'Giant Impact' May Have Set Off Plate Tectonics

The plate tectonics that determine the shape of our continents may have originated from a huge impact billions of years ago.

This huge collision with the Earth, thought to have occurred around 4.5 billion years ago, may have created huge "blobs" of material near our planet's core, according to a new study in the journal Geophysical Research Letters.

These blobs are thought to have shaped how the tectonic plates moved over time and, therefore, are responsible for our continents' current location.

Plate tectonics is the theory that explains the structure and motion of Earth's outermost layer—the lithosphere—which is divided into several large and several smaller plates, like the cracked shell of an egg. These plates are thought to have been slowly moving for billions of years, shifting the shapes of Earth's landmasses over time from the supercontinent of Pangaea.

Between these tectonic plates are boundaries, which move over and under each other via subduction, apart from each other—often occurring at the mid-ocean ridges where magma rises from beneath the Earth's surface to fill the gap—or horizontally past each other, like at the along the San Andreas Fault in California. The movement of tectonic plates is driven by several forces, including convection currents in the Earth's mantle due to heat from the Earth's core.

According to the paper, these plates may have begun their movement due to strange blobs, known as large, low-velocity provinces (LLVPs), that formed in the wake of a huge collision that also formed the moon around 4.5 million years ago.

"Plate tectonics remains unique to Earth, but when and how it started is debated. Earth's oldest minerals indicate a clement surface by 4.3 Ga, resembling the modern Earth with its granitic crust and oceans. Granite is most easily explained as originating from subduction. However, the mechanisms for subduction initiation, especially so soon after the Moon-forming giant impact, remain elusive," the researchers wrote in the paper.

These LLVPs are thought to be the remnants of the huge object Theia that collided with the Earth, sending so much debris into space that they coalesced to form our moon. Evidence of the existence of LLVPs was first found in the 1980s, below the Pacific Ocean and Africa.

The researchers modeled the LLVPs and simulated how they may have impacted the Earth's crust in the billions of years since. They found that around 200 million years after the collision, pressure from the LLVPs created hot plumes in the mantle that caused certain areas of the surface to sink, leading to subduction. This, therefore, created the cracks in the crust that kick-started the modern process of plate tectonics.

"The mantle thermochemical structure left by the Moon-forming impact triggers strong plumes that may have initiated the first subduction. "The strong mantle plumes may rise from a heated core or from large low-shear velocity provinces enriched in heat-producing elements," the researchers wrote.

"Early giant impact events may have a profound influence on the diverse tectonic regimes of rocky planets."

Do you have a tip on a science story that Newsweek should be covering? Do you have a question about plate tectonics? Let us know via science@newsweek.com.