Geologists uncover ancient seafloor, transforming understanding of Earth’s interior

SciTechDaily discloses that geologists have made a groundbreaking discovery beneath the Pacific Ocean, revealing a mysterious subduction zone that challenges existing theories about the Earth's interior.

A team from the University of Maryland has utilized advanced seismic techniques to reveal remnants of an ancient seafloor, providing new insights into the deep structures of our planet. This discovery indicates that the movement of subducted materials occurs more slowly than previously thought, challenging existing theories about Earth's internal dynamics.

Scientists from the University of Maryland have located remnants of a prehistoric seafloor that descended into the Earth's depths during the age of dinosaurs, raising questions about established concepts of the Earth's interior structure. Found at the East Pacific Rise, a tectonic boundary on the seabed of the southeastern Pacific Ocean, this unexplored section of seafloor unveils new details about the planet’s inner processes and its extensive history over millions of years. The team's findings were published on September 27, 2024, in the journal Science Advances.

Led by geology postdoctoral researcher Jingchuan Wang, the team employed innovative seismic imaging techniques to investigate the Earth's mantle, the layer situated between the crust and the core. They identified an unusually thick area within the mantle transition zone, located approximately 410 to 660 kilometers below the Earth's surface. This zone, which separates the upper and lower mantles, expands or contracts with temperature variations.

The researchers propose that the newly discovered seafloor could also help explain the unusual structure of the Pacific Large Low Shear Velocity Province (LLSVP)—a vast area within the Earth's lower mantle that appears to be divided by the subducted slab. “This thickened area resembles a fossilized fingerprint of an ancient seafloor that sank into the Earth around 250 million years ago,” Wang stated. “It provides us with an unprecedented glimpse into the Earth’s history.” 

Subduction occurs when one tectonic plate moves beneath another, recycling surface material back into the mantle. This process often leaves visible signs of movement, such as volcanoes, earthquakes, and deep marine trenches. While geologists usually study subduction through rock samples and sediments at the surface, Wang collaborated with Geology Professor Vedran Lekic and Associate Professor Nicholas Schmerr to utilize seismic waves to explore beneath the ocean floor. By analyzing the travel patterns of these waves through various layers of the Earth, the scientists were able to create detailed maps of the structures hidden deep within the mantle. 

“Think of seismic imaging as akin to a CT scan. It essentially provides a cross-sectional view of our planet’s interior,” Wang explained. “Typically, oceanic slabs are entirely consumed by the Earth, leaving no discernible traces on the surface. However, observing the ancient subduction slab from this perspective has granted us new insights into the relationship between deep Earth structures and surface geology, which were previously unclear.” What the team discovered was surprising: materials within the Earth’s interior were moving at a much slower rate than anticipated. 

Wang suggests that the unusual thickness of the identified area indicates the presence of cooler materials in this mantle transition zone, implying that some oceanic slabs may become lodged halfway down as they descend. “We found that in this region, material was sinking at about half the expected speed, which suggests that the mantle transition zone can act as a barrier, slowing down material movement through the Earth,” Wang noted. 

“Our findings raise new questions about how deep Earth dynamics influence surface phenomena across vast distances and timescales.” Looking forward, the team aims to broaden their research to other areas of the Pacific Ocean and beyond. Wang hopes to develop a more comprehensive map of ancient subduction and upwelling zones—geological processes where subducted material heats and rises back to the surface—and their effects on both deep and surface structures of the Earth. 

Utilizing the seismic data gathered from this study, Wang and his colleagues are refining their models of tectonic plate movements throughout Earth’s history. “This is just the beginning,” Wang stated. “We believe there are many more ancient structures yet to be discovered within the Earth’s depths. Each of these has the potential to unveil new insights about our planet’s complex past—and may even enhance our understanding of other planets beyond our own.”

By Naila Huseynova