A new study reveals details of the composition and structure of the Earth's Inner Core

Seismological images have allowed us to discover details of the solid inner core of the Earth, something that is still a mystery today. The report indicates that the center of the planet could be in a state of thermal convection.

Earth's Core
Although human beings have managed to know the confines of the universe through our telescopes, or sent a ship that today already navigates in interstellar space, the nucleus of the planet still contains many secrets.

One of the ships sent into space, Voyager 1 managed to reach interstellar space, beyond Pluto. The most powerful telescopes have managed to rummage to distances in time close to the Big Bang. And not to mention the technology that has catapulted communications and development. But even so, there is still a lot to know and understand about the center of the Earth.

"Although the inner core of the Earth is commonly thought of as a solid sphere of iron, the most recent seismic observations suggest a slow flow of material, which has generated considerable interest and discussion" - Maurizio Mattesini, professor of Earth Physics at the Complutense University of Madrid.

Despite the considerable advances in seismology, mineral physics, geodynamics, paleomagnetism and mathematical geophysics, the structure and evolution of the Earth's internal core remain enigmatic. One of the most significant issues is its thermal history and the current thermal state. Several hypotheses have been proposed about an internal nucleus in thermal convection: a simple translational mode, of high viscosity, or a classical convection, of low viscosity, of the pencho type. A recent research published by Nature tries to move forward on these issues.

There, state-of-the-art seismic images were used to probe the outermost layer of the inner core for its isotropic compression speed and compare it with recently developed attenuation maps. The pattern that emerges in the resulting tomograms is interpreted with recent data on the viscosity of iron as the manifestation on the surface of the inner core of a thermally driven flow. A positive correlation was discovered between the compression rate and attenuation and temperature.

A breakthrough into the unknown

Although the convection of the outer nucleus controls the flow of heat through the boundary of the inner nucleus, the convection of the internal nucleus internally driven is a plausible model that explains a series of observations for the inner nucleus, including a distinctive anisotropy in the innermost inner nucleus.Anisotropy is the general property of matter according to which qualities such as elasticity, temperature, conductivity, and speed of propagation of light, vary according to the direction in which they are examined.

Earth Core
Images obtained from the inner core of the Earth by analyzing seismic waves. Image: Hrvoje Tkalčić - Scientific Reports

Motivated by the existing controversies regarding the behavior of the inner core (inner core CI), recent advances in seismic tomography were used to probe the outermost 100-kilometer layer of the CI in search of its compression wave velocity. The scheme uses a rigorous treatment of uncertainty applied to data obtained with a relatively scarce volumetric sampling, especially in the southern hemisphere.

The study was led by Hrvoje Tkalčić of the National University of Australia, with the collaboration of the Complutense University of Madrid. In conclusion, until now it was believed that the inner core of the Earth was a solid sphere of iron. However, and as Sinc reports, scientists have suggested the existence of a more static central region, where convection has almost ceased, and an external one where the material flows.

Several theories and many doubts

When analyzing all the available information, it was concluded that the solid inner core of the Earth could be in a state of thermal convection, a process by which heat is transferred that is produced in fluids due to temperature differences. This information was obtained by seismological images, experimental results at high pressure and temperature, and numerical simulations.

Tomogram
Tomograms of the compression rate and uncertainty in the outermost nucleus. Image: Scientific Reports.

Maurizio Mattesini, professor of Earth Physics at the Complutense University of Madrid, points out to Sinc that "although the inner core is commonly thought of as a solid iron sphere, the most recent seismic observations suggest a slow flow of material, which has generated considerable interest and discussion." These results have made it possible to obtain a clearer image of the Earth's internal core.

According to the researchers, it apparently consists of a more stagnant central part, where the convection has almost been extinguished, and a more external part in which thermal flows continue to drive the movement of the material, with a speed that can vary between 0.3 and 300 m/year. This new small nucleus within the internal core, of which very little is known, would be the last piece that would complete the parts of the deepest sector of our planet.