Earth’s inner core appears to have stopped spinning faster than its mantle. New measurements suggest that the rotation of the inner core has slowed in recent decades and is now about to reverse direction, spinning more slowly than the mantle. The finding helps to explain recent changes in Earth’s magnetic field and the length of day.
The Earth’s solid inner core is contained within the liquid outer core, enabling it to rotate differently from the Earth itself. Its spin is driven by the magnetic field generated in the outer core, and balanced by gravitational effects within Earth’s mantle.
By analysing earthquake seismic waves that have passed through the inner core, researchers were able to calculate how the spin of the inner core has changed since the 1960s. They found that seismic waves have tended to follow a very similar path since about 2009, suggesting that the inner core rotation has paused. The data showed something similar occurred in the early 1970s, indicating that the inner core appears to change in a similar way every few decades.
The new finding, which is published in Nature Geoscience, is helping scientists to better understand the interaction between different layers of the Earth, and the impact that processes deep inside the Earth can have on the surface, including the gradual increase in length of day: adding a fraction of a millisecond each year since 2020.
