A study by researchers at the University of Alberta has shed new light on how Earth’s inner core influences the planet’s rotation. By analyzing observational records spanning roughly six decades, scientists found that interactions between Earth’s inner core and its outer layers can cause small changes in rotational speed.

Earth’s inner core is surrounded by a layer of liquid iron known as the outer core, with the mantle and crust above it. Because the inner core can rotate at a different rate from the rest of the planet, gravitational interactions between the layers can produce a torque that slightly speeds up or slows down Earth’s rotation.

The liquid outer core also plays an important role by creating magnetic and physical friction between the inner core and the mantle. That friction resists the gravitational interaction and helps prevent larger fluctuations in Earth’s rotational speed.

Scientists have long observed that the length of a day can vary by milliseconds because of factors including atmospheric and seasonal changes. The new analysis examined data from the 1970s through 2021 to identify the smaller rotational changes associated with processes occurring deep inside Earth.

Although the changes are extremely small, they matter for technologies that depend on highly precise measurements of time and Earth's position. GPS and other satellite-navigation systems rely on accurate information about the planet’s rotation, while telecommunications, financial systems and scientific instruments also depend on precisely synchronized clocks.

The findings could help scientists improve models of Earth’s rotational behavior and better predict small changes over time. More accurate predictions can also help keep atomic timekeeping systems aligned with the physical rotation of the planet, reducing discrepancies that can accumulate and eventually require corrections.