Here's Why Earth Almost Ended Up with a 60-Hour Day
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Since the Moon's influence has been much stronger than the Sun's for most of Earth's history, the slowdown has dominated. But there was the aforementioned period during which the days stayed steady. The team found this because of the atmosphere: It was warmer and, therefore, bigger.
But a property called resonance also played a role. This is when waves travel through the atmosphere at a particular height and speed to produce a synchronization. The velocity of these waves is partially determined by temperature.
During this stable period in Earth's day-length timeline, the team found through computer modeling that the temperature produced waves that synchronized with the length of the day.
The day was about 20 hours; the resonance, the time it takes for a bulge to travel around the planet, was about 10 hours.
The speed-up effect of this atmospheric jiggery-pokery on Earth's rotation rate then neatly countered the slowdown effect of the receding Moon.