Scientists discovered remnants of a prehistoric seafloor beneath the Pacific Ocean

Deep beneath the Earth’s surface, researchers have uncovered striking new evidence of ancient seafloor buried for millions of years. This hidden remnant, detected using seismic waves, offers fresh insight into the planet’s shifting interior and its turbulent past. The discovery sheds light on geological processes that shaped Earth during the time of the dinosaurs.

Scientists used advanced imaging techniques to peer into an unexplored region of the mantle, a layer between the crust and the core. Their findings reveal a dense slab of oceanic crust that sank hundreds of kilometers underground, preserving a long-lost chapter of Earth's history.

Jingchuan Wang, a postdoctoral researcher in geology, led the study at the University of Maryland. His team focused on the East Pacific Rise, a geologically active region where segments of the planet’s crust slowly drift apart. Until now, this area had remained largely unexamined. Beneath its surface, researchers found a deep and unexpectedly thick structure unlike anything previously observed.

The team’s work, published in Science Advances, challenges long-standing ideas about Earth's mantle. Their findings suggest that ancient seafloor may persist far longer than scientists once believed, reshaping our understanding of plate tectonics. “This is a fossilized fingerprint of an ancient piece of seafloor that subducted into the Earth approximately 250 million years ago,” Wang explained.

To uncover these buried layers, researchers used seismic imaging, a technique that operates much like a CT scan. When earthquakes send shockwaves through the planet, the waves travel at different speeds depending on the material they pass through. By analyzing these patterns, scientists can map structures deep underground with remarkable precision.

Wang worked closely with geology professors Vedran Lekic and Nicholas Schmerr to apply this method to the mantle’s transition zone, a boundary located between 410 and 660 kilometers below the surface. This zone, where the upper and lower mantles meet, shifts in thickness based on temperature and pressure. The team’s findings revealed an unusually thick section, suggesting a complex history beneath the surface.

This buried seafloor challenges previous models of how Earth's interior evolves over time. Once thought to mix and dissolve relatively quickly, these ancient slabs may instead persist for hundreds of millions of years. Their survival could influence deep-earth processes in ways scientists are only beginning to understand.

Subduction is the process where one tectonic plate slides beneath another, pushing material from the Earth's surface deep into its mantle. This mechanism is crucial to understanding geological phenomena, as it often leads to earthquakes, volcanic activity, and the creation of deep ocean trenches.

Traditionally, subduction is studied by examining surface rock samples and sediment deposits, but this new approach offered a glimpse into the deeper consequences of this process. The team’s findings revealed that material in this section of Earth's interior was moving much more slowly than previously believed.

Wang noted that the presence of colder material in the mantle transition zone likely contributed to its unusual thickness, suggesting that oceanic slabs might become trapped midway as they descend into the mantle.

"We found that in this region, the material was sinking at about half the speed we expected," Wang explained. This surprising result indicates that the mantle transition zone might act as a barrier, slowing down the movement of subducted materials through Earth's layers.

This discovery, in turn, raises questions about how the dynamics of Earth's deep interior influence surface conditions across vast distances and timescales.

The impact of these findings goes beyond mere curiosity about Earth's geological history. The team hypothesizes that the unusual split in the Pacific Low Shear Velocity Province—an area deep within the mantle known for its complex geological behavior—may be linked to the sunken seafloor they discovered.

These insights help geologists better understand how Earth's interior layers interact, and how these interactions affect tectonic activities on the surface, such as earthquakes and volcanic eruptions.

The research team plans to expand its studies to include other regions of the Pacific Ocean and beyond. By examining more areas, they hope to create a comprehensive map of ancient subduction and “upwelling” zones. Upwelling occurs when subducted material heats up and rises toward the surface, contributing to volcanic activity.

A clearer picture of these zones could deepen the understanding of how deep mantle structures interact with the surface, potentially revealing connections between past geological events and the current behavior of Earth's crust.

“We believe that there are many more ancient structures waiting to be discovered in Earth’s deep interior,” Wang said. He emphasized that each of these hidden features has the potential to offer new insights into Earth's complex history.

Moreover, understanding these processes could also help in the study of other planets. “It’s giving us a glimpse into Earth’s past that we’ve never had before,” Wang added, highlighting the broader implications of their work.

This discovery emphasizes the dynamic nature of Earth's interior. While many think of the mantle as a uniform, slowly flowing layer of rock, it is much more intricate, with different materials moving at varying rates and even being recycled into new formations.

The East Pacific Rise's sunken seafloor stands as a reminder of the dynamic forces shaping the planet from the inside out—a slow but powerful dance of creation and destruction that has persisted for millions of years.

Understanding Earth’s deep mantle dynamics is crucial, not only for predicting geological events but also for gaining a complete picture of the planet’s history.

The work of Wang and his colleagues pushes the boundaries of current geological models, providing a more detailed and nuanced understanding of what lies beneath our feet. Their findings are a testament to how much more there is to learn about the Earth, even in regions that seem inaccessible.

In the coming years, as seismic imaging continues to improve, scientists hope to uncover more ancient secrets hidden beneath the Earth's surface.

These discoveries will not only help explain our planet’s past but could also inform how we understand and prepare for future geological changes—offering insights that extend beyond Earth to other planets in our solar system.

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