UMD Geologists Discover Ancient Sunken Seafloor From Dinosaur Era

Using seismic waves, University of Maryland scientists have discovered evidence of an ancient seafloor that sank hundreds of kilometers deep into the Earth during the age of dinosaurs, challenging existing theories about Earth’s interior structure.

Located in the East Pacific Rise (where two sections of the planet’s crust meet in the southeastern Pacific Ocean), this previously unstudied patch of seafloor sheds new light on the inner workings of our planet and how its surface has changed over millions of years. These findings were published Friday in the journal Science Advances.

The team led by geology Postdoctoral Associate Jingchuan Wang used innovative seismic imaging techniques to peer deep into Earth’s mantle, the layer between the Earth’s crust and core. The researchers found an unusually thick area in the mantle transition zone, a region located 410 to 660 kilometers below the Earth’s surface that separates the upper and lower mantles, expanding or contracting based on temperature. The newly discovered seafloor may also have caused an unusual split in a massive region in Earth’s lower mantle known as the Pacific Low Shear Velocity Province.

“This thickened area is like a fossilized fingerprint of an ancient piece of seafloor that subducted into the Earth approximately 250 million years ago,” Wang said. “It’s giving us a glimpse into Earth’s past that we’ve never had before.”

Subduction occurs when one tectonic plate slides beneath another, recycling surface material back into Earth's mantle. The process often causes earthquakes and leaves visible evidence of movement, including volcanoes and deep marine trenches. While geologists typically study subduction by examining rock samples and sediments found on Earth’s surface, Wang worked with geology Professor Vedran Lekic and Associate Professor Nicholas Schmerr to create detailed mappings of the structures hiding deep within the mantle with seismic waves.

“You can think of seismic imaging as something similar to a CT scan. It’s basically allowed us to have a cross-sectional view of our planet’s insides,” Wang said. “Usually, oceanic slabs of material are consumed by the Earth completely, leaving no discernible traces on the surface.”

What the team found was surprising: Material was moving through Earth’s interior much more slowly than previously thought. Wang believes that the unusual thickness of the area the team discovered suggests the presence of colder material in this part of the mantle transition zone, hinting that some oceanic slabs get stuck halfway down as they sink through the mantle.

“We found that in this region, the material was sinking at about half the speed we expected, which suggests that the mantle transition zone can act like a barrier and slow down the movement of material through the Earth,” Wang explained. “Our discovery opens up new questions about how the deep Earth influences what we see on the surface across vast distances and timescales.”

The team plans to extend its research into other areas of the Pacific Ocean and beyond. Wang hopes to create a more comprehensive map of ancient subduction and “upwelling” zones—where subducted material heats up and rises to the surface again—as well as their effects on both deep and surface Earth structures.

“We believe that there are many more ancient structures waiting to be discovered in Earth’s deep interior,” Wang said. “Each one has the potential to reveal many new insights about our planet’s complex past—and even lead to a better understanding of other planets beyond ours.”