Although most people consider a day to be a fixed period of 24 hours, Earth’s rotation speed can vary; these differences are measured in milliseconds. Changes in the length of the day are linked to movements in the core. Scientists have known for about 30 years that the liquid outer core can speed up and slow down, as shown by changes in the magnetic field. When the core speeds up, the mantle slows down, and when it slows down, the mantle speeds up; this exchange is explained by the conservation of total angular momentum. In a study published in Nature, Huifeng Zhang and Prof. Mathieu Dumberry of the University of Alberta determined that changes in the rotation of the inner core generate “gravitational torque.” This interaction affects the speed of the mantle. Torque at the core-mantle boundary limits the change through friction and electromagnetic resistance. The findings show that the inner core can change shape over periods of approximately 10 years.
Why it matters
The significance of the study lies in showing that the measurement of time, considered fixed in everyday life, can be affected by physical processes deep within the planet. Although millisecond differences cannot be directly felt, they provide a measurable link for scientific models that examine Earth’s rotation and internal structure together. Addressing changes in the shape of the inner core and the mechanisms at the core-mantle boundary within the same framework helps explain the source of the rotational variations observed at the surface. While the findings show that the relationship between changes in the magnetic field and the length of the day cannot be explained solely by surface conditions, they leave open the question of to what extent the effects of these interactions can be distinguished across different periods.
Background
Earth is not a new name in the FikirPilot archive: over the past 90 days, we have published 10 news reports mentioning this name; the most recent is dated September 29, 2026.