Scientists have uncovered new evidence suggesting that Earth’s solid inner core may be changing shape. Seismic wave measurements from the past few decades point to significant changes in the structure of the core, leading to new questions about the planet’s deepest layer.
Evidence of Movement in the Inner Core
For years, researchers have known that Earth’s solid inner core is not entirely stationary. It appears to spin at a different rate compared to the rest of the planet. This change in rotation has been linked to the magnetic forces generated by the planet’s liquid outer core. As these forces continually act on the inner core, they create a shifting effect on its shape and structure.
John Vidale, a seismologist at the University of Southern California, explained that the magnetic forces from the liquid core constantly exert torque on the inner core, making it spin at different rates over time. This shifting is not just limited to the core’s rotation, but it also seems to involve changes in the core’s shape.
Seismic Waves Reveal Inner Core Changes
In a study published in Nature Geoscience, Vidale and his team analysed seismic waves from earthquakes occurring between 1991 and 2023. These waves, which travel through Earth’s interior, provided crucial data for identifying variations in the inner core. Researchers compared waves from earthquakes that occurred in the South Sandwich Islands, a region known for seismic activity.
Figure 2: Vidale and team analysed seismic waves from earthquakes (1991-2023) to identify variations in Earth’s inner core
The team identified over 160 pairs of seismic waves that passed through the same area of the inner core, but years apart. Interestingly, the seismic signals from waves that did not intersect with the inner core were nearly identical, suggesting little to no change in those areas. However, for those waves that intersected with the inner core, the signals showed differences, indicating that something within the core had changed. This discrepancy suggests that both the rotation and shape of the inner core have shifted.
Magnetic Forces at Play
Vidale and his colleagues suggest that the changes in shape could be caused by magnetic forces at the boundary of the inner and outer core. These forces may cause the solid inner core to deform or reshape over time, as convection currents within the outer core pull on the less viscous outer boundary of the inner core. The team also speculated that interactions between the inner core and the lower mantle could contribute to these changes.
Hrvoje Tkalčić, a geophysicist at the Australian National University, expressed his views on the new study, calling it a “step forward” in understanding the inner core’s dynamics. Tkalčić stated that the results of the study are promising but cautioned that shape changes might not be the only cause of the observed seismic wave differences.
Inner Core’s Structure: A Dynamic Landscape
The discovery of shape-shifting in Earth’s inner core adds a new layer of complexity to the planet’s internal dynamics. Vidale and his colleagues suggest that the inner core is not a static sphere. Instead, it may experience subtle but significant shifts, with some regions rising and falling by up to one kilometre within a few years. These movements could be likened to the shifting of mountains or landslides, though on a much larger scale and deep within the planet.
Severine Rosat, a geophysicist at CNRS, expressed her surprise at how the researchers managed to detect these small, yet significant, changes. She called the findings “encouraging” for other seismologists working in this field.
Uncertainty in the Causes
Despite the promising findings, the exact cause of these shape changes remains unclear. The changes could be a result of melting and freezing materials at the boundary of the inner and outer core, creating new structures over time. Alternatively, gravitational forces from the mantle could be pulling on the inner core’s surface, causing deformation.
Vidale, however, pointed out that these changes are not unprecedented. He suggested that volcanic-like activity, such as eruptions of molten iron from the inner core, could also explain some of the seismic discrepancies. These “burps” of material could lead to the deformations observed in the seismic data.
The Need for Further Research
As researchers continue to study the behaviour of the inner core, further data is necessary to confirm the causes of the observed changes. Vidale and his team have called for more studies and repeat earthquake data in the future to gain a deeper understanding of the inner core’s dynamic nature.
Tkalčić added that gathering more seismological data from remote areas, such as the ocean floor, would provide valuable insights into the evolution of Earth’s inner core. Such data would be essential in resolving the ongoing debate about whether the changes in seismic waves are due to changes in the core’s rotation, shape, or both.
Also read: US Tariff Exemption for Australian Metal Exports Under Consideration
Lianxing Wen, a seismologist at Stony Brook University, also weighed in on the discussion. While he acknowledged the new findings, Wen believed that the observed changes in shape alone could explain the seismic data, without needing to invoke changes in the rotation of the inner core.
Conclusion: A More Dynamic Inner Core
The discovery of shape-shifting in Earth’s inner core represents a significant step in understanding the complexities of our planet’s deepest layer. As researchers continue to gather data, it seems clear that the inner core is far more dynamic than previously thought. The study opens up new possibilities for understanding the processes that govern the planet’s interior, and further research will be crucial in uncovering the full scope of these changes.
