The internal structure of the planet has just added another enigma to its long list of unanswered questions. A type of tomography of the Earth’s interior revealed that beneath oceans and continents there are patches or structures that are notably different from the crystallized rocks that should make up the entire mantle.
A group of geologists and geophysicists from ETH Zurich and the California Institute of Technology detected anomalous cold materials within the Earth’s lower mantle. This inner layer is approximately 3,000 kilometers thick, with temperatures ranging between 3,000 and 3,700 °C, and connects directly to the core of the planet.
Although the plates are everywhere, scientists can’t pinpoint what material they are made of or how they got there in the first place. Until now it was assumed that the mantle was composed of crystalline structures of magnesium silicate and iron oxide. However, the study published in Nature Scientific Reports points to other components of unknown nature.
There is no way for scientists to directly see inside the planet. The deepest hole dug by humanity, made in 1989 in Russia, reached only 12 kilometers deep. The heat given off by the project was intolerable for people and machinery. The distance achieved in Russia represents, at most, 10% of the kilometers necessary to reach the Earth’s lower mantle.
To compensate for this observation problem, geophysicists measure and “listen” to how they move seismic waves when they propagate in the subsoil. Depending on the composition and strength of the materials in the crust, mantle and core, these signals can travel more or less quickly, or even bounce off each other.
There are now better technologies to listen to “the Earth’s interior” and model the behavior of the layers. For the recent study they used the Piz Daint supercomputer to process data from each type of recorded seismic wave. These new high-resolution methods suggest that beneath the crust there are some kind of plate tectonic structures. The surprise is that such waste should not be in that area of the planet. They even appear in regions far from plate collisions and upwellings, such as in the Pacific Ocean.
“It could be ancient silica-rich material that has been there since the formation of the mantle about 4 billion years ago and has survived despite convective movements in the mantle, or areas where iron-rich rocks accumulate as a consequence of these movements of the mantle for billions of years,” said Thomas Schouten, co-author of the study.
Earth’s mantle was one of the first layers to form approximately 4.5 billion years ago. As the planet accumulated material, the rocks inside began to divide into layers based on their density. Denser materials, such as iron and nickel, sank toward the core to melt, while lighter materials, such as silicates, rose.
The mantle is fundamental to understanding the current dynamics of the planet’s surface. Convection of rocks in this layer drives plate tectonics, the movement of continents, and geological phenomena such as volcanism and earthquakes.
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