Why Earth’s 24-hour day isn’t quite as fixed as you think
Sudden and recent changes are influenced by atmospheric and ocean fluctuations
Scientists have recorded minuscule, millisecond-scale variations in the length of Earth’s days over decades, indicating Earth’s days are no longer the same in length driven by shift in rotation speed.
Reasons abound. Some are known short-term causes and some are deep Earth influences responsible for changing the day's length.
Sudden and recent changes are influenced by atmospheric and ocean fluctuations, major earthquakes redistributing mass, and melting continental ice depositing water into the oceans.
Over decades, variations originate deep within the Earth, specifically from the constant motion of the ultra-hot liquid metal in the outer core, which alters the planet's rotation speed. But their transmission remains a mystery for the researchers due to weak friction between the core and mantle.
Because of it, geologists previously struggled to understand how these deep forces transmitted to the rest of the planet. A recent research study published in Nature took researchers one step closer to solving this enigma.
It proposes a "hidden gear" involving gravity: the gravity of the inner core pushes rotation in one direction and other interactions between the core and the mantle oppose it, resulting in small accelerations and decelerations over decades.
Mathieu Dumberry, a geophysicist at the University of Alberta involved in the study, said, “The idea is based on the fact that the inner core does not rotate at the same rate as the rest of the planet, causing it to become slightly misaligned with certain mass irregularities in the mantle. But the core wants to be aligned.”
Researchers reconstructed this gravitational interaction between 1964 and 2019 using seismic estimates and liquid metal flow models. However other factors could be involved in variability of day length but this study brings forth a major gravitational component behind this phenomenon.
