The Earth has been mysteriously slowing down for 50 years - now scientists think they know why

Planet Earth has begin spinning at a slower rate, making the days longer, and scientists are struggling to understand why.

In general, there are processes to point to that have lengthened the Earth’s day from its approximately 86,400-second length.

Over millions of years, the planet’s rotation has been slowing down due to friction caused by the Moon. Every 100 years, around 2.3 milliseconds is added to the length of a day – billions of years ago, a day on Earth only lasted 19 hours.

Now, however, the Earth’s continual slowness is unprecedented and has gone on for the past 50 years and, overall, Earth’s spin has slowed by about 6 hours in the past 2740 years, according to a study published in the Proceedings of the Royal Society A in 2016.

“It is found that the rate of rotation departs from uniformity, such that the change in the length of the mean solar day (lod) increases at an average rate of +1.8 ms per century. This is significantly less than the rate predicted on the basis of tidal friction, which is +2.3 ms per century”, the researchers wrote.

The Earth reached its shortest day on 29 June 2022, but the general trend is that the days are lengthening – with no explanation readily available.

There are a few theories: weather systems melting the ice sheets could have an effect over the long-term, as at lower altitudes the planet is shrinking inwards. However, these have been decreasing at a consistent rate, so may not fit such a sudden change.

It is possible that fluctuations in the planet’s rotational speed known as the "Chandler wobble" – where small, irregular movement of Earth’s geographical poles across the surface of the globe – could be causing an impact.

Finally, processes in Earth’s inner or outer layers, oceans, tides, or even climate, may be causing it. Major earthquakes can also change the length of a day, but the amount is usually miniscule.