The Moon Is Making Every Day on Earth Longer Than the Last, Study Shows

So much for the 24-hour clock.

Scientists have bad news for anyone spent the work day staring at the clock and wishing the day would hurry up and end. The days, a new Proceedings of the National Academy of Science study states, are getting longer because the Earth is spinning more slowly every year. The moon is partly to blame for this phenomenon, the study authors write, and there’s no stopping its day-stretching effects.

According to the paper, this process has already lengthened Earth’s days considerably over the last couple billion years. About 1.4 billion years ago, one day on this planet was only about 18 hours and 40 minutes long. Now, it’s 23 hours, 56 minutes and 4 seconds long, according to NASA. On average, a single rotation of Earth — commonly known as a “day” — has gotten 1/75,000 seconds longer each year. This small difference, however, adds up over millions of years. The researchers behind the study say this gradually slowing spin is the effect of the Earth and the moon slowly moving farther and farther apart as the moon’s gravitational influence becomes smaller.

As the moon orbits Earth at a greater distance, one of Earth's rotations (one day) slows by 1/75,000 of a second each year.


The new study, co-authored by Stephen Meyers, Ph.D., a professor of geoscience at the University of Wisconsin-Madison, and Alberto Malinverno, Ph.D., a research professor at Columbia University’s Lamont-Doherty Earth Observatory, isn’t just about the moon. The researchers initially set out to find a way to accurately study the many phases that our planet has undergone since its beginning, both in terms of its geology and its place in the solar system. When you’re trying to study dates extending that far back, radiocarbon dating isn’t nearly precise enough to count on.

The team focused specifically on Milankovitch cycles — the changes in Earth’s orbit, tilt, and wobble that happen over thousands of years and are credited the long-term climate shifts that led to ice ages. Using a new computer model, they united records of Milankovitch cycles with geological records in an effort to reconstruct the cycles further back in time than scientists have ever been able to before. Their model, which used data on ocean tides from the geologic record, accounted for changes in the distance between the Earth and the moon. It led them to the conclusion that the moon’s gradual drift away from Earth is causing the planet’s rotation to slow, which in turn is steadily drawing out the length of our days.

Examining the model’s findings against a 1.4-billion-year-old section of the Xiamaling Formation from Beijing and a 55-million-year-old sample from Walvis Ridge in the southern Atlantic Ocean allowed them to test whether it really could extrapolate changes in the Earth’s orbit, tilt, and wobble. These geological samples confirmed its accuracy, revealing changes to the Earth’s prehistoric climate that matched up to the researchers’ predictions.

The model doesn’t just reveal the Earth’s past; it also predicts a disconcertingly different future: As The Guardian wrote on Monday, the increasingly distant moon will eventually reach a stable distance from the Earth, at which point it will stop running away and only be visible from one-half of our planet. At that point, the days will, mercifully, not get any longer. In the meantime, take solace in the fact that, although length of the Earth day is getting stretched out, it’s happening so slowly that by the time you die, each year on Earth will only be about one one-thousandth of a second longer.

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