Day Length on Earth is Increasing
When Earth was formed 4.6 billion years ago, one day would have been roughly six hours long. By 620 million years ago, this had increased to 21.9 hours. Today, the average day is 24 hours long but is increasing by about 1.7 milliseconds every century.
The Moon’s Influence on Earth’s Rotation
The moon is slowing down Earth's rotation through the tides that it helps create. Earth's spin causes the position of its tidal ocean bulges to be pulled slightly ahead of the moon-Earth axis, which creates a twisting force that slows down Earth's rotation. As a result, the length of Earth's day is increasing and getting longer — but not long enough to make a difference to your busy schedule.
“The moon will continue to go farther away and Earth will continue to slow down,” Kurt Lambeck, a geophysicist at the Australian National University in Canberra says, until Earth becomes tidally locked, meaning only one hemisphere of our planet will see the moon in the sky. (As the moon is already tidally locked in its revolution around Earth, so we see the same lunar hemisphere at all times.) A single day on Earth could eventually exceed 1,000 hours, but a back-of-the-envelope reckoning has this happening in 50 billion years. By then, the oceans—the main source of tidal friction—will have long since evaporated, and Earth and the moon might be toast, gobbled up tens of billions of years earlier by the ballooning red giant sun.
