A big whack that made the moon may have also created continents that move

A big whack that made the moon may have also created continents that move

June 19, 2024 at 11:31 am
A rendering of Earth’s collision with a Mars-size planetary object 
called Theia 4.44 billion years ago. Computer simulations suggest that a 
collision with another planetary object early in Earth’s history may 
have provided the heat to set off plate tectonics. (Hernán Cañellas via 
The New York Times)

A rendering of Earth’s collision with a Mars-size planetary object 
called Theia 4.44 billion years ago. Computer simulations suggest that a 
collision with another... (Hernán Cañellas via The New York Times)More
By Lucas Joel
The New York Times
Some 4.5 billion years ago, many scientists say, Earth had a meetup with 
Theia, another planetary object the size of Mars. When the two worlds 
collided in a big whack, the thinking goes, debris shot into space, got 
locked into the orbit of the young, 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 given rise to something else: plate 
tectonics, the engine that drives the motion of Earth’s giant 
continental and oceanic plates and causes earthquakes, volcanic 
eruptions and the eventual remaking 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 offered. Qian Yuan, a 
postdoctoral researcher at the California Institute of Technology and an 
author of the new paper, and his colleagues make the case for the Theia 
collision as the source of plate tectonics. They reason from computer 
simulations that the event produced the heat needed in Earth’s early 
days to get the process going.

Tectonics starts with superheated plumes of magma from close to Earth’s 
core rising and sitting beneath the planet’s plates. The plumes can 
weaken the crust, and lava can erupt and push aside overriding plates.

Driven by the erupting lava, plates scrape past and collide with each 
other, and they can also dive beneath other plates and into the planet’s 
interior in a process called subduction.

In earlier research, Yuan described continent-size “blobs” floating some 
2,000 miles beneath Earth’s surface near the core. He and his team think 
those blobs are remnants of Theia that, delivered violently, created the 
heat needed to form the first tectonics-driving plumes. The giant blobs 
are believed to be connected to magma plumes, which means the blobs 
could be fueling plate tectonics.

“Simulations show the catastrophic, moon-forming giant impact ignited 
the engine that drives plate tectonics,” Yuan said.

Another clue is in Western Australia. There, in a place called the Jack 
Hills, rocks contain crystals that formed about 4.4 billion years ago — 
not long, geologically speaking, after Theia struck Earth.

Those crystals in Australia, called zircons, form only where there is 
plate subduction, and subduction can happen only on a planet with active 
plate tectonics.

Once Yuan learned that the zircons formed relatively soon after the 
Theia impact, he became convinced the collision had something to do with 
the start of plate tectonics.

Bradford Foley, a geophysicist at Pennsylvania State University, thinks 
that the idea of plate tectonics starting from a planetary collision has 
merit. But it is not the only way tectonics can start, he says.

“The giant impact is one possible way to make Earth’s core initially 
very hot,” he said. “It’s an interesting idea that I’m glad to see 
published for the scientific community to debate, but can easily be 
oversold and over-dramatized to the general public.”

An alternative explanation that the study does not refute, he says, is 
that the planetary core’s initial formation may have made it hot enough 
for tectonic activity to begin.

The challenge, Yuan explained, is in accurately representing the 
physical states of our planet from more than 4 billion years ago.

“We have confidence in our model, but does it really represent the whole 
true Earth?” Yuan said. “That’s a question to be explored by future tests.”

This story was originally published at nytimes.com. Read it here.
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