Earth's core isn't static, but changes shape (and scientists are beginning to understand why)

©NASA via Unsplash

For years, we have imagined Earth's center as immobile: a compact, silent sphere hidden under thousands of miles of rock and molten metals. In textbooks, Earth's inner core is often described as a static, stable mass, almost as if it had crystallized over time. A fixed point in a planet that on the surface, on the contrary, never stops changing.

Reality, however, turns out to be a lot more complex. New scientific research suggests that far from being static, the heart of our planet is subject to slow, profound changes. Scientists have seen that the surface of the core can deform over time, as if that giant metal sphere can adjust its shape.

This is a surprising discovery that opens up an entirely new scenario: the center of the Earth turns out to be much more dynamic than we previously thought. Understanding what happens down there can help us better understand the evolution of the planet, the workings of the Earth's magnetic field and even certain aspects of Earth's rotation. And as technology continues to improve, researchers are slowly but surely succeeding in deciphering signals coming from almost unimaginable depths.

How Earth's interior is constructed

To understand why this discovery is so important, we need to take a small imaginary journey into the planet's interior. Earth consists of four main major layers: the crust, the mantle, the outer core and the inner core. A complex structure reminiscent of a giant pie with multiple layers, each with very different physical properties.

Earth's crust is the most superficial and thinnest layer, the layer on which we live. It's not a bordering surface, but a mosaic of large tectonic plates that move slowly. In the long run, these movements, almost invisible on human time scales, are responsible for earthquakes, volcanic eruptions and the formation of mountains.

Beneath the crust extends the mantle, a nearly 3,000-kilometer-thick layer of extremely hot and dense rock. There, the material isn't completely liquid, but neither is it rigid: it flows slowly, in a continuous process that drives the dynamics of the tectonic plates.

If you go even deeper, you get to the outer core, which consists mainly of liquid iron and nickel. This molten metal is in constant motion and it's precisely from this gigantic vortex that the Earth's magnetic field, the invisible shield that protects the Earth from solar radiation and makes life possible as we know it, is created.

Finally, at the very center of the planet is Earth's inner core, a solid sphere composed mainly of iron and nickel. The temperature here rises to more than 5,000 degrees Celsius, similar to the temperature on the surface of the sun. Yet the material remains solid. The reason is simple: the pressure of the layers above is so enormous that the metal cannot melt.

Of course, no one has ever been able to reach these depths directly. Scientists study the planet's interior from seismic waves generated by earthquakes. Those waves travel through the Earth and change their behavior depending on the materials they encounter along the way. It's precisely by analyzing these signals that the new discovery has come to light.

Earth's core changes shape

Earth's inner core lies about 4,800 kilometers below the surface. For decades, it was considered an extremely stable structure, virtually unchanging over time. New analyses, however, paint a very different picture.

Researchers were trying to better understand how the core rotates relative to the rest of the planet. Some observations seemed to indicate that the rotation slowed down relative to Earth, only to accelerate again around 2010. To investigate this phenomenon, the researchers scrutinized decades of seismic data, paying special attention to signals from numerous earthquakes that occurred between 1991 and 2024 near the South Sandwich Islands, in the Antarctic region.

The seismic waves generated by these earthquakes traveled right through the planet's core before being recorded by monitoring stations scattered around the globe. By carefully analyzing these waves, scientists discovered some anomalous signals that could not be explained by traditional geological models.

Certain waveforms showed completely new characteristics. Further analyses led to a surprising conclusion: the surface of the core can slowly change shape over time. The data indicate that the outer layer of the core undergoes viscous deformations caused by the extreme pressure and interaction with the liquid outer core surrounding it.

In other words, Earth's core does not appear to be a perfectly rigid block. Rather, it may behave as a structure that slowly deforms under the influence of the forces operating at great depths within the planet. According to Professor John Vidale, who led the research, some parts of the core surface may have been deformed by more than a hundred meters.

The role of the turbulent outer core

A crucial element in this discovery is the interaction between the inner core and the liquid outer core. The latter consists of molten metal constantly moving in large, turbulent flows. For a long time, scientists assumed that these movements could not directly affect the inner core on relatively short time scales.

However, the new observations suggest that turbulence in the outer core may exert pressure on the surface of the inner core, leading to gradual deformations over a period of years. These dynamics may also have important implications for our understanding of the Earth's magnetic field.

In recent decades, researchers have observed sudden changes in the structure of the magnetic field, phenomena known as 'geomagnetic jerks', or geomagnetic shocks. Some scientists suspect that these variations are directly related to the processes occurring at the boundary between inner core and outer core. Understanding what happens at the heart of the planet could improve scientific models that describe magnetic field generation, Earth's internal dynamics and even long-term climate stability.

This discovery underscores how little we actually still know about the depths of our planet. Earth's inner core, which for decades we saw as an immobile solid mass, now looms as a vibrant structure, subject to slow but constant change.

Many questions remain unanswered. Scientists are trying to figure out what forces drive these changes, how fast they occur and whether similar processes can occur in other planets or celestial bodies. One thing is clear: As seismic technology becomes increasingly precise, Earth's center ceases to be an unattainable mystery. Step by step, it's becoming a new frontier for scientific research.

(©Nature Geoscience via GreenMe.it 2026 / Managing Editor: Julie Morgan - The Press Junction / Picture: ©NASA via Unsplash)