LOS ANGELES — According to new research, Earth’s inner core, a massive iron sphere deep within our planet, has slowed its rotation. Scientists at the University of Southern California say their discovery challenges previous views about the behavior of the inner core and raises intriguing questions about its influence on Earth’s dynamics.
It has long been known that the inner core, a mysterious realm located nearly 5,000 kilometers beneath our feet, rotates independently of the Earth’s surface. Scientists have studied this phenomenon for decades, believing that it plays a crucial role in generating our planet’s magnetic field and shaping the convective patterns in its liquid outer core. Until now, it was generally accepted that the inner core gradually rotated 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 story.
“When I first saw the seismograms indicating this change, I was amazed,” John Vidale, Dean’s Professor of Earth Sciences at the USC Dornsife College of Letters, Arts and Sciences, said in a statement. “But when we found another 20 observations that signaled the same pattern, the result was inescapable. The inner core had slowed down for the first time in many decades. Other scientists have recently argued for similar and different models, but our latest study offers the most compelling solution.”
Slowed rotation, reversing rhythm
By analyzing seismic waves generated by repeated earthquakes in the South Sandwich Islands from 1991 to 2023, the researchers found that the rotation of the inner core had not only slowed, but actually decreased. reverse direction. The team focused on a specific type of seismic wave called PKIKP, which traverses the inner core and is recorded by seismic arrays in northern North America. By comparing the waveforms of these waves from 143 pairs of repeating earthquakes, they noticed a peculiar pattern.
Many of the earthquake pairs showed seismic waveforms that changed over time, but remarkably, they later reverted to their earlier counterparts. This observation suggests that after a period of superrotation from 2003 to 2008, the inner core began to subrotate, or spin more slowly than the Earth’s surface, essentially following its previous path. The researchers found that between 2008 and 2023, the inner core rotated two to three times slower than the previous superrotation.
The study’s findings paint a compelling picture of the rotational dynamics of the inner core. The corresponding waveforms observed in numerous earthquake pairs indicate moments when the inner core returned to positions it had occupied in the past, relative to the mantle. This pattern, combined with insights from previous studies, shows that the rotation of the inner core is much more complex than a simple, steady superrotation.
The researchers found that the inner core’s superrotation between 2003 and 2008 was faster than its subsequent subrotation, indicating an asymmetry in its behavior. This difference in rotation rates implies that the interactions between the inner core, outer core and mantle are more complicated than previously thought.
Limitations: Pieces of the core puzzle
Although the study provides compelling evidence for the decelerating and reversing rotation of the inner core, 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 hindered continuous core drilling. 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 call for continued refinement of Earth system models to better capture the complexity of the inner core’s behavior and its interactions with the outer core and mantle.
What do the findings mean for the future?
The discovery of the slowing and reversing 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 linked to the Earth’s magnetic field and the convection patterns in the outer core.
This study also raises fascinating questions about the possible consequences of the changing rotation of the inner core on the Earth’s surface. Could these variations in rotation affect Earth’s magnetic field, climate, or even the length of our days? Vidale suggests it’s possible the change could lead to changes in the length of a day by fractions of a second. “It’s very difficult to notice, on the order of a thousandth of a second, almost lost in the noise of the swirling oceans and atmosphere,” he says.
Future research will undoubtedly explore these intriguing possibilities further.
“The dance of the inner core may be even more alive than we know yet,” Vidale adds.
This article was reviewed by Steve Fink, editor-in-chief of StudyFinds.