Picture this: deep beneath the American Midwest, the underside of Earth’s crust is slowly melting, forming molten blobs that drip into the p...
What’s Going On Down There?
Underneath North America lies a craton—a massive, stable chunk of Earth’s crust that’s been around for eons. Cratons are like the foundation stones of continents, and there are about 35 of them scattered across the globe. Normally, they’re tough and unchanging, but something funky is happening to the one under the Midwest.
Here’s the deal: when the bottom of this craton gets hot enough, the rock starts to melt. Over time, these molten drops grow heavy enough to break off and sink deeper into the mantle. Think of it like a super-slow-motion version of a pitch drop experiment—except instead of tar, it’s the stuff continents are made of. This process, dubbed lithospheric dripping, isn’t unique to North America—it’s been spotted in places like the Andes and Türkiye’s Anatolian Plateau, where it even wrinkles the surface. But under the Midwest, it’s more subtle, and we only found it thanks to some clever tech.
How Did We Figure This Out?
A team led by seismologist Junlin Hua (formerly at the University of Texas, now at the University of Science and Technology of China) used seismic data from the EarthScope Consortium to map what’s happening. They built a tomographic map—basically an X-ray of Earth’s crust—showing where it’s thick, thin, or changing density. “Because of this full-waveform method, we get a clearer picture of that key zone between the deep mantle and the lithosphere,” says geophysicist Thorsten Becker from UT Austin. And what they found? The North American craton is thinning out, with the Midwest as ground zero.
Why Is This Happening?
The plot thickens when you look at what’s driving this drip-fest. About 600 kilometers (373 miles) away, the ancient Farallon tectonic plate is sliding—or subducting—under the North American plate. This has been going on for hundreds of millions of years, and by now, most of the Farallon plate is chilling in the lower mantle. But its leftovers are stirring things up. Seismic data suggests it’s redirecting mantle flows that scrape along the craton’s underside, weakening it. Add in some volatile chemicals released from the sinking slab, and you’ve got a recipe for softened, drippy lithosphere.
Should We Be Worried?
Nope! This is geology on a glacial timescale—think millions to billions of years. It’s not like the Midwest is about to sink into the Earth anytime soon. In fact, this process is widespread across the craton, not just under Kansas cornfields. It’s a slow, natural part of how planets evolve. As Becker puts it, “This sort of thing is important if we want to understand how a planet has evolved over a long time. It helps us figure out how continents form, break apart, and get recycled.”
Why It Matters
This discovery isn’t just cool trivia—it’s a window into Earth’s past and future. Cratons are the building blocks of continents, and understanding how they thin or shift could unlock secrets about how North America came to be. Plus, it’s a reminder that our planet is anything but static. Even the “stable” bits are quietly reshaping themselves, one molten drip at a time.
The research, published in Nature Geoscience, is a testament to how cutting-edge tools like seismic imaging can reveal hidden stories beneath our feet. So next time you’re driving through the Midwest, just imagine: under all that flatland, Earth’s crust is putting on a slow-motion show, dripping away into the abyss.
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