Astronomy
Gradual Slowing of Earth's Rotation and Day Length Increase
Quick fact
Fossil corals show that 370 million years ago, Earth had about 400 days per year, meaning each day was only about 22 hours long. The Moon is currently slowing Earth's rotation by about 1.8 milliseconds per century.
Why this is interesting
Earth takes 24 hours to spin once—but it hasn't always been that way. Billions of years ago, a day was only about 6 hours long. What has been putting the brakes on our planet?