Scientists have made a groundbreaking discovery in Earth’s geology by uncovering a fifth layer of the planet. The discovery was made by a team of researchers from the Australian National University who used seismic waves generated by earthquakes to study the deepest parts of Earth’s inner core. By measuring the speed at which the seismic waves penetrate and pass through the inner core, the team found evidence of a distinct layer inside the Earth known as the innermost inner core, which is a solid metallic ball that sits within the center of the inner core.

The study, which analyzed data from about 200 magnitude-6 and above earthquakes from the last decade, has been published in the journal Nature Communications. According to the researchers, probing the Earth’s center is critical for understanding planetary formation and evolution. Dr. Thanh-Son Phạm, from the ANU Research School of Earth Sciences, said, “The existence of an internal metallic ball within the inner core, the innermost inner core, was hypothesized about 20 years ago. We now provide another line of evidence to prove the hypothesis.”

Previously, four layers of Earth’s structure had been identified, including the crust, mantle, outer core, and inner core. However, the new findings indicate a fifth layer beneath that. The team studied the anisotropy of the iron-nickel alloy that makes up the Earth’s inner core. Anisotropy is used to describe how seismic waves speed up or slow down through the material of the Earth’s inner core, depending on the direction in which they travel.

The researchers found that bouncing seismic waves repeatedly probed spots near the Earth’s center from different angles. They analyzed the variation of travel times of seismic waves for different earthquakes and found that the crystallized structure within the inner core’s innermost region is likely different from the outer layer. The team suspects that there could have been a major global event at some point during Earth’s evolutionary timeline that led to a “significant” change in the crystal structure of the inner core. Overall, this discovery sheds new light on Earth’s complex and dynamic inner workings and opens up new avenues for further exploration and research.