News > The gravitational interactions that have helped us dodge 60-hour days

The gravitational interactions that have helped us dodge 60-hour days

Earth has not always had 24-hour days. There were fewer than 10 hours in a day around 4.5 billion years ago, but they have grown longer as lunar tidal forces gradually slowed Earth’s rotation. Astrophysicists have now found that, from 2 billion to 600 million years ago, days were about 19.5 hours because several tidal forces cancelled each other out and kept Earth rotating at the same speed for over a billion years. If that had never happened, our present days might be over 65 hours long.