The Earth’s Rotation Is Gradually Slowing Down
The length of a day millions of years ago was shorter than today.
By Nathaniel ScharpingMarch 12, 2021 4:00 PM
If you could venture back in time to the Neoproterozoic era, about 620 million years ago, you’d notice a radically different planet. Most observable life forms would be alien-looking fronds and worms, and, if that didn’t send you running back to your time machine, you’d notice that even the days were different. Hundreds of millions of years ago, a day was only about 22 hours long, the result of a planet spinning about its axis more rapidly than it is now.
For billions of years, Earth’s rotation has been gradually slowing down. It’s a process that continues to this day, and estimates suggest that the length of a day currently increases by about 1.8 milliseconds every century. The day's length varies slightly from year to year, as well; the result of myriad forces both on and off Earth pushing and pulling at its rotation.
Scientists still don’t fully understand all the factors that contribute to changes in the Earth’s rotation. But the advent of extremely sensitive instruments for measuring data and keeping time have allowed them to track variations in our planet’s spin down to the microsecond. The effort has revealed that Earth’s rotation is in constant, microscopic flux. Each day is different than the last.
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