When a giant body plunged into the primordial Earth 4.5 billion years ago, the impact determined the planet’s future and formed the moon.
The object, now called Theia, was about the size of Mars. It more or less fragmented on impact. Most of it eventually coalesced several hundred thousand kilometers away and became the moon. The remnants, the theory goes, sprayed off into deep space.
One Caltech research team doesn’t think so. Hongping Deng of the Shanghai Astronomical Observatory (SHAO) of the Chinese Academy of Sciences led a study that suggests substantial pieces of Theia are lodged deep in the Earth’s mantle.
If true, it would alter the course of evolutionary geology.
Deng explained to Sciencealert that chunks of Theia sank into the Earth’s surface but then became “homogenized” inside its molten inner structure.
“Instead, the Moon-forming giant impact appears to be the origin of the early mantle’s heterogeneity,” Deng said. “[It] marks the starting point for the Earth’s geological evolution over the course of 4.5 billion years.”
Our (partly) alien world
Put differently, Deng and company think our planet’s evolution is in part extraterrestrial.
The pieces of this bygone cosmic wrecking ball now exist as structures deep below Earth’s surface. They’re called large low-shear-velocity provinces, or LLVPs. They lie sandwiched between planetary layers far below the surface, possibly surfing on an ocean of magma. One lies roughly below Africa, the other below the Pacific Ocean.
The researchers used computer simulations to show that the two LLVPs are 2.0-3.5% denser than surrounding materials, sci.news reported. That discrepancy suggests they could have originated in Theia.
“It appears that Earth’s blobs are remnants of a planetary collision that formed our Moon,” said Arizona State University’s Ed Garnero.
“In other words, the massive blobs currently inside Earth, deep beneath our feet, are extraterrestrial. Earth not only has ‘blobs,’ Earth has extraterrestrial blobs!”
Their deposition was a tumultuous time for the Blue Planet. If the Caltech team is on target, Earth not only became extraterrestrial in an instant — it also could have received its moon in about an hour.
