Hints of Changes in the Earth’s Inner Core Rotation and Shape

News Desk, Biggani.org
June 4, 2025

There was a time when the Earth’s inner core seemed like a mysterious cave—one that humans would never reach, and never know what happens there. But an invisible change in 2010 cast a flash of light into that darkness. Deep within the Earth, 5,100 kilometers below the surface, an intensely hot metallic sphere—almost as hot as the sun, the Earth’s inner core—was spinning on its own. Suddenly, one day, the speed of that rotation changed.

This story begins in the South Sandwich Islands, a region that regularly experiences earthquakes. Between 1991 and 2023, a team of scientists from China and the United States analyzed the paths of seismic waves generated by these earthquakes. They closely studied these waves from two seismic stations: Eielson in Alaska, USA, and Yellowknife in Canada. For years, these waves had been traveling through the Earth’s core in a consistent pattern. But one day, they noticed—something in the timing seemed off.

The truth hidden behind this “irregularity” was revealed in the journal Nature Geoscience. The lead researcher, Professor John Emilio Vidale of the University of Southern California, explained that around 2010, the Earth’s inner core slowed its rotation. Previously, it had been spinning faster than the rest of the planet; now it was rotating relatively slower. Coupled with this was another strange phenomenon: the shape or structure of the core had become distorted.

The researchers say that, like X-rays, the way earthquake waves change speed and direction as they travel through the Earth’s various internal layers paints a picture of our planet’s depths. By analyzing these waves, it became clear that the inner core is not just changing its rotation, but also its structure. It’s almost like the fluctuations of a human heartbeat—if you understand the rhythm, you can perceive the internal state.

Vidale says, “The simplest explanation could be that the movement of the outer core drives the inner core. Over time, it rearranges the core in new ways. But exactly how this happens, we still don’t know.”

The inner core is made of solid iron and nickel. The temperature there is 5,200 degrees Celsius, and the pressure is greater than anything found in the deepest ocean trenches. Scientists cannot reach these depths, so seismic waves are their only window.

The research also uncovered another complex aspect—some seismic waves from certain earthquakes did not show any deviations in timing. This suggests the core may have stopped rotating at some point, or even begun spinning in the opposite direction. Whether this behavior is normal, or if it signals something new, remains uncertain.

But it’s not just rotation—researchers believe the inner core’s shape is changing as well. Changes in the structure of the outer core or the density of the mantle can cause shifts in pressure and size at the core. Scientists identify this as “viscous deformation.”

These changes may not directly affect people’s daily lives. But researchers say they could impact Earth’s magnetic field. Satellites, compasses, and even interplanetary missions could be influenced by these changes.

Future research may reveal where the outer core’s movement is greatest, or where the inner core is most flexible. It could even clarify the link between the Earth’s deep internal changes and sudden “jerks” or fluctuations in the magnetic field—events that occur only after many years.

This uncertain drama deep within the Earth is like a living story—where each earthquake is the start of a new chapter, and every seismic wave brings us a new message. Scientists are simply trying to read those messages, while we wait in anticipation of new and unknown discoveries.