Deep beneath Earth’s surface, researchers have discovered an ancient seafloor buried for millions of years. This unexpected find, detected through seismic waves, offers new insight into Earth’s shifting interior and the turbulent geological processes that have shaped the planet since the time of the dinosaurs.
A Prehistoric Ocean Floor Hidden Deep Within the Mantle
The study, led by Jingchuan Wang, a postdoctoral researcher at the University of Maryland, reveals that a dense slab of oceanic crust sank hundreds of kilometers underground, preserving a long-lost chapter of Earth’s history.
Using seismic imaging, Wang and his team studied the East Pacific Rise, a geologically active region where Earth’s crust slowly drifts apart. Despite its significance, this area had remained largely unexplored—until now. Beneath its surface, scientists found an unexpectedly thick and dense structure, unlike anything previously observed in Earth’s mantle.
Seismic waves, which travel at different speeds depending on the material they pass through, helped researchers map these hidden underground structures. Their findings suggest that a massive portion of an ancient seafloor subducted into the Earth about 250 million years ago and has remained intact ever since.
Challenging Long-Held Ideas About Earth’s Mantle
The discovery, published in Science Advances, challenges traditional views of how Earth’s interior evolves over time. Scientists have long believed that subducted oceanic crust mixes and dissolves relatively quickly within the mantle. However, this research suggests that ancient slabs may persist for hundreds of millions of years, fundamentally altering our understanding of plate tectonics.
The team applied seismic imaging techniques similar to a CT scan, analyzing how earthquake shockwaves travel through the planet’s interior. These methods allowed them to map deep structures with remarkable precision, revealing an unusually thick section in the mantle transition zone, located between 410 and 660 kilometers below the surface.
This zone serves as the boundary between Earth’s upper and lower mantle. Its thickness varies based on temperature, pressure, and the presence of different materials. The discovery of an unexpectedly dense layer suggests that subducted slabs might become trapped instead of fully descending into the lower mantle, contradicting previous geological models.
A Slow-Moving Relic of Earth’s Past
One of the study’s most surprising findings is that the material in this buried seafloor is moving significantly slower than expected. The presence of colder, denser material in the mantle transition zone appears to act as a barrier, slowing down the sinking process of subducted oceanic slabs.
“We found that in this region, the material was sinking at about half the speed we expected,” Wang explained.
This suggests that subducted slabs don’t just disappear into the mantle but instead linger for extended periods, influencing Earth’s deep structure in ways scientists are only beginning to understand.
Why Does This Discovery Matter?
Understanding how subduction affects Earth’s deep interior is essential for studying earthquakes, volcanic activity, and the formation of deep-sea trenches. Subduction—the process where one tectonic plate slides beneath another—has long been studied through surface rock samples and sediment deposits.
However, this new approach provides a rare glimpse into the deeper consequences of this process, revealing how Earth’s mantle might behave on much longer timescales. The research also raises new questions about how deep-Earth dynamics influence surface conditions across vast distances and timescales.
One intriguing possibility is that the unusual split in the Pacific Low Shear Velocity Province—a deep mantle region known for its complex geological behavior—may be linked to the sunken seafloor detected by the team.
Mapping Earth’s Ancient Past—One Lost Seafloor at a Time
This research is just the beginning. Wang and his colleagues plan to expand their studies to other regions of the Pacific Ocean and beyond. By identifying more ancient subduction zones, they hope to create a global map of buried oceanic slabs.
Their work also highlights the connection between deep mantle structures and surface geological activity. When subducted material heats up and rises back toward the surface, it can lead to volcanic activity, a process known as mantle upwelling.
A clearer understanding of subduction, mantle transition zones, and LLSVP (Large Low Shear Velocity Province) distributions could provide critical insights into how Earth’s crust behaves over millions of years.
What Does This Mean for Earth’s Future?
This discovery reshapes our understanding of Earth’s mantle dynamics and suggests that many more ancient structures could be hidden deep within the planet.
“We believe that there are many more ancient structures waiting to be discovered in Earth’s deep interior,” Wang stated.
Each of these hidden features could offer new insights into our planet’s geological evolution, potentially unlocking secrets about Earth’s past and even other planetary bodies.
This research challenges the notion that Earth’s mantle is a uniform, slowly flowing layer of rock. Instead, it reveals a far more intricate and dynamic interior, where different materials move at varying speeds and are recycled into new formations over millions of years.
The East Pacific Rise’s sunken seafloor is a striking example of the forces shaping Earth from the inside out—a continuous cycle of creation and destruction that has been unfolding for hundreds of millions of years.
