For billions of years, the moon has been ever so gently tugging at the Earth and slowing down its rotation. Though many factors affect the planet’s rotation, by far the most important and long-lasting is our natural satellite, the moon. By comparing the time it takes for a signal to disappear and reappear, scientists can calculate with great precision how long it’s taken for the Earth to make a full rotation. As the Earth spins, these signals come in and out of view. It relies on space telescopes located far apart on Earth’s surface attuned to signals from outer space. Scientists today can measure even the smallest changes in the Earth’s rotation thanks to a technique known as Very Long Baseline Interferometry. Forces within the planet itself, like the movement of its core and winds on its surface, affect how Earth spins, as well as external processes like the gravitational pull of other bodies. But, once set in motion, that rotation is never constant. The way celestial bodies develop, by a gradual gravitational accretion of rocks and dust floating in space, results in a natural rotational movement. The Earth has been spinning like a top ever since it formed. The effort has revealed that Earth’s rotation is in constant, microscopic flux. 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. Scientists still don’t fully understand all the factors that contribute to changes in the Earth’s rotation. 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. 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. 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.įor billions of years, Earth’s rotation has been gradually slowing down. 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. If you could venture back in time to the Neoproterozoic era, about 620 million years ago, you’d notice a radically different planet.
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