A groundbreaking study conducted by scientists at the University of Southern California (USC) has shed new light on the Earth’s inner core, revealing unexpected changes near its surface. Published in Nature Geoscience, the research suggests that the structure of the Earth’s inner core may be undergoing significant transformations, challenging long-held scientific beliefs about the nature of the planet’s innermost layer.
The Mystery of the Inner Core
The Earth’s inner core, located approximately 3,000 miles beneath the surface, has long been a subject of scientific intrigue and debate. For years, it was believed to be a solid sphere composed mostly of iron and nickel, surrounded by a molten outer core. This solid structure was thought to be stable, with little to no significant changes occurring over time. However, the findings from the USC team suggest that the dynamics of the inner core may be far more complex than previously imagined.
While the notion of rotational changes in the inner core had been previously explored, the focus of most research had been on the way the core rotates relative to the Earth’s surface. The USC scientists, however, were not initially set out to probe structural changes in the inner core. Their primary objective was to explore the phenomenon of the inner core’s slowing rotation.
As John Vidale, the lead author of the study and Dean’s Professor of Earth Sciences at USC, explained, the team’s discovery was unintentional but profound. “We didn’t set out to define the physical nature of the inner core. What we ended up discovering is evidence that the near surface of Earth’s inner core undergoes structural change,” Vidale said. This unexpected finding offers valuable insights into the processes driving the subtle changes in the Earth’s day length and could also explain some of the broader, ongoing shifts in the inner core’s behavior.
Seismic Waves: A Window into the Core
The USC scientists used seismic waveform data from earthquakes recorded over a span of several decades to gather their findings. They analyzed 121 repeating earthquakes from 42 locations near Antarctica’s South Sandwich Islands that occurred between 1991 and 2024. This dataset allowed them to study the seismic waves that travel through the Earth’s core, offering a glimpse into what is happening deep below the surface.
One particular dataset, collected from a receiver-array station near Yellowknife, Canada, stood out to the researchers. The seismic waves from this station exhibited unusual properties that were not seen in the other data sets. Initially, these anomalies confused the team. “At first, the dataset confounded me,” Vidale recalled. However, after further refinement of their resolution techniques, it became clear that these seismic waveforms revealed unexpected physical activity within the inner core itself.
The seismic waves suggested that there were structural changes occurring at the surface of the inner core, particularly near its boundary with the outer core. These waves seemed to indicate that the inner core was not static but rather underwent temporal deformations—that is, changes in shape over time.
Viscous Deformation of the Inner Core
The team’s analysis suggests that the near surface of the inner core may be experiencing viscous deformation, which means that it may be slowly changing shape over time. This deformation is likely caused by interaction between the inner and outer core. The molten outer core, which is composed of liquid iron and nickel, is known to be highly turbulent. The USC team’s findings indicate that this turbulence may be having a more significant impact on the inner core than scientists had previously realized.
Historically, the outer core’s turbulence was thought to have minimal effect on the solid inner core, particularly on human timescales. However, this new study presents compelling evidence that the dynamics of the outer core are actively disturbing the inner core, leading to changes in its shape.
Vidale explained, “The molten outer core is widely known to be turbulent, but its turbulence had not been observed to disrupt its neighbor, the inner core, on a human timescale. What we’re observing in this study for the first time is likely the outer core disturbing the inner core.” This insight is groundbreaking, as it suggests that the interaction between the two cores is more dynamic and complex than previously understood.
The Role of Topography and Earth’s Rotation
The study’s findings could help scientists better understand the broader implications of inner core dynamics. One of the most intriguing aspects of the research is how these structural changes could affect the Earth’s rotation. It is widely known that the inner core’s rotation is not perfectly synchronized with the rotation of the Earth’s surface. In fact, studies have shown that the length of a day has gradually been changing over time.
The new research from USC suggests that the structural changes at the inner core’s surface might be playing a role in these subtle shifts in the Earth’s rotation. As the inner core’s shape changes, it could cause minute alterations in the planet’s overall rotation, contributing to the gradual slowing of the Earth’s day. This insight could lead to a deeper understanding of the Earth’s long-term rotational behavior, shedding light on the forces that influence the planet’s movement.
Unveiling Hidden Dynamics of the Earth’s Core
Vidale’s team believes that this discovery opens up a new avenue for research into the dynamics of the Earth’s core. By examining the relationship between the inner and outer core, scientists may gain a better understanding of the complex processes that govern the planet’s interior. Furthermore, these findings could have broader implications for our understanding of the Earth’s thermal structure and the planet’s magnetic field.
The interaction between the inner and outer core is central to the generation of the Earth’s magnetic field. The outer core’s fluid motion creates electric currents, which, in turn, generate the magnetic field that surrounds the planet. If the turbulence in the outer core is disturbing the inner core, it could provide new insights into how the magnetic field is maintained and how it might change over time.
Moreover, understanding the dynamics of the core could help scientists make better predictions about future changes in the Earth’s magnetic field and its potential impacts on technology, navigation, and even climate.
The Path Forward
While this discovery represents a major leap forward in our understanding of the Earth’s inner core, much work remains to be done. Vidale and his team have laid the groundwork for further research into the interactions between the core layers, and they hope that future studies will provide more detailed insights into how these changes might affect the Earth’s geology and atmosphere.
The next steps for scientists will likely involve gathering more seismic data from different regions of the planet to better understand the temporal deformations in the inner core. Additionally, researchers will continue to refine their models of how the outer core’s turbulence might affect the solid inner core and its behavior.
By deepening our understanding of the Earth’s inner core, scientists are not only unlocking new mysteries about our planet’s interior but also paving the way for future discoveries that could have far-reaching implications for the fields of geophysics, climatology, and planetary science.
Conclusion
The new study by USC scientists represents a significant milestone in our understanding of the Earth’s inner core. By revealing evidence of structural changes at the core’s surface, the researchers have opened a new chapter in the study of the planet’s deep interior. These findings challenge long-standing assumptions and highlight the dynamic nature of the Earth’s core, with potential implications for our understanding of the Earth’s rotation, magnetic field, and even its geological history. As scientists continue to probe the mysteries of the inner core, this research will undoubtedly lead to new insights into the forces shaping the Earth’s interior and, ultimately, its evolution as a whole.
Reference: John Vidale, Annual-scale variability in both the rotation rate and near surface of Earth’s inner core, Nature Geoscience (2025). DOI: 10.1038/s41561-025-01642-2. www.nature.com/articles/s41561-025-01642-2