Earth's core changes speed: What does this mean for us?
The inner core, a massive iron ball the size of the moon, continues to rotate in the same direction as Earth, but occasionally changes its speed. A new study shows that this process has been observed for years and may be part of a recurring cycle.
For decades, Earth's inner core has been considered the planet's stable engine. Now, an international team from Peking University and the University of Southern California has discovered evidence that its rotation is not constant. A study in the journal Nature Geoscience shows that the Earth's core's speed slows or accelerates over years, but does not change direction . These fluctuations occur at intervals of several years to decades.
The discovery is based on the analysis of seismic waves generated during strong earthquakes that traverse the Earth's core. Their travel times changed over decades in a pattern that can only be explained by variations in the speed of the Earth's core rotation. Previous statements that spoke of a "reversal of direction" are therefore misleading.
The velocity fluctuations of the Earth's core indirectly influence the magnetic field, which protects us from cosmic radiation. Changes in the magnetic field can affect navigation using compasses, satellite systems, and power grids.
Even small fluctuations in the length of the day can affect high-precision measurement systems. Climatic effects are currently hypothetical but are being further investigated.
The inner core consists predominantly of solid iron and nickel, has a diameter of approximately 2,440 kilometers, and is surrounded by a liquid outer core. This interaction creates the magnetic field that protects life on Earth and enables numerous technological systems.
The discovery was only possible because earthquakes are natural "measuring instruments." Their shock waves permeate the entire planet, providing data on regions that would otherwise be inaccessible.
Researchers compare these records over decades and can reconstruct changes from them. The change in direction now observed was confirmed by systematic analyses of earthquake series in Alaska, Chile, and Indonesia.
Analyses of historical data suggest that similar fluctuations in the velocity of Earth's inner core may have occurred as early as the 1960s. If this rhythm is confirmed, the current observation period would not be a singular event, but part of a recurring pattern.
- Diameter: approx. 2,440 kilometers
- Depth: approximately 5,150 to 6,370 kilometers below the Earth's surface
- Composition: predominantly iron and nickel
- Temperature: estimated up to 6,000 degrees Celsius
- State: solid, surrounded by a liquid outer core
- Role: central to the generation of the Earth's magnetic field
*Editor's note: This article was revised on September 4, 2025, after re-examining the underlying study and consulting with Dr. Monika Korte , head of the "Earth's Magnetic Field Development" working group at the Helmholtz Centre for Georesearch. An earlier version incorrectly referred to a "reversal of the rotation direction of the Earth's core." The correct statement is that the Earth's inner core continues to rotate in the same direction as the Earth, but its speed fluctuates relative to the Earth's surface.
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