Earth’s day-night cycle, traditionally defined as a precise 24-hour period, is not as rigid as it seems. Due to the planet’s dynamic and complex nature—comprising a molten iron core, a fluid outer layer, and external influences like the Moon’s gravitational pull—variations in Earth’s rotation are a reality. These fluctuations, although tiny, are measurable over timescales ranging from decades to millennia and have intrigued scientists for years.
A team of geophysicists from ETH Zürich has made strides in understanding one of these enigmatic fluctuations. While some changes in Earth’s rotation are well-documented—such as a gradual lengthening of the day by 1.72 milliseconds per century due to the Moon’s effects—others are less clear. Decadal fluctuations of 2 to 3 milliseconds have been attributed to large-scale flows in Earth’s fluid core. However, a more mysterious fluctuation of 3 to 4 milliseconds, recurring approximately every thousand years, has defied clear explanation.
This recent study revisits the millennium-scale variation, linking it to activity at the core-mantle boundary. Advances in theoretical modeling and observational techniques allowed the researchers to build upon earlier efforts, which struggled to reconcile models with observational data. To isolate the core’s influence, the team meticulously accounted for other contributors to variations in Earth’s rotation, such as ice and water mass redistribution, crustal elasticity, and the Moon’s gravitational pull. What remained was a pattern consistent with fluid motion within Earth’s outer core, supporting a simplified magnetohydrodynamic model.
The study employed neural networks and magnetic field measurements from both ancient rock records and modern instruments. Historical data, including eclipse observations and lunar occultations dating back to 720 BCE, also played a pivotal role in reconstructing the history of Earth’s rotation. The findings suggest that shifts in Earth’s ice and water masses exert a smaller influence on rotational variability than previously believed.
Despite these breakthroughs, the research leaves room for further exploration. Identifying the subtle forces driving variations in Earth’s rotation is a daunting task, with significant margins of error due to the complexity of Earth’s internal and external dynamics. The authors emphasize the need for a more comprehensive physical model of core dynamics and a larger dataset to refine their understanding of these processes.
This research highlights the intricate relationship between Earth’s geodynamics and its rotational behavior. While significant progress has been made in deciphering the millennial-scale fluctuation, questions remain. The study underscores that variations in Earth’s rotation are not merely a curiosity but a window into the planet’s inner workings, shaped by fluid motions in the core, gravitational interactions, and the redistribution of mass across its surface.
By continuing to refine observational techniques and modeling approaches, scientists aim to uncover the full scope of influences that contribute to Earth’s rotational wobbles, enhancing our understanding of the planet’s dynamic systems.
https://www.sciencealert.com/something-in-earths-core-may-be-altering-the-length-of-days