Recent seismic data analysis has unveiled intriguing new insights into the rotational dynamics of Earth’s inner core. A study published in Nature suggests that since approximately 2010, the inner core has been rotating more slowly than the planet’s mantle and surface layers.
This research builds upon a controversial finding from the previous year, which proposed that the inner core might periodically reverse its rotation relative to the mantle. The new study not only lends support to this idea but also indicates that the most recent rotational shift is occurring at a slower pace than anticipated.
John Vidale, a geophysicist from the University of Southern California, explains that while the inner core maintains its absolute rotational direction, its relative motion appears to have changed. This phenomenon can be likened to vehicles traveling at different speeds on a highway, where relative motion creates an illusion of backward movement.
The study examined seismic waves from repeating earthquakes in the South Sandwich Islands, recorded by instruments in Alaska between 1991 and 2023. By comparing waveforms from these quakes, researchers identified matches that suggest the inner core reversed its relative rotation around 2008.
Interestingly, the study found that post-reversal, the inner core’s rotation rate in the new direction is less than half of its previous speed. Vidale hypothesizes that this slower movement might be due to the gravitational influence of the mantle on the inner core’s structure.
While this research aligns with the 70-year oscillation cycle proposed in earlier studies, it has not convinced all scientists in the field. Some researchers, like Lianxing Wen from Stony Brook University, maintain that changes in the inner core’s surface shape could explain the observed data without invoking independent rotation.
The scientific community remains divided, with some experts suggesting that the truth may lie somewhere between these contrasting viewpoints. Hrvoje Tkalčić from the Australian National University emphasizes the need for more data to reach a definitive conclusion.
As researchers continue to grapple with the challenges of studying Earth’s inaccessible interior, the coming years may provide crucial evidence. If the proposed oscillation model is correct, the inner core may soon enter a period of rapid rotation, offering an opportunity to further validate or refine current theories.
This ongoing research not only deepens our understanding of Earth’s internal dynamics but also highlights the complexity of studying our planet’s hidden layers. As scientists work to unravel these mysteries, each new discovery brings us closer to comprehending the intricate workings of our planet’s core.