Many scientists say that about 4.5 billion years ago, Earth met Theia, another Mars-sized planetary body. When the two worlds collided in a big blow, so the thinking goes, the debris was launched into space, got trapped in the orbit of the young Earth, damaged Earth and led to the formation of our Moon.
But the collision with Theia may have done more than that, according to a study published last month in the journal Geophysical Research Letters. The impact may have triggered something else: plate tectonics, the engine that drives the movement of Earth’s giant continental and oceanic plates and causes earthquakes, volcanic eruptions and ultimately reshaping of our planet’s surface about every 200 million years.
Earth scientists have long studied and debated the origin of plate tectonics, and other theories have been advanced. Qian Yuan, a postdoctoral researcher at Caltech and author of the new paper, and his colleagues make the case for a Theia collision as a source of plate tectonics. They concluded from computer simulations that the event produced the heat necessary in Earth’s early days to start the process.
Tectonics begins with super-hot plumes of magma approaching the Earth’s core, rising and settling beneath the planet’s plates. Plumes can weaken the Earth’s crust, and lava can erupt and push major plates aside.
Under the influence of exploding lava, plates collide with each other, and can also dive under other plates and into the planet’s interior in a process called subduction.
In previous research, Dr. Yuan described continent-sized “blobs” floating about 1,200 miles below the Earth’s surface near the core. He and his team believe those blobs are remnants of Theia, which, when violently released, created the heat needed to form the first plumes that drove tectonics. The giant blobs are thought to be linked to magma plumes, meaning the blobs could fuel plate tectonics.
“Simulations show that the catastrophic giant impact that led to the formation of the Moon ignited the engine that drives tectonic plates,” Dr. Yuan said.
Other evidence is found in Western Australia. There, in a place called Jack HillsThe rocks contain crystals that formed about 4.4 billion years ago, geologically speaking, not long after Theia collided with Earth.
Those crystals found in Australia, called zircons, only form when there is plate subduction, and subduction can only happen on a planet with active plate tectonics.
Once Dr. Yuan learned that zircons formed relatively soon after Theia’s collision, he became convinced that the collision had something to do with the beginning of plate tectonics.
Bradford Foley, a geophysicist at Pennsylvania State University, thinks the idea of plate tectonics starting from planetary collisions has merit. But he says this is not the only way tectonics can start.
“A giant impact is one possible way to make the Earth’s core very hot to begin with,” he said. “It’s an interesting idea, and I’m happy to see it published for the scientific community to discuss, but it could easily be over-hyped and blown out of proportion to the general public.”
An alternative explanation that the study does not refute is that the initial formation of the planetary core may have made it hot enough to initiate tectonic activity, he says.
Dr. Yuan explained that the challenge lies in accurately representing the physical conditions of our planet more than four billion years ago.
“We have confidence in our model, but does it really represent the entire real Earth?” Dr. Yuan said. “This is a question that should be explored through future testing.”
