Earth's Core May Change Day Length
Tuesday, October 6, 2026178 words3 minutes1961 reads
We use 24 hours as the length of a day, but Earth's rotation is not perfectly steady. On long time scales, the change can be a few milliseconds. The new research looks at broad changes that last many decades.
Earth has several layers. The mantle is a rocky layer about 3,000 kilometres thick that includes the crust. Far below it are a liquid outer core and a solid inner core. The core and mantle can exchange angular momentum, a property of moving, turning objects. When one part changes speed, another part can make a small opposite adjustment.
The researchers studied how the inner core moves compared with the mantle. The inner core is not a perfect sphere. Its shape and the uneven mass in the mantle can create a weak gravitational torque, or turning force. Their model suggests that this torque is the main driver of multidecadal day-length changes from 1964 to 2019. Electromagnetic and topographic forces at the core-mantle boundary may resist the change. The result is a possible explanation, not a direct view of Earth's center.
