科学家数十年来记录到地球自转存在微小的毫秒级变化，显示地球自转速度正在改变。除了大气与海洋波动、大地震造成的质量重分配，以及大陆冰层融化等因素会引起自转突变外，数十年的长期变化则源于地表深处外核超高温液态金属的流动。

发表在《自然》期刊的一项新研究揭示了这种力的传递机制。由于内核与地函之间的摩擦力过于微弱，研究人员指出地核与地函并非完全同速旋转，导致内核与地函内部的质量分布出现偏差，而内核的重力会试图将这些层次拉回平衡位置。

研究人员结合地震观测数据与外核液态金属流动模型，成功重构了1964年至2019年间地球自转的变化历程。该模型高度重现了数十年间自转速度的时间点与变动幅度，证实了重力在内核与地函的交互拉锯中扮演主导角色，解开了地球自转周期波动的重要谜团。

For decades, scientists have recorded minuscule, millisecond-level variations in Earth's rotation, pointing to shifting rotational speeds. Beyond surface factors like atmospheric and oceanic fluctuations, major earthquakes, and melting continental ice that cause sudden shifts, decade-long variations stem from deep within the Earth, driven by the constant motion of hot liquid metal in the outer core.

A recent study published in Nature proposes a mechanism explaining how these deep forces are transmitted, as core-mantle friction alone is too weak. Because the inner core rotates at a different rate than the rest of the planet, it becomes misaligned with mantle mass irregularities, prompting the inner core's gravitational pull to tug Earth's interior layers back into harmonic alignment.

Using seismic rotation estimates and outer-core fluid flow models from 1964 to 2019, the researchers accurately reproduced both the timing and magnitude of observed gradual rotational changes. This demonstrates that despite complex competing forces, gravitational interactions between the inner core and mantle play a dominant role in driving decade-scale variations in Earth's spin.