A July 2025 Nature Geoscience study by Peking University and USC researchers confirms the inner core stopped and began rotating opposite to Earth’s surface after slowing since 2009. Analysis of seismic waves from 1990 to 2021 revealed subtle changes in wave speed and trajectory that pinpoint the reversal of the solid iron-nickel core. The reversal marks the start of a roughly 60–70-year oscillation cycle first hypothesized after a 1970s directional shift. Scientists are evaluating how the new rotation phase may alter the geodynamo and modify the strength and structure of Earth’s magnetic field. Researchers warn that millisecond-scale variations in day length driven by core oscillations could have cumulative effects on long-term climate patterns.
