On the scale of favorable to cataclysmic events, the massive impact of a Mars-sized object that slammed into Earth about 4.5 billion years ago ranks pretty high: it’s thought to have set our planet’s cracked, rocky crust in motion , new research shows.
The impact of Theia, the fist in question, is also believed to have ejected debris from previous work that coalesced into the moon and populated Earth with essential elements for life. But its possible role in creating plate tectonics, the chunks of crust that jiggle atop our planet’s sediment, is far less certain.
It wasn’t until last year that scientists found evidence of what they suspect with greater confidence to be remnants of Theia inside Earth to match those inside the Moon.
First discovered in the 1980s, these continent-sized patches beneath the Pacific Ocean and Africa were previously thought to be either temperature hotspots or a magma “ocean” deep beneath our watery, or old , submerged tectonic plates. These scenarios were considered more plausible than the remains of Theia surviving billions of years in a shaken mantle.
Now, a new study by researchers at the California Institute of Technology (Caltech) suggests that Theia may be the cause of the turbulence of the same mantle and the movement of tectonic plates on its surface.
“The giant impact is not only the cause of our moon, if this is the case, it also determined the initial conditions of our Earth,” Caltech geoscientist Qian Yuan, who led the study, said The Washington Post.
After leading the 2023 study describing how part of Theia might have sunk to Earth’s core after the impact and survived to the present day, Yuan and his colleagues at Caltech set out to figure out what happened next.
Evidence from the past points to mechanisms in Earth’s early mantle that set off subduction, the geologic process in which one tectonic plate sinks beneath another in the mantle below, starting just 200 million years after Theia’s supposed impact—so soon that scientists have wondered how.
“In this study, we run whole-mantle convection models to illustrate that strong mantle jets can arise, weaken the lithosphere, and ultimately initiate subduction [about] 200 million years after the giant impact,” Yuan and colleagues explain in their published paper.
These jets, according to the team’s simulations, were created primarily by the temperature increase at the core-mantle boundary of the early Earth as a result of parts of Theia accreting there.
Another potential contributor is the spots themselves, which are iron-rich and dense. If they are indeed buried relics of Theia, as Yuan’s 2023 study suggests, then they likely resemble the geological content of Mars and contain more heat-producing elements than the surrounding mantle in which they sit.
Heat radiated from the spots may have given rise to strong jets that likely continued to trigger transient episodes of subduction as the core boundary cooled, the researchers found. This is consistent with earlier research suggesting that plate tectonics began with mantle uplift.
So Theia appears to have had a lasting impact, shaping Earth’s geological evolution from the inside out. According to Yuan and colleagues, their findings illustrate “the fundamental influence of the initial conditions determined by giant impact processes for the tectonic evolution of the terrestrial planets.”
But not all geologists agree. Some question how such a powerful collision could have stirred up Earth’s mantle without recycling all of the crust.
Previous research has also suggested that plate tectonics were formed by completely different processes: either the Earth heated and expanded to the point where its crust cracked, or, in another strange suggestion, our planet’s rocky surface was torn apart by gravitational forces.
Just as the theory of plate tectonics is still being refined, so will that of how these plates first formed.
The study was published in Geophysical Research Letters.
