If you thought time flies way too fast these days, you're not technically wrong. On June 29, Earth experienced the shortest day ever since record-keeping with high-precision atomic clocks began, clocking in a full revolution around its axis 1.59 milliseconds short of 24 hours.
The days on Earth are supposed to get increasingly longer as time passes due to exchanges in angular momentums between Earth and the Moon. When life on the planet first emerged, about 3.5 billion years ago, a day lasted 12 hours. At the emergence of photosynthesis 2.5 billion years ago, the day lasted 18 hours. And 1.7 billion years ago when the first eukaryotic cells emerged, a day lasted 21 hours long.
While Earth's rotation speed is on a decreasing trend, the past few decades have been an anomaly with the planet's spin going against the grain and actually turning faster.
In 2020, scientists registered 28 of the shortest days in the past 50 years, with the shortest of those, on 19 July, shaving 1.47 milliseconds off the 86,400 seconds that make up 24 hours. The new 29 June record is just a few milliseconds shorter, but it still counts.
It's not entirely clear why days are getting shorter rather than longer as they have across geological history, but there are many factors that can have an influence. Strong winds during El Nino can slightly slow down the planet's rotation due to drag from the atmosphere, while earthquakes can have the opposite effect shortening days.
But what may explain the current temporary day shortening are wobbles in Earth's axis due to the fact that Earth is not exactly a perfect sphere. Earth has a bulge at the equator and its poles are slightly squashed. Any spinning sphere-like object that is not entirely spherical will wobble in some way.
According to scientists Leonid Zotov, Christian Bizouard, and Nikolay Sidorenkov, an irregular pattern of movements of Earth's geographical poles known as the 'Chandler Wobble' is particularly important. This wobble varies in amplitude from decade to decade, a motion that is thought to be driven by changes in pressure at the bottom of the oceans caused by fluctuations in salinity, temperature, and ocean circulation.
The Chandler Wobble, which has a period of 433 days and was discovered by American astronomer Seth Carlo Chandler in 1891, typically has a normal amplitude of 3 to 4 meters at Earth's surface. But Zotov says that from 2017 to 2020 the wobble disappeared, which may be explained by the melting and refreezing of ice caps on the world's tallest mountains.
Although variations in the length of day are imperceptible, they can add up over the years to produce significant effects. In fact, shorter or longer days than we're used to could make a mess out of our sensitive hardware whose clocks cannot always be synchronized by satellites. This has caused some concerns that echo the Y2K crisis, a problem in the coding of computerized systems that was projected to create havoc in computers and computer networks around the world at the beginning of the year 2000. But Y2K turned out to be no more than a minor nuisance and there are good reasons to believe changes in Earth's spin will not significantly affect time keeping during our lifetimes.
The International Telecommunication Union, a United Nations body, first added a leap second in 1972 in order to compensate for changes in the length of day and most recently added another one in 2016. However, scientists claim there's a good 70% chance the planet has reached its peak rotational speed, meaning we will most likely never experience a shorter day than on June 29. Sounds like the fast times are over.