Ancient seafloor re-emerges, giving us a new look at Earth's past

In a thrilling revelation that challenges existing theories about the structure of Earth’s interior, scientists have uncovered evidence of an ancient seafloor that sank deep into the Earth during the age of dinosaurs.

This previously unstudied tract of seafloor, located in the East Pacific Rise, has opened a window into how the planet’s surface has evolved over millions of years.

Ancient seafloor in Earth’s mantle

Led by researchers from the University of Maryland, the study changes our understanding of Earth’s mantle transition zone, located between the upper and lower mantles.

At the helm of this research was postdoctoral researcher Jingchuan Wang, who led the team using advanced seismic imaging technologies.

By peering into the mantle – 410 to 660 kilometers below Earth’s surface – the researchers discovered a peculiarly thick zone.

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

The discovery challenges existing models of tectonic plate movement and mantle dynamics.

Geological time machine

Subduction, where one tectonic plate slides beneath another, often leaves traces in the form of volcanoes, earthquakes, and marine trenches.

Typically, researchers study subduction by examining rock samples, but Wang and his colleagues took a different approach.

Working with Professor Vedran Lekic and Professor Nicholas Schmerr, Wang used seismic waves to analyze the structure of the ocean floor.

“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,” said Wang.

“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.”

Earth’s mantle influences the surface

The team’s findings suggest that material in the mantle moves much slower than previously thought.

Wang believes the unusual thickness in the mantle transition zone is caused by colder material, indicating that some oceanic slabs may be getting stuck mid-way as they descend.

This discovery challenges the assumption that subducted material always moves smoothly through the mantle, raising new questions about how these stalled slabs affect long-term tectonic activity, volcanic hotspots, and even the planet’s magnetic field.

“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.”

Climate and mantle dynamics

The research may also reshape our understanding of the mantle’s thermal and compositional structure.

The subduction of ancient seafloor slabs plays a critical role in Earth’s carbon cycle and mantle dynamics.

As these slabs descend, they transport surface materials, including carbon, deep into the mantle, influencing long-term carbon storage and release through volcanic activity.

This process also affects mantle convection, with thicker slabs slowing down heat transfer and altering tectonic and volcanic behavior.

The discovery of these ancient slabs reshapes our understanding of how Earth’s interior processes impact surface climate and geodynamics over time.

Future research directions

Looking ahead, the team plans to expand their research across the Pacific Ocean and beyond, mapping ancient subduction zones and their impact on Earth’s surface and deep structures.

The researchers aim to gather more seismic data to create a detailed global map of these hidden formations, helping scientists better understand how tectonic movements have shaped the planet over millions of years.

The research could also have practical applications for geohazard prediction, improving early warning systems for earthquakes and volcanic activity in high-risk areas.

Insights about Earth and other planets

In addition, the methods and insights developed in this study could be applied to the exploration of other planets.

Similar geological processes may be at work beneath the surfaces of Mars and Venus, offering clues to their histories and internal structures.

“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.”

The study is published in the journal Science Advances.

—–

Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates. 

Check us out on EarthSnap, a free app brought to you by Eric Ralls and Earth.com.

—–