Ancient seafloor discovery reveals Earth’s deep history

University of Maryland scientists have made a groundbreaking ancient seafloor discovery, revealing evidence of a seafloor that sank deep into Earth during the age of dinosaurs. This finding challenges existing theories about Earth’s interior structure and provides new insights into the planet’s geological history. The ancient seafloor was uncovered in the East Pacific Rise, a tectonic plate boundary in the southeastern Pacific Ocean, through innovative seismic imaging techniques that allowed the researchers to peer deep into Earth’s mantle. The findings were published in Science Advances on September 27, 2024.

Led by postdoctoral researcher Jingchuan Wang, the team focused on a previously unstudied patch of the mantle transition zone, a region between 410 and 660 kilometers beneath the Earth’s surface. The transition zone acts as a boundary separating the upper and lower mantles, with its thickness influenced by temperature variations. Through their research, the scientists discovered an unusually thick area in this zone, which they believe is a remnant of the ancient seafloor discovery that had subducted into Earth approximately 250 million years ago.

Wang explained that subduction occurs when one tectonic plate is forced beneath another, recycling surface material back into the Earth’s interior. This process is responsible for the formation of geological features like volcanoes and marine trenches. However, unlike traditional subduction studies that focus on surface rock samples, Wang’s team used seismic waves to map the hidden structures deep within the mantle. By analyzing how these waves traveled through Earth, they were able to reconstruct detailed images of the seafloor’s ancient slab, which may also explain the structure of the Pacific Large Low Shear Velocity Province (LLSVP)—a massive region in the lower mantle.

The seismic imaging technique, which Wang likened to a CT scan, provided a new perspective on Earth’s deep interior. The ancient seafloor discovery showed that some oceanic slabs, instead of being fully consumed by the Earth, remain stuck in the mantle transition zone. This thickened area, described as a fossilized fingerprint, gave the team a rare glimpse into Earth’s geological past.

One surprising result of the study was the slow movement of material through Earth’s mantle. Wang noted that the discovered material was sinking at about half the expected speed, suggesting that the mantle transition zone could act as a barrier, slowing down the movement of tectonic plates. This finding opens new questions about the influence of deep Earth processes on surface geology across vast distances and time scales.

Looking to the future, the team plans to expand their research to other regions of the Pacific Ocean. Wang aims to create a comprehensive map of ancient subduction zones and their interactions with upwelling, a process where subducted material rises back to the surface after heating. This work will help improve models of tectonic plate movement over Earth’s history, revealing more hidden structures and further advancing the understanding of planetary geology.

This ancient seafloor discovery is just the beginning, according to Wang, who believes there are many more ancient structures waiting to be uncovered deep within the Earth. Each new discovery has the potential to provide fresh insights into Earth’s past and even offer clues about geological processes on other planets.

https://phys.org/news/2024-09-geologists-mysterious-subduction-zone-beneath.html