A new study, developed by a team of American and Chinese researchers and published in the journal Natureexplains how two huge ones could have originated “islands” as big as continentsmade up of hot and dense rocky masses with anomalous chemical composition, which are found in the Earth’s mantle at about 2900 km depth near the border with the nucleus. The origin of these areas, located one below theAfrica and the other underPacific Ocean and known how LLSVP (Large Low Seismic Velocity Provinces or “Large Provinces with Low Seismic Speed”), could be linked to migration of material from the nucleus during early stages of Earth formation. These structures may have contributed to thehabitability of the Earth.
The origin of the two “thesun” ancient in the earth’s mantle
LLSVPs are rock masses warmer and older of the surrounding mantle materials, which were discovered in the 1990s by studying the behavior of seismic waves generated by earthquakes: when they encounter these areas as they propagate within the Earth, the waves slow down due to their high temperature and different chemical composition. These masses do not participate in the movements that mix the materials of the Earth’s mantle, but they remain isolated conserving heat. Many hypotheses about the origin of LLSVP have been developed in recent years, but researchers may now have found a more comprehensive explanation.
About 4.5 billion years agothe Earth presented a magma oceana hot, molten layer above the core-mantle boundary. This ocean gradually cooled, and denser, heavier materials migrated downwards, while less dense, lighter materials migrated upwards. One would therefore expect the mantle to be made up of well-defined layers with different chemical composition and density, but the new study highlights that this is not the case. At the base of the mantle there are the LLSVPs that form irregular accumulations, with others at the edges thin structures (calls ULVZ or Ultra-Low Velocity Zones) where the seismic velocity is even lower. According to the researchers, the Earth’s coresubjected to enormous pressure, would have released material containing lighter elements such as silicon and magnesium. This material would have risen upwards, mixing with the mantle materials, preventing the formation of clear layers. This transfer of light elements would explain the different chemical composition of the LLSVPs and ULVZs.
Why it is important to know the LLSVPs
Obtaining new information on LLSVPs is important, not only for a better understanding of the structure of our planet, but also for other reasons. LLSVPs could be at the origin of thevolcano activity located at a certain distance from the margins of lithospheric plates. In fact, researchers believe that from these masses “plumes” of hot material rise to the surface, such as those that fuel the volcanoes of Hawaii. Furthermore, core-mantle interactions may have influenced the cooling of the Earth and even the evolution of the atmosphere. Some studies highlight that the “islands” of the mantle would have contributed to the origin and dynamics of tectonic plateswhose movements also affect the climate and consequently thehabitability of the Earth.
