What does the Earth's core contain?

(Dan Tri) - The Earth's solid core is not only made of iron, but also contains carbon, oxygen and silicon. This discovery opens up the solution to the centuries-old mystery of how the core forms and maintains the magnetic field that protects life.

The Earth's core may not be made up of just iron, but it appears to contain carbon as well. New research has found it contains oxygen and silicon as well (photo: Getty Images).

The iron-rich core at the center of the Earth plays a key role in the planet’s evolution. It not only powers the magnetic field – the shield that protects the atmosphere and oceans from solar radiation – but also drives plate tectonics, constantly reshaping the continents.

Despite its importance, many fundamental properties of the core remain a mystery: how hot is it, what is it made of, and when did it start freezing? A recent discovery brings scientists closer to answering all three questions.

The temperature of the inner core is estimated to be around 5,000 Kelvin (4,727°C). Initially liquid, the core cools over time, crystallizing its solid interior and expanding outward. This release of heat creates plate tectonic currents.

The cooling is also the source of Earth's magnetic field. Much of the magnetic energy today is maintained by the freezing of the liquid outer core, which powers the solid central core.

However, without direct access, scientists are forced to rely on estimates to understand the cooling mechanism and properties of the core. To clarify that, the most important factor is determining its melting temperature.

Thanks to seismology – the study of earthquake waves – we know exactly where the boundary between the solid and liquid cores lies. The temperature at this boundary is also the melting point, the point at which freezing begins.

Therefore, if the melting temperature can be accurately determined, people will have a better understanding of the true temperature of the core and the chemical composition inside it.

Mysterious Chemistry

There are two main approaches to understanding the composition of the Earth's core: studying meteorites and analyzing seismic data.

Meteorites are considered to be the “remnants” of planets that have not yet formed or fragments from the cores of destroyed planets. Their chemical composition suggests that the Earth’s core is mainly composed of iron and nickel, possibly mixed with a few percent of silicon or sulfur. However, these data are only preliminary and not detailed enough to be definitive.

Seismology, on the other hand, offers a much more detailed view. Seismic waves from earthquakes travel through the Earth at different speeds depending on the material they pass through. By comparing the wave arrival times at measuring stations with experimental results of the speed of travel in minerals and metals, scientists can build models of the planet’s interior.

The results showed that the Earth's core is about 10% lighter than pure iron. In particular, the liquid outer core is denser than the solid inner core - a paradox that can only be explained by the presence of some minor elements.

But even with the range of possible compositions narrowed, the puzzle remains unsolved. Different scenarios yield melting temperatures that differ by hundreds of degrees Celsius, making it challenging to pinpoint the exact core properties.

A new restriction

In the new study, scientists used mineral physics to understand how the Earth's core began to freeze—a more specific approach than both meteorology and seismology.

Simulations show that as the atoms in a liquid metal crystallize into a solid, each alloy requires a different level of “supercooling,” or being lowered below its melting point. The more intense the process, the more likely the liquid will freeze.

For example, water in a freezer can be supercooled to -5°C for hours before freezing, while water droplets in clouds can turn into hail after just a few minutes at -30°C.

Calculations suggest that the core’s maximum supercooling is about 420°C below its melting point. If it were exceeded, the inner core would be unusually large compared to seismic data. Meanwhile, pure iron would need 1,000°C to crystallize, which is impossible because the entire core would have solidified.

Adding silicon or sulfur doesn't help either, and may even supercool the core further.

Only when carbon is considered does the picture make sense. If 2.4% of the core mass is carbon, it would take about 420°C to freeze the inner core; with 3.8% carbon, that drops to 266°C. A much more plausible figure. This is the first evidence that carbon plays a significant role in core crystallization.

The core, however, cannot be made up of just iron and carbon, as seismic data require at least one other element. Research suggests the core may also contain oxygen, and even silicon.

Source: https://dantri.com.vn/khoa-hoc/loi-trai-dat-chua-dung-nhung-gi-20250923025913011.htm