Published: Wed, June 06, 2018
Research | By Jody Lindsey

Earth’s Days Are Getting Longer-Thanks to the Moon

Earth’s Days Are Getting Longer-Thanks to the Moon

A new study has revealed days are getting longer as the Earth's rotation slows. As the moon slowly drifts away from Earth, its influence on our planet's spin around its axis is waning, thereby making days last longer. Writing in Proceedings of the National Academy of Sciences, Stephen Meyers at the University of Wisconsin-Madison and Alberto Malinverno at Columbia University in NY calculate that over the past 1.4bn years the moon has drifted about 44,000km from Earth to a distance of 384,400km.

"As the moon moves away, the Earth is like a spinning figure skater who slows down as they stretch their arms out", explained Professor Stephen Meyers, professor of geoscience at the University of Wisconsin-Madison.

The Earth and Moon are displayed in this image. A new study has traced the relationship between Earth and the Moon back 1.4 billion years, and found that, all the way back then, a day was just over 18 hours. According to Meyers, his team had the ambition of using astrochronology to tell time in the distant past and to develop very ancient geological time scales. We know the Moon is 4.5 billion years old - but if we extrapolate back the current rate, the Moon would have been so close to Earth 1.5 billion years ago that it would have been ripped apart by the planet's gravitational forces.

These variations are collectively known as Milankovitch cycles and they determine where sunlight is distributed on Earth, which also means they determine Earth's climate rhythms. To pin down the frequency of the cycles in Earth's deep history, the scientists looked at copper and aluminium ratios linked to climate change in the 1.4bn-year-old Xiamaling marine sediment in northern China, and the 55 m-year-old Walvis ridge in the south Atlantic, and fed these into a model.

Known as Milankovitch cycles, the researchers analyzed the changes in the orbit, tilt, and wobble of the Earth over millions of years. For instance, the Moon is now moving away from Earth at a rate of 3.82 centimetres (1.5 inches) a year. This is how they were able to determine the length of the day, and also the distance between Earth and the moon, for various periods.

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But going back farther in time poses more problems. At some point in the far future, it will reach a stable distance when it will be visible only from one half of Earth, and never seen from the other.

Meyers and his team used astrochronology, or the statistical method that connects astronomical theories with geological observations, to reconstruct the solar system's ancient history. Next, they want to apply their method to other intervals of geologic time, added study co-author and Lamont Research Professor at Columbia, Alberto Malinverno in the statement.

We sometimes wish days were longer to fit our busy schedules.

The study's approach was previously vetted by a team at Lamont-Doherty that employed a rock formation in Arizona to assess Earth's orbital fluctuations from almost circular to more elliptical on a 405,000-year cycle. "We are looking at its pulsing rhythm, preserved in the rock and the history of life", Meyers said in the statement.

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