Earth’s Rotation: Why is the 24-hour day?

Mountains of seas caused by the moon act like brake shoes and slow down the Earth’s rotation. If the rotation of our planet depended only on the Earth’s satellite, then the day should be 60 hours. But the Sun stopped slowing Earth’s rotation for about a billion and a half years, giving us the length of the 24-hour day. This is the conclusion reached by a research team from Canada and France through geological investigations of tidal sediments and with the help of climate models. Scientists concluded that global warming In the journal “Science Advances”but the slowdown could intensify in the future.

The previous days are much shorter

The young Earth 4.5 billion years ago rotated much faster than it does today. The day was well under ten hours. At the time, the newly formed Moon was still orbiting the Earth in a much narrower orbit and the tides were much stronger than they are today. Because the Flood Mountains act as a brake, Earth’s rotation has slowed steadily – until about two billion years ago. As investigations Norman Murray From the University of Toronto in Canada and his team’s presentation, this process stopped at that time – the length of the day had remained constant at about 19.5 hours for 1.4 billion years. Only then did it continue to increase until today.

Atmospheric tides

With the help of climate models, such as those used to predict current global warming, researchers have now been able to track down the cause of the deadlock. “Radiation from the sun also causes tides in Earth’s atmosphere,” Murray explains. Unlike lunar tides, these atmospheric tides accelerate the Earth’s rotation, but are much smaller in comparison to these tides and therefore are usually of little importance. However, not always.

Because the Earth’s atmosphere can vibrate like a bell. The fluctuation depends on the atmospheric temperature. Two billion years ago the atmosphere was much warmer than it is today – and an “echo” occurred: the shaking of the atmosphere suddenly coincided with the period of rotation – and thus also with the tides caused by solar radiation. Because of the resonance, the solar tides increased and their effect on the Earth’s rotation became so strong that it compensated for the slowing down of the Moon.

Murray compares this phenomenon to a baby’s swing: “If you give the baby a push independent of the movement of the swing, the swing won’t go up very much. However, if you push in the same rhythm as the swing, i.e. with resonance, the swing moves higher and higher. Likewise, the atmospheric resonance increased Tides in the sun.”

Warming lengthens the days

Not only does the study by Murray and Co. show why the day on Earth is 24 hours a day. It also provides a glimpse into the future of Earth. The oscillation of Earth’s atmosphere lasts for 22.8 hours today – so it’s not proportional to the length of the day, but it’s not too far off either.

“As global warming continues to increase the temperature of the atmosphere, this difference will increase,” says Murray. “As a result, the Sun’s influence on Earth’s rotation continues to decrease — and day length increases faster than warming does not occur.” However, evolution is nothing to worry about: the length of the day is currently decreasing by 1.7 milliseconds per century – even if it were much longer, the decrease would be meaningless in human terms.