Beneath our feet, at a staggering depth of 5,150 kilometers, something unexpected is happening—Earth’s inner core is subtly shifting its shape. New research published in Nature suggests that while the core is solid, its surface is not as rigid as once thought. Instead, it appears to be slowly reshaping itself, accumulating material in some areas while eroding in others—almost like the formation of hills and valleys.
A Core That’s in Motion
Led by seismologist John Vidale from the University of Southern California, the study analyzed seismic waves from earthquakes passing through the boundary of the inner core. These waves revealed that even when the core returns to a previously observed position, minute structural changes continue to occur.
The likely culprit? Dynamic flows in the outer core—a molten sea of iron and nickel that surrounds the solid inner core. These swirling currents interact with the inner core’s surface, subtly reshaping its landscape over time.
The Inner Core: Solid, But Not Rigid
While the inner core is mostly solid iron and nickel, it’s not an unyielding mass. Every year, a thin layer of molten outer core crystallizes and adds to the inner core’s structure, growing at a rate of about one millimeter per year.
However, this process is not uniform—some regions accumulate more material than others, leading to variations in shape. The deformations may range from hundreds of meters to several hundred kilometers, making it one of the most mysterious shifting landscapes on Earth.
A Core That Changes Speed, Too
This isn’t the first surprising discovery about the core. Previous research by Vidale’s team found that the inner core doesn’t spin at a constant rate.
- Until 2010, it was spinning faster than the rest of the planet.
- After that, it began to slow down.
- Today, it’s rotating more slowly than Earth’s surface.
These changes, though subtle, may slightly affect Earth’s day length—but not enough for us to notice without precise scientific instruments.
How Scientists Study Something We Can’t See
Since directly observing the core is impossible, scientists rely on seismic waves from earthquakes to study it. These waves travel through the core and can be compared across different years to detect changes.
Last year, researchers examined over 100 seismic signals from earthquakes occurring between North America and the South Sandwich Islands in the South Atlantic. By tracking how long the waves took to pass through the inner core, they uncovered its shifting rotation speed.
Now, in this latest study, they compared signals when the inner core was in the same position and found tiny inconsistencies. These small variations indicate that the core’s surface is not static—it’s subtly reshaping itself over time.
Why This Matters
According to geophysicist Jessica Irving, these core deformations have little direct impact on daily life. However, they offer critical insights into Earth’s internal structure and the geodynamo process that powers our planet’s magnetic field.
Although the core’s rotation slightly affects the length of a day, the difference is so small that humans wouldn’t perceive it—only advanced scientific measurements can detect the change.
Ultimately, understanding these subtle shifts in the core’s shape and movement brings us closer to unraveling the deep, hidden forces shaping our planet.
