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A Day on Earth Used to Only Be 19 Hours

The Moon formed when a Mars-sized object slammed into the Earth billions of years ago. As the Moon orbited around the Earth, its tidal interactions carried it slowly away from the planet, slowing down Earth's rotation. For about a billion years, a day on Earth lasted 19 hours before it continued to slow down to the current 24-hour day. Geologists have developed a new technique for measuring the length of Earth's day using sedimentary layers that change over long periods following the Earth's orbit and rotation.

https://phys.org/news/2023-06-billion-