At the center of the Earth, over 5,000 kilometers deep, there is a solid sphere made largely of iron. It’s the inner coreand it is fundamental for life on the planet: it powers the magnetic field that protects us from solar radiation and the heat that rises from there moves the tectonic plates, shaping continents and oceans.
Yet, how hot it is nor when it began to cool and solidify. All we can do is observe indirectlywith the data that comes to us from earthquakes and laboratory experiments.
Now, a new study led by Alfred Wilson-Spencer, a researcher in mineral physics at the University of Leeds, has opened a new way to understand what’s really down there. And the unexpected protagonist is carbon.
The Earth’s core is made up of two parts: a solid internal one and a liquid external one. The boundary between the two is the point at which matter changes from liquid to solid. So, if we can understand at what temperature does the nucleus meltwe can also understand how it’s made.
To do this, scientists rely on two main tools: meteorites And seismology.
Meteorites tell us about the composition of primordial planets and suggest what the core should contain iron, nickeland maybe small quantities of silicon or sulphur. But their information is too general.
Seismology, however, tells us how fast seismic waves travel within the Earthand these speeds change depending on the material they pass through. Thanks to this data, we know that the inner core is less dense than pure ironand that the liquid core is denser than solida rather strange thing.
These observations tell us that it must be in the nucleus more than one chemical elementbut to tell us which ones exactly.
The discovery
To overcome these limitations, the Leeds team looked at the problem from a new point of view: super-refrigeration. It is a phenomenon that occurs when a liquid cools below its freezing temperature without immediately becoming solid. It’s the same principle whereby bottled water can remain liquid even at -5°C, but can suddenly freeze as soon as you shake it.
Applying this concept to molten metals of the earth’s coreresearchers found that pure iron needs to cool to at least 1,000°C below its melting point to begin to solidify. But this is it impossible: If this were indeed the case, the inner core would be much larger than seismic data shows, or even completely solid.
Adding silicon or sulphurthe result gets worse: even more super-refrigeration is needed.
The turning point comes with the carbon: with only 2.4% carbon in the mass of the nucleus, they are enough approximately 420 °C of super-refrigeration to begin solidification. And with the 3.8%they barely need it 266°C. High values, yes, but credible.
The core is not just iron
This discovery demonstrates for the first time that the The presence of carbon makes the formation of the inner nucleus physically possible. And this represents a decisive step to understand what the interior of the Earth is really like.
But there is another aspect to consider: seismic data tell us that iron and carbon are not enough. The nucleus must contain at least one other element to explain its density. The researchers hypothesize that it is oxygen and maybe even of silicon.
We are still far from a definitive answer, but this new perspective tightens the circle about possible chemical combinations and brings science one step closer to the truth about what’s deep inside the Earth.
