A Gravitational Battle Within the Earth Is Changing the Length of Days

Scientists have already pinpointed a handful of compounding causes. Fluctuations in the atmosphere and oceans can slightly speed up or slow down the Earth’s rotation; major earthquakes can redistribute part of the planet’s mass; and by depositing enormous amounts of water into the oceans, melting continental ice is also a factor.

These influences account for some of the more sudden and recent changes, but on a several decades-long timescale, some of the variation appears to originate from a source much…