Earth’s Core Appears to Be Wrapped in an Ancient Structure Previously Unimagined

The highest-resolution map of the geological structure of Earth’s Southern Hemisphere has revealed an unexpected discovery: a relic of ancient oceanic crust that possibly encircles the planet’s core.

According to research published in April, this thin yet dense layer lies at a depth of approximately 2,900 km beneath the Earth’s surface. At this depth, the molten metallic outer core meets the rocky mantle above, marking the boundary between the core and mantle.

“Seismic studies like ours provide high-resolution imaging of the Earth’s inner structure, and we find that this structure is far more complex than previously thought,” stated geologist Samantha Hansen from the University of Alabama when announcing the research findings.

Understanding the intricate details beneath our feet is crucial for studying various phenomena, from volcanic eruptions to changes in Earth’s magnetic field, which shields us from solar radiation in space.

Hansen and her colleagues used 15 ice-embedded monitoring stations in Antarctica to map seismic waves from earthquakes over three years. The way these waves propagate and reflect provides insights into the composition of materials inside the Earth. Areas where seismic waves travel more slowly are known as Ultra-Low-Velocity Zones (ULVZs).

“By analyzing thousands of seismic records from Antarctica, our high-resolution visualization method detected thin anomalous patches of material at the core-mantle boundary everywhere we probed,” said geophysicist Edward Garnero from the University of Arizona.

The thickness of these materials varies from a few units to tens of kilometers. This suggests we’re seeing ‘mountains’ on the core, some in places five times the height of Mount Everest.

These ULVZs are thought to represent submerged oceanic crust that has been buried for millions of years.

Although this submerged crust is not located near recognized subduction zones on the Earth’s surface—regions where shifting tectonic plates push rock down into the Earth’s interior—the modeling presented in the research shows how convective currents could have shifted ancient oceanic crust to its current location.

Building assumptions about the types and movement of rock at the core-mantle boundary based on seismic wave propagation is complex, and researchers do not rule out other explanations for the observed effects. Nevertheless, the hypothesis of ancient oceanic crust is currently the most plausible explanation for these ULVZs.

There’s also speculation that this ancient oceanic crust could encircle the entire core, although its thinness makes this difficult to confirm. Future seismic research will further refine the overall picture.

One of the areas where this discovery may assist geologists is in understanding how heat from the hotter, denser core escapes into the mantle. The differences in composition between these two layers are greater than those between solid surface rocks and the air above, providing insights into the inner workings of our planet.

“Our study allows us to establish important connections between surface and deep Earth structure and the overarching processes that drive our planet,” Hansen commented.