LOS ANGELES — Earth’s inner core, a solid iron ball nestled deep within our planet, has slowed its rotation, according to new research. Scientists from the University of Southern California say their discovery challenges previous ideas about the behavior of the inner core and raises interesting questions about its influence on Earth’s dynamics.
The inner core, a mysterious realm located nearly 3,000 miles below our feet, has long been known to rotate independently of the Earth’s surface. Scientists have spent decades studying this phenomenon, believing it plays a key role in creating our planet’s magnetic field and shaping convection patterns in the liquid outer core. Until now, it was generally accepted that the inner core gradually rotates faster than the rest of the Earth, a process known as super-rotation. However, this latest study, published in the journal Nature, reveals a surprising twist in this narrative.
“When I first saw the seismograms that indicated this change, I was stunned,” says John Vidale, dean’s professor of earth sciences in the USC Dornsife College of Letters, Arts and Sciences. “But when we found two dozen other observations signaling the same pattern, the result was inevitable. The inner core has slowed down for the first time in many decades. Other researchers have recently argued for similar and different models, but our latest study provides the most convincing solution.
Slowing down the rotation, reversing the rhythm
By analyzing seismic waves generated by repeated earthquakes in the South Sandwich Islands between 1991 and 2023, scientists found that the rotation of the inner core not only slowed, but actually reverse direction. The team focused on a specific type of seismic wave called PKIKP that travels through the inner core and is recorded by seismic fields in northern North America. By comparing the waveforms of these waves from 143 pairs of repeating earthquakes, they noticed a peculiar pattern.
Many pairs of earthquakes showed seismic patterns that changed over time, but remarkably, they later returned to match their earlier counterparts. This observation suggests that the inner core began to subrotate, or rotate more slowly than the Earth’s surface, after a period of superrotation between 2003 and 2008, essentially returning to its previous orbit. The researchers found that from 2008 to 2023, the inner core subrotated two to three times slower than its previous superrotation.
The study’s conclusions paint a fascinating picture of the rotational dynamics of the inner core. The matching patterns observed in numerous pairs of earthquakes indicate moments when the inner core returned to the positions it occupied in the past relative to the mantle. This pattern, combined with findings from previous studies, reveals that the rotation of the inner core is much more complex than the simple, stable superrotation.
The researchers found that the superrotation of the inner core from 2003 to 2008 was faster than its subsequent subrotation, suggesting an asymmetry in its behavior. This difference in rotation rates suggests that the interactions between the inner core, outer core, and mantle are more complex than previously thought.
Limitations: Pieces Of The Core Puzzle
While the study offers compelling evidence for the slowing and reversal of the inner core rotation, the study obviously has some limitations. The spatial coverage of the seismic data is relatively sparse, especially in the North Atlantic, due to the presence of chert layers that prevented continuous coring. Furthermore, the Earth system model used in the study, despite its sophistication, is still a simplified representation of the complex dynamics at play.
The authors emphasize the need for additional high-resolution data from a wider range of locations to strengthen their findings. They also require continuous refinement of Earth system models to better capture the complexities of the behavior of the inner core and its interactions with the outer core and mantle.
What do these findings mean for the future?
The discovery of the slowing and reversal of the rotation of the inner core has major implications for our understanding of the Earth’s interior and its impact on the dynamics of our planet. The behavior of the inner core is closely tied to the Earth’s magnetic field and convection patterns in the outer core.
This study also raises fascinating questions about the potential consequences of changing the rotation of the inner core on the Earth’s surface. Could these rotation changes affect Earth’s magnetic field, climate, or even the length of our days? Vidale suggests that it is possible that the change could lead to changes in the length of the day by fractions of a second. “It’s very hard to notice, on the order of thousandths of a second, almost lost in the noise of the swirling oceans and atmosphere,” he says.
Future research will undoubtedly explore these intriguing possibilities in greater depth.
“The dance of the inner core may be even more alive than we know yet,” adds Vidale.
This article was reviewed by StudyFinds Editor-in-Chief Steve Fink.