Two giant blobs are lurking deep within the Earth, but why?

Scientists have long been baffled by Earth’s violent forces, such as earthquakes and volcanoes. Their origins are explained by a recent study that suggests the cause was a cosmic collision billions of years ago.

Who’s at fault? Researchers have identified two massive, peculiar blobs deep within Earth that they have named Large Low-Velocity Provinces (LLVPs). The secret to plate tectonics, the process that drives Earth’s geology, may lie in these enigmatic masses, which were created from the debris of a planet-sized impact.

The Improbable Past

Imagine a massive collision between Earth and a planet the size of Mars. The moon was probably formed by this apocalyptic event, which is thought to have happened 4.5 billion years ago, and left behind the LLVPs. The majority of scientists think that over time, the impact debris homogenized inside the Earth’s mantle. Nevertheless, a 2023 study suggested that the LLVPs are the remains of Theia, the planet that collided.
Astrophysicist Steven Desch of Arizona State University, who co-authored the Nature study, said, “The moon appears to contain materials within it representative of both the pre-impact Earth and Theia, but it was thought that any remnants of Theia in the Earth would have been ‘erased’ and homogenized by billions of years of dynamics (e.g., mantle convection) within the Earth.” This study is the first to demonstrate that unique “pieces” of Theia are still present at the Earth’s core-mantle boundary.

A Twist in the Mantle

Building on this theory, a new computer model indicates that about 200 million years after the impact, these hot, dense blobs stirred the interior of Earth. The planet’s surface may have been disturbed by hot plumes that formed as a result of this churning. Subduction is the process by which rock slabs sank back down as a result of these plumes rupturing the crust.

The discovery of ancient zircon crystals, which provide proof of subduction more than 4 billion years ago, is consistent with this model. According to Qian Yuan, co-author of the study, the massive impact not only created the moon but also paved the way for plate tectonics, an essential process for life.

Open Questions and Shifting Theories

Another study adds a wrench to the argument, raising questions about whether the collision initiated plate tectonics or merely recycled Earth’s crust. According to this theory, life first emerged some 3.9 billion years ago, possibly during a period when plate tectonics was dormant.

“We discovered that plate tectonics did not exist when life is first thought to have originated and that it did not exist for hundreds of millions of years afterward. According to University of Rochester paleogeologist John Tarduno, “Our data suggests that when we’re looking for exoplanets that harbor life, the planets do not necessarily need to have plate tectonics.”

The Enduring Mystery

The question of how plate tectonics contributed to the emergence of life is still up for debate. Some argue that it was not present when life first emerged, while others maintain that it is necessary for the carbon cycle that keeps life alive. Science is still investigating the how, when, and why of life’s origin on our dynamic planet, as well as the part these shifting plates played.