Gravitational tug-of-war inside Earth is changing the length of our days

Gravitational and other forces generated by the movement of Earth’s metallic core can explain millisecond-length fluctuations in the length of the 24-hour day over decades. Researchers modelled the impact of various possible internal forces arising from interactions among Earth’s inner and outer cores, and its rocky mantle, which can subtly affect the rate of the planet’s rotation. They found that one scenario, in which a gravitational twisting force generated by the inner core was dominant, best matched the historical record of changes in the length of Earth’s days.