first formed, Theia crashed into Earth, creating a cataclysmic display that’d make the impact of the dino-killer asteroid Chicxulub look like a nice afternoon.
As the hypothesis goes, from the chaos of this collision coalesced Earth (and the Moon), and pieces of that ancient smash up are still buried deep in Earth’s lower mantle in two large blobs known as low-shear-velocity provinces, or LLVPs. In 2023, Caltech’s Qian Yuan published a study detailing how these mysterious blobs formed over billions of years of mantle convection, and now Yuan is back with a new study, published in the journal Geophysical Research Letters, exploring how Theia may also be responsible for our planet’s plate tectonics, the geologic forces of subduction and collision that formed the Earth’s landmasses.
“Plate tectonics remains unique to Earth, but when and how it started is debated,” Yuan and his co-authors write in the study. “Earlier studies indicate that the core-mantle boundary (CMB) temperature is increased due to accumulation of the impactor's core during the impact…We perform whole-mantle convection models to illustrate that strong mantle plumes can arise, weaken the lithosphere, and eventually initiate subduction ∼200 Myr after the giant impact.”
Among the inner rocky planets of our Solar System—Mercury, Venus, Earth, and Mars—our planet is the only one with any form of plate tectonics, so understanding this process, when it began, and how it impacts the habitability of a planet is important. Scientists aren’t exactly sure when plate tectonics began, and estimates range wildly from 4.2 billion years ago to just only 85 million years ago, according to the Scripps Institution of Oceanography, but the general consensus places its beginning at around the 3 billion years old mark.
However, in this new study, Yuan and his colleagues used complex convection models to show how early subduction, a major process of plate tectonics, could’ve gotten started only 200 million years after the Theia-Earth collision, roughly 4.3 billion years ago. This is roughly in line with previous evidence of Hadean detrital zircons that show geochemical signals of early subduction. This means that when the CMB heated up due to Theia’s collision, it sent strong mantle plumes toward the lithosphere, the outermost rocky shell of the planet, which weakened it and kickstarted subduction.
While this theory contains strong evidence, it’s only one among many theories as to how Earth’s plates formed—whether Earth expanded and cracked its rocky shell, or was otherwise ripped apart by gravitational forces. But as scientists continue to uncover mysteries surrounding this geologic process unique to our planet, they’ll also learn just how vital it is for sustaining complex life on distant worlds.
You Might Also Like
