A new discovery in October 2025 has revealed that Earth’s inner core may be rotating at a different speed than the rest of the planet—challenging long-held assumptions about our planet’s internal dynamics and sparking a scientific debate that could reshape geophysics.
We thought we knew how Earth moved. We were wrong.
For decades, scientists believed that Earth’s inner core—a solid ball of iron and nickel roughly the size of the Moon—rotated in sync with the rest of the planet, or slightly faster. But in October 2025, a team of seismologists from the University of Beijing and Caltech published a study that upended this assumption.
Using seismic wave data from earthquakes spanning the last 60 years, they found that Earth’s inner core may have slowed down—and could now be rotating more slowly than the mantle and crust above it. This revelation has profound implications for our understanding of Earth’s magnetic field, tectonic activity, and even the planet’s long-term stability.
The Science Behind the Spin
The inner core is surrounded by a liquid outer core, which in turn is encased by the mantle and crust. Seismic waves generated by earthquakes travel through these layers, and by analyzing their travel times and paths, scientists can infer how the inner core behaves.
Here’s what the new data shows:
- Between 1960 and 2000, the inner core appeared to rotate slightly faster than the rest of the planet.
- Since 2009, that rotation has slowed—and may now be lagging behind the mantle.
- The shift is subtle, but measurable: a few tenths of a degree per year.
This change could be part of a natural oscillation cycle, possibly spanning 60–70 years. But it also raises questions about what drives the core’s motion—and whether external forces, like gravitational interactions with the Moon or changes in Earth’s magnetic field, play a role.
The inner core isn’t just a passive lump of metal. It’s crucial to Earth’s magnetic field, which protects us from solar radiation and helps guide migratory animals. If the core’s rotation changes, it could:
- Affect the strength and orientation of the magnetic field.
- Influence tectonic plate movement and volcanic activity.
- Alter the length of Earth’s day by tiny fractions of a second.
Some researchers even speculate that these shifts could be linked to climate cycles, though that connection remains controversial.
A Planet Still Full of Surprises
We often think of Earth as stable, predictable. But this discovery reminds us that beneath our feet, the planet is alive with motion—and that even its deepest layers are still revealing secrets.