According to Stanford researchers, the reaction between seawater and iron in the Earth’s core can explain the formation of mysterious patches in Earth’s interior.
These mysterious patches are actually dense rocks which are located about 1,800 miles beneath Earth’s surface that dampen passing seismic waves. For decades, these patches have confounded scientists as they separate the planet’s molten metal heart from its rocky shell.
They stand out from their surroundings because seismic waves generated by earthquakes are slowed down by a tenth to a third of their normal speeds as they sweep across.
Moreover, the regions with ultra-low velocity zones or ULVZs stimulates as the Earth’s core and mantle interact to a much greater extent.
Study leader Wendy Mao said, “Aside from being a scientific anomaly, these dampening zones could also provide insights into other deep Earth processes.”
“There’s also evidence that ULVZs are the origins of molten plumes that feed volcanoes at the surface. So ULVZs could hint at much greater cycling between the core, mantle, and surface of Earth than we thought.”
in their new study, scientists have proposed a mechanism based on a new type of oxygen-rich iron compound. This compound has actually occurred under the conditions like those found in Earth’s lowermost mantle region.
During experiments, scientists compressed silvers of iron foil suspended in pure water to about 90 gigapascals. They then laser heated them to 3,000–4,000 degrees Fahrenheit. In result, they obtained a super-oxygenated form of iron that is packed with about a third more oxygen molecules.
Next, they checked whether their compound is able to share many of the seismic wave-dampening properties or not.
Study first author Jin Liu said, “The low sound speeds we calculated for our compound match very well what is observed seismically in ULVZs. This reaction requires only iron and water. As long as you have these components and the right temperature and pressure conditions, this compound likes to form.”
“Only a relatively small amount of subducted water would be needed to explain the zones. If just one-tenth of the mass of water in Earth’s oceans found its way to the core-mantle boundary over geologic time, it would be sufficient.”