A high-resolution geological map of Earth's Southern Hemisphere has uncovered an unexpected feature: an ancient ocean floor located around 1,800 miles (2,900 kilometres) beneath the surface, near the core-mantle boundary (CMB). This thin but dense layer was discovered using seismic data collected from earthquakes in the Southern Hemisphere and analysed by researchers from the University of Alabama and Arizona State University.
Seismic earthquake waves were used to probe the Earth's interior structure, revealing regions with slower-moving waves known as ultralow velocity zones (ULVZs) at the CMB. These ULVZs are thought to be ancient oceanic crust that has been buried over millions of years.
The researchers' analysis suggests that these ULVZs may represent oceanic crust transported to their current location by convection currents within the Earth's mantle rather than being close to recognised subduction zones on the surface where tectonic plates push rock down into the Earth's interior. This hypothesis aligns with the simulations presented in the study.
While the thickness of the ancient oceanic crust varies, ranging from a few kilometres to tens of kilometres, it is challenging to ascertain whether it wraps entirely around the Earth's core due to its thinness. Future seismic surveys will provide more insight into this intriguing geological feature.
Understanding the Earth's interior structure in such detail has important implications for various geological processes, including heat transfer between the core and mantle. The composition differences between these layers are substantial and play a crucial role in shaping the planet's dynamics.
Overall, this discovery highlights the complexity of the Earth's interior and the potential for unexpected geological features beneath our feet. It underscores the importance of high-resolution mapping to gain insights into the processes that have shaped our planet over millions of years.