Inge Lehmann's discovery of Earth's solid metal inner core in 1936 continues to astound scientists and pique their curiosity. The rotation speed and direction of this enigmatic core have been a subject of intense debate over the years. Recently, a growing body of evidence has suggested significant changes in the core's spin, but the exact nature and implications of these changes have remained unclear.

The challenge lies in the fact that Earth's deep interior is inaccessible for direct observation or sampling. To gain insights into the inner core's motion, researchers have relied on studying how seismic waves from large earthquakes behave when they pass through this region. Variations in the behavior of these waves have allowed scientists to measure shifts in the position and rotation of the inner core.

Dr. Lauren Waszek, a senior lecturer of physical sciences at James Cook University, explains that theories about differential rotation of the inner core were proposed in the 1970s and 1980s. However, it wasn't until the 1990s that seismological evidence was published to support these theories. Disagreements among researchers arose due to the scarcity of detailed observations and limited available data about the inner core.

Despite the contradictory findings, a promising model put forward in 2023 suggests that the inner core had previously rotated faster than the Earth itself but has since slowed down. In fact, the core's rotation initially matched Earth's spin before progressively decelerating and even moving backward in relation to the surrounding fluid layers. While caution was urged at the time to gather more data, a new study published in the journal Nature on June 12 provides compelling evidence supporting the 2023 hypothesis.

The research not only confirms the slowdown in the core's rotation but also affirms that this deceleration follows a distinct 70-year cycle. Dr. John Vidale, Dean's Professor of Earth Sciences at the University of Southern California's Dornsife College of Letters, Arts and Sciences, and a coauthor of the study, points out that these findings add weight to the notion that the core's rotation experiences periods of speeding up and slowing down over decades.

Understanding the intricacies of the inner core's rotational patterns is crucial for comprehending the dynamics of our planet and its geological processes. This new research brings scientists a step closer to unraveling the mysteries of Earth's deep interior and sheds light on a previously unrecognized cycle of rotation changes in the core. As scientists continue to explore this fascinating phenomenon, it promises to enhance our understanding of Earth's evolution and inform future studies in geophysics.