doi.org/10.1093/nsr/nwaf419
Credibility: 989
#Core
At the heart of our planet, more than 5,000 kilometers deep, lies an extremely compact solid ball of iron called the inner core
Despite being solid, it has always intrigued scientists because of its strange behavior: it is much “softer” than it should be.
Seismic waves that pass through this region travel slower than expected for such a hard metal, and some of its properties are more reminiscent of butter than steel.
For decades, no one could explain why the Earth’s core was both firm and surprisingly flexible.
Now, Chinese research published in the National Science Review has provided the answer: the inner core is not an ordinary solid.
It is in a special state called superionic, where light atoms – in this case, mainly carbon – move as if they were liquids within an iron structure that remains rigid and organized.
It’s as if the iron forms a fixed grid and the carbon dances freely between the “holes” in this grid, making the entire material softer.
Scientists led by professors Youjun Zhang, from Sichuan University, and Yu He, from the Institute of Geochemistry of the Chinese Academy of Sciences, managed to reproduce in the laboratory the extreme conditions of the inner core: pressures more than 3 million times the atmospheric pressure of the surface and temperatures of almost 6,000 degrees Celsius, similar to the surface of the Sun.
To do this, they fired samples of iron-carbon alloy at more than 7 kilometers per second using a dynamic shock platform.
The results were impressive.
When the pressure and heat reach the level of the inner core, the carbon atoms begin to circulate rapidly through the crystalline structure of the iron, which remains solid.
This movement makes the material much less rigid, drastically reduces the speed of shear waves (the “S” waves of earthquakes) and increases Poisson’s ratio – exactly what seismologists observe when they look at the center of the Earth.
For the first time, we have experimental proof that the Earth’s inner core is in this superionic state.
Previously, only computer simulations suggested this possibility; now, experiments confirm it.
This discovery goes far beyond solving an old enigma.
It changes our view of what happens deep within the planet.
The almost liquid movement of light elements may help explain why seismic waves behave differently depending on the direction in which they travel – a phenomenon called seismic anisotropy.
More importantly, this “dancing” of carbon atoms may be an extra source of energy that helps keep the Earth’s magnetic field functioning.
In addition to the thermal and chemical convection we already knew, we now have atomic diffusion as a third engine for the geomagnetic dynamo that protects our planet from solar radiation.
The researchers also show that the carbon present in the core is probably not forming separate compounds or replacing iron atoms in the structure, but rather occupying the spaces between them – the so-called interstitial state.
It was precisely this detail that previous studies had overlooked.
In short, we’ve stopped imagining the inner core as a static, rigid ball of iron.
It is, in fact, a dynamic place, almost alive at the atomic level, where iron stays in place and carbon circulates like people in a crowded square.
This new understanding isn’t just useful for Earth: it can explain how other rocky planets and even exoplanets generate their magnetic fields and evolve over time.
What seemed like an unsolvable mystery about the heart of our planet ended up revealing a completely new state of matter – hidden right beneath our feet.
Published in 12/04/2025 21h48
Text adapted by AI (Grok) and translated via Google API in the English version. Images from public image libraries or credits in the caption. Information about DOI, author and institution can be found in the body of the article.
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