The duration of Earth’s days is not constant. For decades, scientists have documented minor fluctuations in rotation speed, often measuring in mere milliseconds. While these shifts are negligible to human perception, they signal significant changes in how the planet spins. Although atmospheric shifts, oceanic movements, major seismic events, and melting ice sheets are known contributors, a new study identifies a deeper mechanism responsible for variations occurring over several decades.
Published in Nature this week, the research proposes that a gravitational tug-of-war within the Earth’s interior is altering the length of days. Beneath the rocky mantle lies a 1,400-mile-thick layer of superheated liquid metal in the outer core. As these metallic flows fluctuate, they interact with the solid inner core, subtly influencing the rotation of the crust above.
Researchers have long struggled to explain how forces transfer between the core and mantle, as friction alone is too weak to account for observed changes. The new model suggests that because the inner core rotates at a different rate than the rest of the planet, it becomes slightly misaligned with mass irregularities in the mantle. Mathieu Dumberry, a geophysicist at the University of Alberta and co-author of the study, noted that the core naturally seeks alignment, causing gravity to pull the inner layers back toward a more harmonious position. This gravitational adjustment minutely affects surface rotation.
To test this theory, the team reconstructed Earth’s spin dynamics between 1964 and 2019 using seismic data on inner core rotation and models of liquid metal currents. The resulting gravitational model accurately reproduced both the timing and magnitude of observed rotational changes. While other unknown factors likely play a role, the authors conclude that gravity remains the dominant force in this internal competition, effectively winning the struggle and driving the gradual acceleration and deceleration of Earth’s spin.
Milliseconds matter for GPS and atomic clocks. Interesting how the planet’s heartbeat isn’t as steady as we thought.
Seems plausible, but are we sure this isn’t just a correlation? I’d like to see independent validation.
Wait, so gravity is pulling the core to match the mantle? That explains decades of unexplained rotation quirks!
Mind blown. I never realized the ground beneath our feet was actively fighting for alignment deep underground.