Earth’s inner core may be changing its rotation, nearly 3,000 miles beneath our feet. Using decades of earthquake recordings, scientists have found evidence that this solid sphere of iron may sometimes rotate faster or slower than the rest of the planet. Discover how seismic waves reveal Earth’s deepest structure, why repeated earthquakes provide such important clues, and what this subtle change could tell us about the magnetic field and Earth’s rotation. The surprising detail lies in what scientists can actually measure.