About 4.5 billion years agothe earth revolved much faster today. At that time, a day just lasted 10 hours. This was due to the formation of the moon, probably born from a violent collision between the primordial land and a planet of the size of Mars called Theia. At that time, the moon was much closer to our planet, to alone 22,500 kilometers awaythat is to say 17 times closer compared to today.
With the passing of the millennia, the moon has gradually moved away from the earth, slowing down its rotation. This phenomenon should have led to days much longer than 24 hours. In theory, today a terrestrial day should last about 60 hours or more. However, an unexpected balance phase between the gravitational forces of the sun and the moon temporarily blocked this slowdown for a period of one billion years.
The mystery of the “boring billion”
According to a study published on Science Advancesa team of astrophysicians of theUniversity of Toronto found that between Two billion and 600 million years agothe length of the Earth day was blocked a 19.5 hours. The reason? An unexpected compensation between the lunar tides and the atmospheric tides generated by the sun.
Normally, the gravitational attraction of the moon exerts a braking force on earth: the ocean tides created by our satellite generate friction with the seabed, acting as a natural brake on the rotation of the planet. The sun, on the other hand, creates another type of tide, the atmospheric one, which tends to accelerate the terrestrial rotation instead of slowing it down.
For most of the history of our planet, the strength of the moon prevaileddetermining a progressive lengthening of the duration of the day. However, about Two billion years agothings took a different turn: the Natural global warming and a phenomenon known as atmospheric resonance They messed that the solar tide and the lunar one balanced themselves perfectly. The result was a temporary blocking of the slowdown of the terrestrial rotationwhich has maintained the duration of the day for a billion years.
The return to normal
This phase of balance has finished approximately 600 million years agowhen the two sea forces have returned to being unmade. The moon has resumed its braking effect on earth, leading us to the duration of the current day of 24 hours. However, today the thermal tides generated by the sun employ 22.8 hours To complete a cycle around the planet, a value indicating that the terrestrial slowdown is still in progress.
In the future, could we witness a balance between the gravitational forces of the sun and the moon again? According to Norman Murray, astrophysicist of the University of Toronto, the answer is no, at least not in the short term.
The main reason is global warming: The increase in terrestrial temperatures is altering the atmosphere resonance frequency, making a new synchronization between solar and lunar tides more difficult. Consequently, the length of the day will continue to increase more quickly than expectedas explained by Murray:
By increasing the terrestrial temperature with global warming, we are moving the atmospheric resonance frequency, reducing the effect of the sun on the rotation of the earth. As a result, the earthly day will stretch more quickly than it would have happened naturally.
