1.4 billion years ago, a day did not last 24 hours, but only 18. Our moon is moving away at a rate of about 3.8 centimeters per year, which is slowly but surely changing the length of our days on Earth.
For those who want the day to have more hours, a group of american geoscientists have good news for you: the days on earth are actually getting longer. This is because the moon is currently moving at a rate of 3.82 centimeters per year away from Earth. Stephen Meyers, Professor of Earth Sciences at the University of Wisconsin-Madison, illustrates this with the example of a spinning figure skater: “When she extends her arms, the rotation slows.”
In 1941, the engineer and astronomer Milutin Milankovich had already begun to elaborate calculations on the matter by accounting for the alternation of glacial and interglacial cycles during the Quaternary period. According to three parameters (eccentricity, obliquity and precision), he was able to establish so-called “Milankovitch cycles” that explain the natural climatic changes on Earth.
The american scientists were inspired by this theory and added to it the oscillation measurements of the Earth. They also measured the proportion of copper and aluminum in Chinese marine sediments and in the Southern Walvis Ridge, south of the Atlantic, to perform their calculations.
“We were interested in reconstructing the Milankovitch cycles because they provide a powerful tool for evaluating the history of our planet, and the solar system. They are like signposts on a trail, allowing us to navigate geological history,” said Meyers.
The speed at which the moon is moving away used to be slower in the past. If we counted back the 3.82 centimeters per year continuously, the moon would have been so close to the earth 1.5 billion years ago that the gravitational force of the Earth would have torn it apart.
Meyers and colleagues were able to reconstruct how the distance of the moon has changed over time. One of the results: 1.4 billion years ago, an Earth’s Day lasted only 18 hours, because the proximity of the Moon increased the Earth’s self-rotation as the Sun orbit.