Atomic clocks, combined with precise astronomical measurements, have revealed that the length of a day is suddenly getting longer.

This has critical impacts not just on our timekeeping, but also things like GPS and other technologies.

Over the past few decades, Earth's rotation around its axis has been speeding up.

But since 2020 that steady speedup has curiously switched to a slowdown and the reason is so far a mystery.

Over millions of years, Earth's rotation has been slowing down due to friction effects associated with the tides driven by the Moon.

For the past 20,000 years, another process has been working in the opposite direction, speeding up Earth's rotation.

When the last ice age ended, melting polar ice sheets reduced surface pressure, and Earth's mantle started steadily moving toward the poles.

Our planet's spin rate increases when this mass of mantle moves closer to Earth's axis.

Over decades and longer, the connection between Earth's interior and surface comes into play too.

Since the 1960s, we have had very precise estimates of Earth's rate of rotation.

A comparison between these estimates and an atomic clock has revealed an ever-shortening length of day over the past few years.

Scientists think it could be long-term tidal effects working in parallel with other periodic processes to produce a temporary change in Earth's rotation rate.