In a groundbreaking discovery, scientists have revealed a previously unknown feature beneath Earth’s Southern Hemisphere – an ancient ocean floor that may encircle the planet’s core. This remarkable finding stems from the most high-resolution geological mapping of the region to date, shedding light on the intricate and unexpected structures hidden beneath our planet’s surface.
Situated approximately 2,900 kilometers (1,800 miles) below the Earth’s surface, this thin yet dense layer marks the boundary between the molten, metallic outer core and the rocky mantle above it, known as the core-mantle boundary (CMB).
Geologist Samantha Hansen, from the University of Alabama, emphasized the significance of seismic investigations in unraveling Earth’s internal structure, stating, “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.”
Understanding the composition of the Earth’s interior is paramount for comprehending a range of phenomena, including volcanic eruptions and variations in the planet’s magnetic field, which shields us from solar radiation from space.
To uncover this geological mystery, Hansen and her team utilized 15 monitoring stations located beneath the Antarctic ice. Over a span of three years, they meticulously mapped seismic waves generated by earthquakes. The behavior of these waves, including their speed and reflections, offered insights into the Earth’s internal makeup.
The regions where seismic waves moved at a slower pace were identified as ultralow velocity zones (ULVZs). Geophysicist Edward Garnero from Arizona State University explained, “Analyzing [thousands] of seismic recordings from Antarctica, our high-definition imaging method found thin anomalous zones of material at the CMB everywhere we probed. The material’s thickness varies from a few kilometers to [tens] of kilometers. This suggests we are seeing mountains on the core, in some places up to five times taller than Mt. Everest.”
The researchers propose that these ULVZs likely consist of oceanic crust that has been buried over millions of years. While this submerged crust is not located near recognized subduction zones on the Earth’s surface (where tectonic plates push rock into the planet’s interior), simulations outlined in the study suggest that convection currents may have transported the ancient ocean floor to its current position.
Though interpretations based on seismic wave data are complex and subject to revision, the hypothesis of an ancient oceanic crust is currently the most plausible explanation for these ULVZs. There is even speculation that this thin layer of ancient oceanic crust might enfold the entire core, although its extreme thinness makes this difficult to confirm. Future seismic surveys are expected to provide further insights into this captivating geological enigma.
This discovery not only deepens our understanding of Earth’s internal dynamics but also helps scientists comprehend how heat from the core permeates into the mantle. The disparities in composition between these two layers are more profound than those between the solid surface rock and the atmosphere above, providing a critical link in the Earth’s complex geological processes.
As Hansen aptly puts it, “Our research provides important connections between shallow and deep Earth structure and the overall processes driving our planet.