14 DAY TRIAL // The Earth's mantle can stretch up to 2,900 kilometers below the surface, thus the only way to study it is to conduct measurements on the speed of seismic waves which travel through it, in order to determine the rough composition and density. However, a new research conducted relatively recently has shown that against general belief these seismic waves travel with slower speeds through the lower regions because the crust is softer than the top one.
While pressures can reach as high as 230,000 times that of the atmosphere, what could cause a drop in density? The leader of the study, Alexander Goncharov from the Carnigie Institution's Geophysical Laboratory argues that weird electronic characteristics of the matter might be responsible for such processes. At such pressures and temperatures that range between 1,800 to 4,000 Kelvin, any material on the surface would be forced into an unrecognizable state.
Iron is one of the most abundant chemical elements on Earth and, while in the crust, it can form two distinct types of mineral, ferropericlase and perovskite. The research team believes that the electron configuration in ferropericlase creates a spin-transition zone in the lower regions of the mantle.
Goncharov explains that electrons which are not paired with other electrons experience a high-spin state, while the paired electrons are in a low-spin state. This affects the conductivity, chemical composition and general density of the material. The team was able to accurately determine that the ferropericlase mineral creates a change in crust density by modifying the pressure between the layers with high-spin and low-spin material.
Speed measurements of the wave propagating through the crust revealed that the density changes determine variations in pressure ranging between 395,000 up to 590,000 atmospheres, making the lower part of the crust appear less dense because acoustic wave travel at lower speeds. Furthermore, the properties of the matter are greatly affected by temperature variation. The findings contest the current theory regarding this specific region of the Earth's crust.