Researchers studying decades of earthquake data say they have found the first evidence that, in addition to spinning backward, Earth’s inner core in changing shape.

The Earth’s inner core is 3,000 miles below the surface and was thought to be a solid sphere held by gravity in the molten outer core. Recent studies show that the inner core’s rotation rate or shape can change over years or decades. This was found through variations in seismic waves from repeated earthquakes.

The surface of Earth's inner core appears to be dynamic, changing shape as it rotates, earthquake waves reveal.