Earth’s Inner Core Has Been Slowing Down for Over a Decade

The Earth’s inner core has been slowing down since around 2010, subtly altering our days.

Key Takeaways

1. The Earth’s inner core has been slowing down for over a decade, moving slower than the surface.
2. Scientists confirm that this shift affects the length of a day by tiny fractions of a second.
3. Researchers analyzed seismic waves from earthquakes and nuclear tests to track the inner core’s movement.
4. The slowdown is influenced by the liquid outer core’s convection and gravitational forces in the mantle.
5. While this phenomenon is significant for geophysics, its effects on daily life remain imperceptible.

_____

Earth’s Inner Core Is Slowing Down, Changing Day Length by Fractions of a Second

The Earth’s inner core, a solid sphere of iron and nickel about 3,200 miles (5,150 km) below the surface, has been slowing down for more than a decade, according to a new study from the University of Southern California (USC). This change, while imperceptible to humans, slightly alters the length of a day by fractions of a second.

Scientists have long studied the movement of the inner core by analyzing seismic waves from earthquakes and nuclear tests. These waves travel through the planet’s layers and reveal how the inner core moves relative to the surface. In the new study, researchers examined seismic data from 121 repeating earthquakes near the South Sandwich Islands in the South Atlantic, recorded between 1991 and 2023, along with data from past nuclear tests. Since repeating earthquakes occur in the same location, their seismic waves should be nearly identical—but slight changes in their timing over decades indicate that the inner core’s rotation has shifted.

What’s Causing the Slowdown?

The study confirms that the inner core, which had been rotating slightly faster than the Earth’s surface, began slowing around 2010. It is now moving more slowly than the surface for the first time in decades, a phenomenon sometimes referred to as “backtracking.” This change is primarily driven by convection in the surrounding liquid outer core, which also sustains Earth’s magnetic field, and gravitational interactions with the mantle above it.

John Vidale, a professor of Earth Sciences at USC and co-author of the study, emphasized that other researchers have proposed similar or differing models, but the new findings provide the most convincing evidence yet. While this discovery offers critical insights into Earth’s deep interior, researchers note that the impact on daily life is minimal—people won’t notice any difference, as the effect on day length is too small to detect without precise scientific instruments.

Understanding the inner core’s movement is crucial for refining models of Earth’s internal structure and long-term geophysical processes. Scientists continue to analyze seismic data to monitor these changes and their broader implications for Earth’s magnetic field and overall dynamics.