Researchers applied a new method of analyzing seismic waves.
Deep within the Earth, scientists have discovered two giant structures the size of continents, which may be over half a billion years old. These mysterious formations, dubbed "islands," are hidden beneath the planet's surface at a depth of about 2000 kilometers, reports Earth.
According to research results from Utrecht University (Netherlands), published in the journal Nature, these structures are significantly hotter than the surrounding mantle. Moreover, their unique physical properties challenge established notions about the Earth's internal structure.
The focus is on two massive areas located deep in the mantle: one beneath Africa and the other beneath the Pacific Ocean. Their height reaches approximately 1000 kilometers, which is more than 100 times the height of Everest—the tallest mountain.
The article states that these formations were first recorded back in the late 20th century during seismic wave analysis. When powerful earthquakes occur, the Earth begins to oscillate like a bell. By analyzing these oscillations, seismologists can study the structure of the planet's interior.
This is how scientists discovered the anomalies now referred to as Large Low Seismic Velocity Provinces (LLSVPs). In these regions, seismic waves travel significantly slower due to the high temperature of the material.
"Graveyard" of Tectonic Plates
Surrounding these mysterious "islands" are so-called "graveyards" of tectonic plates. These are cold areas formed by tectonic plates that have sunk into the mantle as a result of the subduction process, where one tectonic plate descends beneath another.
These submerged plates gradually cool and accumulate in the depths of the mantle. That is why they are significantly colder than the surrounding environment.
Unexpected Research Results
To understand the nature of these structures, researchers applied a new method of analyzing seismic waves. In addition to measuring their propagation speed, they also assessed the degree of attenuation, that is, how much energy the wave loses as it passes through the material.
The results were unexpected. Scientists found that within LLSVPs, seismic waves lose almost no energy, even though these areas are hotter than the surrounding mantle. In contrast, significant attenuation is observed in the cold "graveyards" of tectonic plates.
According to the researchers, this indicates that the material structure in these regions is fundamentally different.
The Role of Mineral Grains
One of the key factors in this phenomenon may be the size of mineral grains in the rocks. In the cold submerged plates, minerals recrystallize into fine grains. As a result, seismic waves lose a lot of energy as they pass through numerous boundaries between the grains. In the mysterious "islands," however, the grains are likely significantly larger. This allows waves to pass through them almost without loss.
The scientists believe this may also explain their immense age. Since mineral grains grow very slowly, the formation of such structures could have taken hundreds of millions of years.
The material notes that the data obtained indicate that these areas do not actively participate in the convective processes of the mantle, meaning the movement of hot material that usually constantly stirs it.
