Los Angeles – A new study suggests that Earth’s inner core — the solid ball of iron deep inside the planet — is spinning slower. University of Southern California scientists say the discovery challenges previous concepts about how the inner core behaves and raises intriguing questions about its impact on Earth’s dynamics.
It has long been known that the inner core, a mysterious region roughly 3,000 miles beneath our feet, rotates independently of the Earth’s surface. Scientists have studied this phenomenon for decades and believed it plays a key role in generating the Earth’s magnetic field and shaping the convection patterns in the liquid outer core. Until now, it was widely accepted that the inner core was gradually rotating faster than the rest of the Earth. This process is Super RotationBut this latest study, published in the journal Nature, It reveals the surprising twist in this story.
“When we first saw the seismic records suggesting this change, we were perplexed,” John Vidale, chair of the Department of Earth Sciences at the University of Southern California’s Doon Seif College of Arts and Sciences, said in a statement. “But when we found 24 more observations showing the same pattern, the result was inescapable: the inner core’s velocity had slowed for the first time in decades. Other scientists have recently argued for similar and different models, but our latest study presents the most compelling conclusion.”
Slow down the rotation and reverse the rhythm
By analyzing seismic waves generated by repeated earthquakes in the South Sandwich Islands between 1991 and 2023, the researchers found that not only has the rotation of the inner core slowed down, but it has actually Reverse directionThe team looked at a particular type of earthquake wave, called PKIKP, that traverses the inner core and is recorded by seismic arrays across northern North America. By comparing the waveforms of these waves from 143 pairs of repeating earthquakes, the team noticed a peculiar pattern.
Many of the earthquake pairs exhibited seismic waveforms that changed over time, but surprisingly later matched earlier waveforms. This observation suggests that after a period of superrotation from 2003 to 2008, the inner core began to subrotate, that is, rotate more slowly than the Earth’s surface, and essentially began to follow its previous orbit. The researchers found that from 2008 to 2023, the inner core subrotated two to three times slower than it had previously superrotated.
The findings of this study paint a fascinating picture of the rotation dynamics of the inner core. Coincident waveforms observed in numerous earthquake pairs show moments when the inner core returns to the position it previously occupied relative to the mantle. This pattern, combined with insights from previous studies, makes it clear that the rotation of the inner core is much more complex than a simple, stable superrotation.
The researchers found that the inner core’s super-rotation from 2003 to 2008 was faster than the subsequent sub-rotation, revealing 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.
Restrictions: Core puzzle pieces
While this study provides compelling evidence that the rotation of the inner core is slowing and reversing, it of course has limitations. The spatial coverage of seismic data is relatively sparse, especially in the North Atlantic, because the presence of chert layers prevents continuous coring. Moreover, the Earth system model used in this study, despite its sophistication, is only a simplified representation of complex dynamics.
The authors emphasize that further collection of higher-resolution data from a wider range of sites is needed to strengthen their findings, and they also call for continued refinement of Earth system models to better capture the complexities of the inner core’s behavior and its interactions with the outer core and mantle.
What do these findings mean for the future?
The discovery that the inner core’s rotation is slowing and reversing has huge implications for our understanding of the Earth’s interior and its impact on Earth’s dynamics. The behavior of the inner core is intimately linked to the Earth’s magnetic field and convection patterns in the outer core.
The study also raises intriguing questions about the potential impact of changes in the inner core’s rotation on the Earth’s surface. Could changes in rotation affect Earth’s magnetic field, climate, or even the length of the day? Vidal suggests that the change could result in a fraction of a second change in the length of the day. “Changes of a thousandth of a second would be barely noticeable above the noise of disturbances in the ocean and atmosphere,” he says.
Future studies will undoubtedly explore these intriguing possibilities in more depth.
“The inner core dance may be even more active than we previously knew,” Vidale added.
This article was reviewed by Steve Fink, Editor-in-Chief of StudyFinds.