Earth’s rotation is slowing down, but it will never fully stop on its own. The planet loses about 1.4 milliseconds of day length every century due to the gravitational tug of the Moon. At that rate, billions of years would need to pass before rotation ceased, and the Sun will destroy Earth long before that happens.
How Scientists Measure the Change
Since the development of atomic clocks, scientists can track Earth’s rotation with extraordinary precision. The National Institute of Standards and Technology has documented that days grow longer by about 1.4 milliseconds per century on average. But the slowdown isn’t perfectly smooth. Some years, days actually get shorter by nearly 2 milliseconds, likely due to shifts in how mass is distributed inside the planet, changes in ocean currents, or interactions between Earth’s core and mantle.Earth’s rotation is slowing down, but it will never fully stop on its own. The planet loses about 1.4 milliseconds of day length every century due to the gravitational tug of the Moon. At that rate, billions of years would need to pass before rotation ceased, and the Sun will destroy Earth long before that happens.
Why Earth Is Slowing Down
The Moon’s gravity pulls on Earth’s oceans, creating tidal bulges on opposite sides of the planet. Because Earth spins faster than the Moon orbits, these bulges get dragged slightly ahead of the Moon’s position. That misalignment creates a small gravitational torque, like a brake pad pressing against a spinning wheel. The energy doesn’t disappear. It transfers to the Moon, pushing it into a wider orbit at a rate of about 3.8 centimeters per year.
This process, called tidal friction. We know this because fossil corals preserve daily growth rings, and ancient specimens tell a striking story. Corals from the Middle Devonian period, roughly 395 million years ago, show about 410 growth rings per year. That means a day lasted only about 21.5 hours, and the year was packed with far more sunrises than we experience now. Earth has been losing rotational energy steadily over geological time, and those ancient fossils are the receipts.
