Like a giant broken cookie whose pieces float on top of a sea of boiling milk, Earth’s outer shell is made up of rocky (less tasty) rafts that constantly collide and dive under each other in a process. called plate tectonics.
So what happens to these pieces of crust that disappear as they dive into the milky interior of the Earth?
Turns out they weaken and bend, like a slinky snake toy, but don’t completely disintegrate, New Modeling Shows. Models also suggest that plate tectonics, at least in its modern form, probably only started in past billion years.
Plate tectonics cause earthquakes & volcanoes, create mountain ranges and islands, and is why the continents of Earth, once a supercontinent, are now separate oceans. But how plate tectonics work is still very much unknown, such as what happens when one plate slides under another (in an area called a subduction zone) and disappears into the mantle, the planet’s middle layer, which, perhaps unfortunately, is not made of milk but rather of solid, sparkling rock.
To understand this, the researchers used 2D computer models of subduction zones and programmed them using known physics of material behavior, such as how rocks deform under certain forces. Then they looked at the model to see what happened in the subduction zone and compared their results to actual observations.
Their models suggested that when one plate dove under another, the descending piece, known as the slab, would suddenly bend downward and crack; the folding also made the grains on the underside of the plate thinner and weaker. The pressures left the plate almost intact but with many weak points.
This means that the plates don’t break and keep pulling the pieces behind them, “for a long time,” said lead author Taras Gerya, professor of geophysics at ETH Zurich in Switzerland. In fact, the plate can continue to slide under the other plate for hundreds of millions of years, he said.
Their simulations matched observations and deep seismic imagery that showed weakened areas of a subduction zone in Japan, Gerya told.
Kent Condie, professor emeritus of geochemistry and earth and environmental sciences at the New Mexico Institute of Mining and Technology who was not involved in the study, called their models “robust. and significant “.
When did it start?
The team also modeled what would have happened if the Earth’s interior had been warmer than 270 degrees Fahrenheit (150 degrees Celsius), similar to temperatures it would have reached about a billion years ago.
They found that in these simulations, the slab only broke a few miles in the mantle, as it was unable to support its own weight in a less viscous mantle due to the warm conditions. So unlike modern subduction which can go on for hundreds of millions of years, subduction would have ended very quickly, within a few million years, Gerya said.
This discovery suggests that modern plate tectonics may not have started until the last billion years, he added.
While a primitive form of plate tectonics may have existed between 3.5 and 2 billion years ago, during the Archean or Proterozoic eras, it was probably very different from what the planet experience today, said Gerya. And about 1.8 billion to 1 billion years ago, there was a quiet period when the plates were much less active.
But this is only speculation, he said, and there is currently a lot of controversy over the onset of plate tectonics.
Condie agreed with Gerya. “Modern plate tectonics, with all the geological markers … it probably didn’t start until the last billion years,” Condie told . But “plate tectonics, in some form, has been around for at least 2 billion years.
However, as we do not know the exact temperatures of the Earth’s core over time, it is not yet possible to provide an accurate timeline of when the slabs stopped breaking and began a more continuous journey through the mantle. , said Condie.
This is when modern plate tectonics began, Gerya said. Researchers now hope to explore the phenomenon and its relationship to earthquakes using more advanced 3D models.
The findings were published in the journal Nature.