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Planet Earth

02
Oct

In 200 Million Years, Days Will Be 25 Hours Long

Wish you had another hour in the day to get everything done? Just wait 200 million years, when days here on Earth will stretch to 25 hours.

While we like to think of the Earth’s rotation as one of the few constants in this world, it’s anything but. For hundreds of millions of years, days have been growing longer and longer. The changes are small enough that our circadian clocks can’t detect them, but atomic clocks certainly can. According to the National Institute of Standards and Technology, which runs the United States’ atomic clocks, days today are longer than those a century ago by two milliseconds. Add that up over millions of years and you start to see real changes—days in the Jurassic period were only 23 hours long, for example.

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The Earth's rotation has slowed two milliseconds in the last century.

Two milliseconds over a century may seem inconsequential, and for most of human history it was. But with computers, GPS, and modern communications, even inaccuracies of a nanosecond can introduce unwanted error.

Ivan Amato, reporting for the Washington Post:

Consider GPS signals between satellites and receivers on the ground. Those are radio signals that move at the speed of light, which means they travel about one foot every billionth of a second (which is a nanosecond). So if the clocks in GPS satellites and your GPS receiver drift just one millionth of a second — a thousand nanoseconds — out of sync with each other, the system will not pinpoint your location more precisely than within about two-fifths of a mile. If the synchronization drifts off by one thousandth of a second, the system couldn’t tell you for sure if you were in Washington or Boston.

GPS isn’t the only system that’s dependent on highly-accurate timekeeping. Everything from the landing of the Mars rover Curiosity to you reading this article on the internet are coordinated on timescales measured in small fractions of a second.

So what’s slowing the Earth? The biggest drag is the moon, which raises and lowers the oceans and, less perceptibly, the Earth’s crust. Earthquakes, the Earth’s core, and even wind currents also play a role—anything that shifts the Earth’s mass. Some events speed up the rotation, but the overall trend is toward longer days. Keeping track of these changes may not seem all that important, but the next time you hop on a plane or even update your Facebook status, be thankful someone thinks its a big deal.