Scientists have discovered two enormous structures deep within Earth’s mantle. Research from Utrecht University reveals these regions are hotter and older than the surrounding sunken tectonic plates—at least half a billion years old, possibly older.
This finding challenges the idea that Earth’s mantle is well-mixed and fast-flowing, suggesting less movement in the mantle than previously thought.
Large earthquakes make the Earth vibrate like a bell with different tones. Seismologists study these tones to understand Earth’s interior. If the tones are “out of tune” or quieter, it indicates anomalies, helping to create images of Earth’s interior, similar to X-rays for doctors.
At the end of the last century, scientists found two underground “super-continents” more than 2000 kilometers below the surface: one under Africa and one under the Pacific Ocean. These structures, called Large Low Seismic Velocity Provinces (LLSVPs), are located at the boundary between Earth’s core and mantle.
Seismic waves slow down in these hot regions like you can’t run as fast in hot weather.
Seismologists Deuss and Talavera-Soza added information about the “damping” of seismic waves, which is the energy loss as waves travel through Earth. They found little damping in LLSVPs, making tones sound loud there.
There was more damping in the cold slab graveyard, making tones soft. In the upper mantle, they expected the hot regions to have damped waves, similar to how you slow down and get tired faster in hot weather.
Mineral specialist Laura Cobden suggested studying the grain size of LLSVPs. Researcher Ulrich Faul said temperature alone can’t explain the low damping. Deuss explained that grain size is more important.
Subducting tectonic plates have small grains, leading to higher damping. Since LLSVPs have little damping, they must consist of larger grains.
These large grains don’t form quickly, indicating LLSVPs are much older than the surrounding slab graveyards. The LLSVPs are also very rigid, so they don’t participate in mantle convection, challenging the idea that the mantle is well-mixed. Talavera-Soza added that LLSVPs must survive mantle convection in some way.
Understanding the Earth’s mantle is crucial for studying our planet’s evolution and surface phenomena like volcanism and mountain building. The mantle drives these processes. For example, mantle plumes are large bubbles of hot material rising from deep within Earth, causing volcanic activity, like in Hawaii. Scientists believe these plumes originate at the edges of LLSVPs.
Seismologists study Earth’s interior using oscillations from large, deep earthquakes, like the 1994 Bolivia earthquake. These vibrations reveal damping (how loud they are) and wave speed (how out of tune they are). Thanks to high-quality seismometer records, researchers can use data from past earthquakes dating back to 1975.
Journal Reference:
- Talavera-Soza, S., Cobden, L., Faul, U.H. et al. Global 3D model of mantle attenuation using seismic normal modes. Nature (2025). DOI: 10.1038/s41586-024-08322-y
Source: Tech Explorist
