Hidden Structure May Exist Inside Earth’s Core, Scientists Say

Scientists have identified evidence suggesting Earth’s inner core may contain a previously unknown layer, challenging long-standing models of the planet’s interior structure.

The findings come from a study led by researchers at The Australian National University (ANU), published in the Journal of Geophysical Research: Solid Earth. By analyzing seismic waves from earthquakes that travel through Earth’s interior, the team detected variations in wave behavior that indicate the inner core is not a uniform sphere but contains a distinct internal zone.

This potential inner layer, often referred to as the “innermost inner core,” lies within the solid inner core and may represent a separate phase in Earth’s geological evolution. The discovery suggests the planet’s center is more complex than the traditional four-layer model of crust, mantle, outer core, and inner core.

According to Joanne Stephenson, a PhD researcher at ANU and lead author of the study, the idea of an additional layer within the inner core has been proposed before, but earlier data lacked clarity. The new analysis used a search algorithm to compare thousands of inner core models with decades of seismic data collected by the International Seismological Centre, allowing researchers to identify which models best matched observed wave patterns.

The inner core, composed primarily of iron and nickel, reaches temperatures exceeding 5,000 degrees Celsius and accounts for about one percent of Earth’s volume. Despite its small size, it plays a key role in understanding the planet’s thermal history and magnetic field generation. Because direct observation is impossible, seismic wave analysis remains the primary method for studying its structure.

The study focused on seismic wave anisotropy—the way wave speeds vary depending on the direction they travel through the inner core’s material. Differences in how waves propagate through the inner core suggest variations in crystal alignment or material composition, which could indicate a layered structure rather than a homogeneous mass.

If confirmed, the existence of an innermost inner core would imply that Earth’s interior underwent a significant change in its early history, possibly related to shifts in the planet’s magnetic field or the crystallization process of the inner core over time. Such a discovery could require updates to geophysical models and educational materials describing Earth’s structure.

The research builds on earlier work from 2020 by the same ANU team, which first identified signs of complexity within the inner core. The latest analysis strengthens the case for a distinct internal layer by refining the interpretation of seismic data and eliminating alternative explanations for the observed wave behavior.

While the findings are based on indirect evidence, they highlight how advances in data analysis and modeling continue to reveal new details about inaccessible parts of Earth. Scientists emphasize that further studies using additional seismic events and improved modeling techniques will be needed to confirm the nature and properties of this potential inner layer.

As research into Earth’s deep interior progresses, discoveries like this underscore the dynamic and evolving nature of geophysical science, where even the most fundamental aspects of planetary structure remain open to revision based on new evidence.