Scientists at the University of Texas at Austin have found something unexpected—deep underground, parts of the rock beneath North America are slowly breaking off and sinking deeper into the Earth. This process is called “cratonic thinning.” It is happening because an old tectonic plate, which has been slowly moving downward for millions of years, is affecting the deep layers of the continent. As a result, the underground structure of North America is changing over time.
What is happening under North America?
Scientists have discovered that deep underground, some rock pieces beneath North America are breaking off and slowly sinking further into the Earth. This is happening because of the Farallon Plate, an old tectonic plate that has been moving downward for millions of years.
A study published in Nature Geoscience confirms that this process is currently happening in the Midwest region of the United States. Even though it occurs far below the surface, it is affecting a large part of North America, including areas in both the US and Canada.
What are cratons, and why is this important?
Cratons are very old and stable parts of the Earth’s crust that have existed for billions of years. Normally, they remain unchanged for a long time. But sometimes, the deep layers of cratons break off or weaken, making the crust thinner. This process has happened before, such as in the North China Craton.
By observing cratonic thinning in real time, scientists can learn more about how continents evolve over millions of years.
How is the Farallon Plate causing this?
The Farallon Plate was first discovered in the 1990s. Scientists believe it is changing the flow of hot rock in the mantle and releasing chemicals that weaken the craton’s deep layers. This makes parts of the craton “drip away” into the mantle.
Computer models confirm this idea—when scientists remove the Farallon Plate from their simulations, the dripping effect stops.
This process is very slow and does not pose any immediate risk to the land or people living above. However, it is important for scientists because it helps explain how continents form, break apart, and recycle into the Earth over time.
Researchers used a new full-waveform seismic tomographic model based on data from the EarthScope project. This method allowed them to see the interactions between the crust and mantle in great detail.
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