A high-resolution map of Earth's Southern Hemisphere has unveiled an unexpected discovery: an ancient ocean floor located around 2,900 kilometres (1,800 miles) below the surface, potentially wrapping around the core. This discovery was made through seismic investigations conducted by geologists using 15 monitoring stations in Antarctica.
Seismic waves generated by earthquakes were used to map the composition of Earth's interior, revealing regions where these waves moved more slowly, known as ultralow velocity zones (ULVZs). The researchers found thin anomalous zones of material at the core-mantle boundary (CMB), suggesting the presence of sunken oceanic crust. Some of these ULVZs were estimated to be up to five times taller than Mount Everest.
The researchers propose that over millions of years, convection currents within Earth's mantle may have shifted this ancient ocean floor to its current position, even though it is not close to recognized subduction zones where tectonic plates converge and push material into Earth's interior. While they consider other possibilities, such as rock types and movement variations, the ocean floor hypothesis seems the most plausible explanation for the current ULVZs.
Although it is challenging to confirm whether this ancient ocean crust encircles the entire core due to its thinness, future seismic surveys could provide more insights into its extent.
This discovery has implications for understanding heat transport from Earth's hot and dense core to the mantle. The differences in composition between these layers are more significant than those between the solid surface rock and the air above. This knowledge could contribute to a better understanding of geological processes, including volcanic eruptions and the Earth's magnetic field, which shields us from solar radiation.