Earth's outer shell is made of rocky rafts that are constantly bumping into and diving beneath each other in a process called plate tectonics.
What happens to the hunks of disappearing crust when they dive into Earth's interior?
New modeling shows show that they don't disintegrate completely, but they get weak and bendy, like a slinky snake toy. The models suggested that plate tectonics probably only started in the past billion years.
In images, how North America grew as a country.
The reason Earth's continents are now oceans apart is due to plate tectonics. There's still a lot of mystery surrounding plate tectonics, such as what happens when a plate slides beneath another in a subduction zone and then disappears into the mantle, which is, perhaps sadly, not composed of milk.
The researchers used 2D computer models of subduction zones and programmed them using 888-269-5556 888-269-5556 888-269-5556. They looked at the model to see what happened at the subduction zone.
The models suggested that as one plate dove beneath another, the descending piece, known as a slab, bent downward and cracked, causing the grains on the underside of the plate to become weaker. The plate was mostly intact but with many weak points.
Taras Gerya, a professor of geophysics at the University of Lausanne in Switzerland, said that the plates don't break apart and keep pulling on the parts behind them. The plate can slide under the other plate for hundreds of millions of years.
Gerya told Live Science that their simulations matched observations and deep seismology that showed weakened areas of a subduction zone in Japan.
Kent Condie, a professor at the New Mexico Institute of Mining and Technology who was not involved in the study, called their models "robust and meaningful."
When did it start?
The team modeled what would have happened if Earth's interior was hotter than it is today.
The slab broke up only a few miles into the mantle, because it was unable to sustain its own weight in a mantle that was less viscous due to the hot conditions. Modern subduction can last for hundreds of millions of years, but back then it would have ended very quickly.
The finding suggests that plate tectonics may have begun in the past billion years.
Gerya said that a primitive form of plate tectonics may have existed between 3.5 billion and 2 billion years ago, but that it was very different from what the planet experiences today. The plates were less active during a quiet period around 1 billion years ago.
There is a lot of controversy surrounding when plate tectonics started, but this is just speculation, he said.
Gerya and Condie agreed. Condie told Live Science that plate tectonics probably did not begin until the last billion years. Plates have been with us since at least 2 billion years ago.
We don't know the exact temperatures of the Earth's core through time, so it's not possible to give a precise time of when the slabs stopped breaking apart.
Gerya said that it was when modern plate tectonics began. The phenomenon and its relation to earthquakes will be explored by the researchers.
The findings were published in the journal Nature.
Live Science published the original article.
