Earth's Core Is Rotating

Deep beneath our feet lies a world within a world. The Earth's core consists of a liquid outer layer surrounding a solid, super-heated iron-nickel sphere. Because this solid inner core is floating within the liquid outer core, it is not locked into the same rotation as the rest of the planet. Scientists first confirmed this differential rotation in the 1990s by studying seismic waves from earthquakes. As these waves travel through the core and out the other side of the planet, their path and travel time are recorded. By comparing data from identical earthquake locations decades apart, researchers noticed the waves were traveling through slightly different parts of the inner core, providing direct evidence that it had moved.

This deep-Earth dance is more complex than a simple, steady spin. More recent evidence points to an oscillating pattern, where the inner core's rotation periodically accelerates and decelerates relative to the surface, possibly on a multi-decade cycle. This complex movement is likely driven by a tug-of-war between the electromagnetic forces generated in the liquid outer core and the gravitational pull of the dense structures in the mantle above. This distant motion has tangible effects, contributing to tiny, millisecond-scale variations in the length of our day and playing a crucial role in the dynamics of the geomagnetic field that shields us from harmful solar radiation.