Discovery of Mysterious Ancient Sunken Seafloor Could Rewrite Earth’s History

Geologists discovered a mysterious subduction zone deep beneath the Pacific Ocean, reshaping our understanding of Earth’s interior.

A team from the University of Maryland has discovered remnants of an ancient seafloor using new seismic techniques, offering fresh insights into Earth’s deep structures. This find suggests slower-than-expected movement of subducted material, impacting theories of Earth’s interior dynamics.

Discovery of Ancient Seafloor

Scientists from the University of Maryland have identified remnants of a prehistoric seafloor that plunged into the Earth’s depths during the age of dinosaurs, calling into question prevailing views on the Earth’s interior structure. Found at the East Pacific Rise, a tectonic boundary on the floor of the southeastern Pacific Ocean, this previously unexplored segment of seafloor reveals new aspects of our planet’s inner processes and its transformative history over millions of years. The team’s findings were published on September 27, 2024, in the journal Science Advances.

Seismic Imaging Breakthroughs

Led by geology postdoctoral researcher Jingchuan Wang, the team used innovative seismic imaging techniques to peer deep into Earth’s mantle, the layer between our planet’s crust and core. They found an unusually thick area in the mantle transition zone, a region located between about 410 and 660 kilometers below the Earth’s surface.

The zone separates the upper and lower mantles, expanding or contracting based on temperature. The team believes that the newly discovered seafloor may also explain the anomalous structure of the Pacific Large Low Shear Velocity Province (LLSVP)—a massive region in Earth’s lower mantle—as the LLSVP appears to be split by the slab.

Insights From Subducted Seafloor

“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 leaves visible evidence of movement, including volcanoes, earthquakes, 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 use seismic waves to probe through the ocean floor. By examining how seismic waves traveled through different layers of Earth, the scientists were able to create detailed mappings of the structures hiding deep within the mantle.

“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. But seeing the ancient subduction slab through this perspective gave us new insights into the relationship between very deep Earth structures and surface geology, which were not obvious before.”

The Slow Movement of Subducted Material

What the team found surprised them—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.”

Future Research Directions

Looking ahead, the team plans to extend their research into other areas of the Pacific Ocean and beyond. Wang hopes to create a more comprehensive map of ancient subduction and upwelling (the geological process that occurs when subducted material heats up and rises to the surface again) zones, as well as their effects on both deep and surface Earth structures. With the seismic data acquired from this research, Wang and other scientists are improving their models of how tectonic plates have moved throughout Earth’s history.

“This is just the beginning,” Wang said. “We believe that there are many more ancient structures waiting to be discovered in Earth’s deep interior. 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.”

Reference: “Mesozoic intraoceanic subduction shaped the lower mantle beneath the East Pacific Rise” by Jingchuan Wang, Vedran Lekić, Nicholas C. Schmerr, Yu J. Gu, Yi Guo and Rongzhi Lin, 27 September 2024, Science Advances.
DOI: 10.1126/sciadv.ado1219

This research was supported by NASA SSERVI Cooperative Agreement No. 80NSSC19M0216. This article does not necessarily reflect the views of this organization.