(ORDO NEWS) — The Earth’s core, the deepest layer of our planet, is characterized by extremely high pressure and temperature. It consists of a liquid outer core and a solid inner core.
The inner core was formed and grows by solidification of liquid iron at the boundary of the inner core. The inner core has a lower density than pure iron, so it is believed that some light elements are present in its composition.
In a new study, scientists led by Professor He Yu from the Institute of Geochemistry of the Chinese Academy of Sciences found that the Earth’s inner core is not an ordinary solid, but consists of a solid iron sublattice in which light elements move like a liquid – a state known as the superionic state.
Liquid-like light elements within the iron sublattice exhibit high diffusion coefficients under the conditions of the inner core.
The superionic state, which is an intermediate state between the solid and liquid states, is widespread when it comes to the interior of planets.
Using high pressure and temperature numerical simulations based on the theory of quantum mechanics, the researchers found that some alloys of the Fe-H, Fe-C and Fe-O systems transitioned to the superionic state under conditions consistent with those of the Earth’s inner core.
In superionic iron alloys, light elements become disordered and diffuse, as in a liquid, in the crystal lattice. At the same time, the iron atoms that form the lattice remain ordered and vibrate relative to their positions in the lattice, forming a rigid framework.
The diffusion coefficients of C, H, and O atoms in superionic iron alloys are close to the diffusion coefficients of these elements in liquid iron.
One of the problems with the inner core is that it is too soft and has a rather low shear wave velocity. The researchers calculated the propagation velocities of seismic waves in such superionic iron alloys and found a significant reduction in shear wave velocity.
“Our results are in good agreement with the results of seismic observations. Elements that behave like a liquid give the core this “softness,” said co-author Sun Shichuan.
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