October 3, 2026
A recent study by two University of Alberta researchers shows that there is a hidden force deep within the Earth that can influence the speed of the planet’s rotation, causing a change in the length of the day on the order of milliseconds.
The two geophysicists, Huifeng Zhang and Matthew Demberry, based their research on an analysis of records extending between 1964 and 2019. The researchers combined seismic data used to track the rotation of the inner core, with models of the movement of the liquid outer core that were reconstructed based on changes in the Earth’s magnetic field.
The researchers sought to isolate the effects of other external and surface factors that affect the Earth’s rotation, such as winds, ocean movement, and the long-term influence of the Moon, before comparing the remaining changes in day length with three different mechanisms.
The results of the analysis showed that the gravitational interaction between the Earth’s inner core and the surrounding mantle is the most consistent explanation with the observed changes. The inner core consists of a very hot and dense ball made up mainly of iron and nickel, but it is not completely spherical. In addition, the distribution of mass in the mantle is heterogeneous. As the inner core rotates, the interaction of these unequal distributions creates what is known as “gravitational torque,” which has the ability to slightly accelerate or slow down the Earth’s rotation, thus changing the time it takes to complete a complete rotation around its axis.
The researchers linked this effect to a pattern of changes in the Earth’s rotation that extends for about 70 years, indicating that the inner core – despite its solidity – is capable of slowly changing its shape in response to the forces surrounding it. The calculations showed that the assumption of absolute rigidity of the inner core is not consistent with the observed changes, while the results become more consistent when the model is allowed to change its shape gradually, as estimates show that these changes occur over a period ranging between 8 and 10 years, within a possible range extending from two to 31 years.
The study also found indications of the possibility of the presence of an iron-rich, electrically conductive layer near the base of the mantle with a thickness of about two kilometers, in addition to accumulations of hotter materials that differ in their chemical composition. These are findings that researchers inferred through models and calculations without observing them directly.
In the same context, the researchers cautioned against asserting that the 70-year pattern represents a regular and certain cycle, as there is still ambiguity surrounding whether this pattern is repeated periodically over time or is merely a reflection of the special circumstances that prevailed during the period of seven decades included in the data.
