Researchers have uncovered evidence of long-lost seafloor below the Pacific Ocean, which could rewrite Earth’s history.
They discovered remnants of an ancient seafloor that is likely a piece of a larger tectonic plate that broke off and slipped into the depths 250 million years ago.
Scientists mapped the structure, finding that it was unusually thicker and cooler than the surrounding areas.
The ancient seafloor challenges existing theories about Earth’s interior structure and provides new insights into how the planet’s surface evolved over millions of years.
New research has discovered evidence of an ancient seafloor that complicates current theories about Earths interior
The seafloor subducted beneath the Nazca plate roughly 250 million years ago
‘Our discovery opens up new questions about how the deep Earth influences what we see on the surface across vast distances and timescales,’ lead author and geology postdoctoral researcher Jingchuan Wang of the University of Maryland said in a statement.
One of the study’s key findings challenges prevailing ideas about what happens to oceanic slabs when they subduct into Earth’s mantle.
Researchers discovered the 12-mile-thick, 1,200-mile-long area in the ‘mantle transition zone,’ a region that separates the upper mantle from the lower mantle.
The prehistoric seafloor was found at the East Pacific Rise, a tectonic boundary on the floor of the southeastern Pacific Ocean.
‘This thickened area is like a fossilized fingerprint of an ancient piece of seafloor that subducted into the Earth approximately 250 million years ago,’ Wang said.
Subduction often leaves behind visible evidence of movement, such as volcanoes, earthquakes and deep marine trenches.
But usually, oceanic slabs are completely consumed by the Earth, leaving no discernable trace on the surface, Wang said.
His research challenges this idea. Wang and his colleagues found that material was moving through Earth’s interior much more slowly than previously thought.
The unusual thickness of the region the team discovered suggests the presence of colder material in this part of the mantle transition zone, and that some oceanic slabs get stuck halfway down as they subduct through the mantle.
‘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.
Therefore, his research shows that ancient subducted plates can be preserved deep within Earth’s interior, influencing mantle structures for hundreds of millions of years.
This new insight could prompt scientists to revise models of plate tectonics and gain a more accurate understanding of how Earth’s surface has evolved over geological timescales.
‘It’s giving us a glimpse into Earth’s past that we’ve never had before,’ Wang said.
The team also believes that the newly discovered seafloor could explain the Pacific Large Low Shear Velocity Province (LLSVP), a mysterious region of the lower mantle through with seismic waves travel more slowly than average.
The unusual structure of the LLSVP has long puzzled scientists. But now, Wang’s study has revealed that the ancient seafloor may have split the LLSVP like a wedge as it dropped into the mantle, offering a potential explanation for the province’s strange shape.
Wang and his team discovered this ancient seafloor through seismic imaging – a technique that allows researchers to collected data as seismic waves travel through different layers of the Earth.
The team suggested the seafloor was a piece of an ancient tectonic plate that broke off 250 million years ago and sank to the bottom of the Pacific Ocean, creating a new seafloor
‘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,’ Wang said.
This data allowed them to create a detailed map of this previously unknown structure hiding deep within Earth’s mantle, revealing the anomalous structure.
The researchers believe this long-lost seafloor may belong to the Phoenix plate, a tectonic plate that once dominated a large portion of the Pacific Ocean before it subducted beneath another oceanic plate.
As the Phoenix plate sunk deep into Earth’s interior, it carried cooler material from the ocean floor into the hot mantle. This left behind a cold thermal signature that Wang and his colleagues were able to detect in their research.
The team plans to extend their research to other areas of the Pacific Ocean and beyond, with a goal to create a more comprehensive map of ancient subduction and upwelling zones.
Upwelling is a geological process that occurs when subducted material heats up and rises back up to the surface.
They will also examine the effects that these zones have on structures both above and below Earth’s surface.
‘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.’