A recent study has uncovered a remarkable geological process occurring deep beneath the Midwestern United States: a buried remnant of an ancient tectonic plate, known as the Farallon slab, is pulling the underside of the North American crust down into the mantle. This phenomenon is resulting in what scientists describe as “drips” of rock that extend up to 400 miles (640 kilometers) deep into the Earth. These mantle drips, spread beneath a region from Michigan to Nebraska and Alabama, suggest a large-scale reconfiguration of the continent’s subsurface.
The researchers found that this slab is creating a funnel-like structure underground, drawing in rocks horizontally from across North America before dragging them downward. This subsurface motion is causing significant loss of material from the base of the continental crust. According to lead author Junlin Hua, this thinning process affects a wide portion of the continent.
At the heart of the study is a process called cratonic thinning—the gradual erosion of cratons, which are ancient, stable parts of the Earth’s lithosphere. Cratons have remained largely unchanged for billions of years, but this study offers the first direct evidence of their transformation in real time. The Farallon slab, a remnant of a tectonic plate that once subducted beneath North America, is thought to be the driving force behind this thinning. Though the slab began its descent roughly 20 million years ago, its current position—about 410 miles (660 km) deep—continues to exert a strong influence.
Using a cutting-edge seismic imaging technique called full-waveform inversion, Hua and his team were able to visualize this deep-Earth phenomenon with unprecedented clarity. This method analyzes how various seismic waves travel through the planet’s interior, revealing detailed structural information. The resulting images show the dripping mantle features and how they align with the predicted location of the Farallon slab.
To confirm their hypothesis, the researchers ran simulations comparing scenarios with and without the presence of the slab. The dripping structures only formed when the slab was included, reinforcing the idea that the Farallon remnant is responsible for the subsurface flow and associated cratonic thinning.
Despite the dramatic processes occurring deep below, researchers note that these changes are unlikely to affect surface conditions anytime soon. As the slab sinks further into the lower mantle, its influence may gradually diminish. Still, this study offers crucial insights into the long-term evolution of continents. According to co-author Thorsten Becker, understanding these processes helps geologists piece together how continents are formed, reshaped, and recycled over geological timescales.
Ultimately, this research highlights the dynamic nature of Earth’s interior and provides the first real-time evidence of cratonic thinning in action. It challenges long-held assumptions about the permanence of cratons and underscores the powerful role ancient tectonic remnants continue to play in shaping the planet’s structure. The ongoing study of this phenomenon may reshape how scientists understand Earth’s internal processes and the life cycles of continents. The documentation of cratonic thinning not only advances geophysical science but also opens new questions about the stability and future of continental interiors.