North American Continent Isn't as Solid as You Might Think

The continent's ancient core actually is deformed. Continue reading →

You've heard the phrase "solid as a rock." But it turns out that at least as far as North America is concerned, the rock isn't necessarily so solid.

In a study published in Nature Geoscience, scientists from the GFZ German Research Centre for Geosciences reveal that North America's ancient rocky core actually is extremely deformed, and that its root actually shifts away from the center by nearly 530 miles to the west-southwest. Our continent in some ways resembles a person with scoliosis, a crooked spine.

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That shift in the root also runs counter to the previous assumption by scientists that the continents' rocky cores, called cratons, have been pretty much stable for the past 2.5 to 3.8 billion years, even as the continents themselves break up, drift apart and are pushed back together. The cratons are among the oldest geological features on the planet.

"We combined and analyzed several data sets from Earth's gravity field, topography, seismology and crustal structure and constructed a three dimensional density model of the composition of the lithosphere below North America," GFZ scientist Mikhail Kaban explained in a press release. "It became apparent that the lower part of the cratonic root was shifted by about 850 kilometers (528.17 miles)."

But you may be wondering how North America's craton got so messed up. The German scientists, who modeled the flow of the Earth's semi-molten mantle beneath the continent, say that the hot material flows westward at a velocity of about 4 millimeters - about 0.16 of an inch–per year. That may not seem like a lot, but it's enough to put the continental core out of kilter.

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"This indicates that the craton is not as solid and as insensitive to the mantle flow as was previously assumed," Kaban says.

The scientists believe this is evidence that there is far more mechanical, chemical and thermal interaction between the craton of billions of years in age and its surrounding in the upper mantle of Earth than previously believed.

A computer illustration shows fault lines between Earth's tectonic plates.

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