A groundbreaking high-resolution map of the Earth’s Southern Hemisphere has revealed a previously unknown ancient ocean floor that may encircle the planet’s core. This thin yet dense layer, located around 2,900 kilometers (1,800 miles) beneath the surface, lies at the core-mantle boundary (CMB) where the molten outer core meets the rocky mantle.
“Seismic investigations, such as ours, provide the highest resolution imaging of the interior structure of our planet, and we are finding that this structure is vastly more complicated than once thought,” said Samantha Hansen, a geologist from the University of Alabama, announcing the findings published in 2023.
Understanding the intricate geology beneath our feet is crucial for studying phenomena such as volcanic eruptions and variations in Earth’s magnetic field, which shields us from solar radiation. Hansen and her team used 15 monitoring stations buried in Antarctica’s ice to map seismic waves from earthquakes over three years. These waves reveal the composition of Earth’s interior, with slower-moving waves indicating ultralow velocity zones (ULVZs).
“Analyzing thousands of seismic recordings from Antarctica, our high-definition imaging method found thin anomalous zones of material at the CMB everywhere we probed,” explained Edward Garnero, a geophysicist from Arizona State University. “The material’s thickness varies from a few kilometers to tens of kilometers, suggesting we are seeing mountains on the core, in some places up to five times taller than Mt. Everest.”
The researchers propose that these ULVZs are most likely remnants of ancient oceanic crust buried over millions of years. Although not near known subduction zones, simulations suggest mantle convection currents could have transported the ocean floor to its current depth.
The study, published in Science Advances, indicates that this sunken ocean crust might encircle the entire core. However, its thinness makes it difficult to confirm. Future seismic surveys are expected to enhance our understanding of these structures.
This discovery aids geologists in comprehending how heat from the dense core escapes into the mantle, given the significant compositional differences between these layers. “Our research provides important connections between shallow and deep Earth structure and the overall processes driving our planet,” said Hansen.
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