Hidden Force Inside Earth Is Changing Length of Our Days, Study Finds

Scientists have identified a hidden force deep within the Earth that has been subtly altering the length of our days for decades. The phenomenon, driven by a gravitational tug between the planet's solid inner core and its rocky mantle, is causing shifts measured in thousandths of a second. While imperceptible to humans, these changes are significant enough to affect precise systems like GPS navigation and global timekeeping.

The findings, published in the journal Nature, are based on an analysis of records spanning from 1964 to 2019 by a team of physicists at the University of Alberta. Researchers combined data from earthquake waves and fluctuations in Earth's magnetic field to map movements within the planet's core.

This research suggests that Earth's solid inner core, a dense ball of iron and nickel, is not perfectly spherical. Its gravitational pull interacts with uneven concentrations of mass in the mantle, creating a 'gravitational torque' that influences the mantle's rotational speed. The study links these observed changes to a pattern that appears to span approximately 70 years, though it remains unclear if this cycle is reliably repeating.

Furthermore, the study indicates that the Earth's solid inner core can slowly change shape over several years. This flexibility is crucial, as calculations for a rigid inner core did not align with the observed shifts in day length. Allowing for deformation brought the predictions into closer agreement with the data.

To isolate the effects of the planet's interior, the researchers removed contributions from atmospheric winds, ocean movements, and longer-term processes like the moon's gravitational braking. They then compared three potential mechanisms against the remaining changes in day length. The gravitational mechanism, with other forces acting in opposition, provided the closest match.

The calculations also provided insights into the mantle's composition, suggesting the presence of an electrically conducting, iron-rich layer about 1.2 miles thick, and large accumulations of chemically distinct, warmer material. The findings also favor a specific type of mantle mineral that deforms relatively easily, which would help explain how deep-earth conditions influence the gravitational interaction.

The study authors cautioned that the apparent 70-year pattern should not yet be considered a confirmed, repeating cycle. They also noted that their conclusions rely on the accuracy of existing models for the inner core's rotation and liquid core flows, and that better models are needed to resolve remaining uncertainties. Nevertheless, the research demonstrates how subtle surface measurements can reveal crucial information about the dynamics, composition, and physical behavior of Earth's deep interior.