Scientists Baffled to Find Signs of Another Core Within Earth’s Inner Core, Say ‘We Have to Rewrite the Textbooks’

For decades, schoolbooks have painted a relatively simple picture of Earth’s inner workings—a hard crust, a thick mantle, a swooshing liquid outer core, and a solid inner core at the center. But beneath that simple diagram lies a way more complicated and mysterious story—one that scientists are only now beginning to understand. Using seismic waves from earthquakes as a kind of X-ray vision, geophysicists have been listening to the mighty yet subtle echoes passing through the Earth’s deepest layers. In a stunning discovery, experts from the Australian National University (ANU) have found signs of a previously unknown structure hidden deep inside Earth’s core, stated AGU.

The discovery suggests that the solid Earth's inner core itself may contain an even more inner core, which scientists are now calling the "innermost inner core." It is a revelation that could rewrite humans’ whole understanding of the planet’s formation, cooling history, and the forces molding its magnetic field. In 2021, Australian National University (ANU) geophysicist Joanne Stephenson explained, "Traditionally we've been taught the Earth has four main layers: the crust, the mantle, the outer core and the inner core…It's very exciting – and might mean we have to re-write the textbooks!" as per ANU.

Stephenson and her team looked closely at how seismic waves, generated by earthquakes, travel through the Earth. It turns out these waves move at slightly different speeds depending on the structure and composition of the material they pass through. The team noticed subtle but consistent shifts in wave direction and speed that pointed to a particular region within the inner core, one that does not behave like the other layers around it. One prominent observation was the shift in the "slow direction" of the seismic waves to a 54-degree angle, with the faster direction aligned parallel to Earth’s rotational axis, stated Science Alert.

Stephenson remarked, "We found evidence that may indicate a change in the structure of iron, which suggests perhaps two separate cooling events in Earth's history…The details of this big event are still a bit of a mystery, but we've added another piece of the puzzle when it comes to our knowledge of the Earth's inner core."

But the story does not end there. In another stunning discovery, experts at ANU identified a strange doughnut-shaped structure buried almost 3,000 kilometers below the surface. This finding came from a different seismic approach—one that analyzed the echoes of waves for hours after earthquakes rather than just minutes. Professor Hrvoje Tkalčić, a co-author of the study, explained that this structure was hidden for a long time because old studies collected data with less 'volumetric coverage of the outer core,' stated Forbes.

This discovered zone, which lies somewhere between the liquid core and the mantle, is not a shell-like layer like the ones above it. Instead, it wraps around the Earth in a doughnut shape along the equatorial plane. These elements could be fueling powerful convection currents that generate the geomagnetic field—a protective force essential to life on Earth. Tkalčić remarked, "The region sits parallel to the equatorial plane, is confined to the low latitudes, and has a doughnut shape. We don't know the exact thickness of the doughnut, but we inferred that it reaches a few hundred kilometers beneath the core-mantle boundary."