250-Million-Year-Old Seafloor Found Deep in Earth’s Mantle

Buried hundreds of kilometers beneath our feet lies a startling discovery: an ancient seafloor, preserved for over 250 million years, hidden deep within Earth’s mantle. This extraordinary find was made by a research team using seismic imaging to peer into the planet’s enigmatic interior.

Led by Jingchuan Wang, a postdoctoral researcher in geology, the group employed innovative seismic imaging techniques to reveal a thickened area in the mantle transition zone, located between 410 and 660 kilometers beneath the surface. This discovery sheds light on the mysterious dynamics of Earth’s interior and may reshape our understanding of geological processes.

A "Fossilized Fingerprint" of Earth's History

Describing the findings, Wang called the thickened area “a fossilized fingerprint of an ancient piece of seafloor that subducted into the Earth approximately 250 million years ago.” Subduction—the process where one tectonic plate slides beneath another—recycles surface material into the mantle and often leaves visible evidence like volcanoes, earthquakes, and deep-sea trenches.

However, unlike typical surface-based studies, Wang’s team ventured into uncharted depths using seismic waves. Collaborating with Professors Vedran Lekic and Nicholas Schmerr, the researchers mapped the hidden structures of the mantle by analyzing how seismic waves traveled through different layers of Earth.

“You can think of seismic imaging as similar to a CT scan,” Wang explained. “It allowed us to get a cross-sectional view of our planet’s interior, unveiling structures we couldn’t observe otherwise.”

Anomalous Discovery in the Mantle

The team’s seismic “scan” revealed an unexpected finding: material in the mantle transition zone was moving much more slowly than previously thought. This sluggish movement suggests that colder, denser slabs of ancient oceanic crust may get “stuck” halfway down as they sink through the mantle.

“In this region, material was sinking at about half the speed we expected,” Wang said. “This suggests the mantle transition zone can act as a barrier, slowing the movement of material and preserving traces of Earth’s ancient geological processes.”

This preserved seafloor could also explain irregularities in the Pacific Large Low Shear Velocity Province (LLSVP), a massive structure in the lower mantle. The LLSVP appears to be split by the slab, hinting at a deeper relationship between ancient subduction events and current mantle dynamics.

Redefining Earth's Dynamic Histor

The implications of these findings are vast. Wang believes this ancient slab offers a missing link between deep Earth structures and surface geology. “This discovery opens up new questions about how the deep Earth influences what we see on the surface, spanning vast distances and timescales,” Wang said.

The team is already looking to expand their research beyond the Pacific Ocean, aiming to create a global map of ancient subduction zones and their impact on both deep and surface structures. Such maps could revolutionize our understanding of plate tectonics and Earth’s geological evolution.

Beyond Earth: A Cosmic Perspective

Wang sees this research as just the beginning. “We believe many more ancient structures are waiting to be discovered in Earth’s deep interior,” she said. Each new discovery could unravel further mysteries of our planet’s complex past and even provide insights into the geology of other planets.

By combining cutting-edge seismic techniques with deep curiosity, Wang and her team are not only rewriting the story of Earth’s interior but also laying the groundwork for understanding the dynamic processes shaping planetary bodies across the universe.

As Wang put it: “Each layer of discovery reveals more about our planet’s incredible history—and the mysteries that still lie beneath our feet.”