The gravitational interactions that helped us avoid 60 hours a day – Ars Technica

Most of us wish we had more than 24 hours in a day to get everything done and actually breathe. What if each day gave us more than twice as much time? If it weren’t for a phenomenon that stopped the lengthening of Earth’s days billions of years ago, it probably would have happened.

Earth did not always have 24 hours. There were less than 10 hours in a day when the Moon first appeared about 4.5 billion years ago, but it has grown longer as lunar tidal forces gradually slow the Earth’s rotation. But there was a long period when the days did not grow old at all. Now astrophysicists have found that from 2 billion to 600 million years ago, days were about 19.5 hours long because several tidal forces canceled each other out and kept the Earth spinning at the same speed for more than a billion years. If it never happened, our current days might be more than 65 hours long.

The research team said in a study recently published in Science advances.

Give it a spin

So how do tidal forces from the sun and moon affect the Earth’s rotation? Lunar tidal forces are generated by the moon’s gravity. This is why the side of our planet closest to the moon and the side farther away will bulge and the oceans will experience higher tides (bulges affect land but are not noticeable to the naked eye). The Moon’s gravity pulls on these bulges, thus resisting Earth’s rotation. The locations of these bulges change as the Earth rotates, creating friction that also slows that rotation.

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There are two solar tides that produce torque, a twisting force that affects rotation. The first type of solar moment is the solar tidal moment, and it works in the same way as the moon, causing very small changes in tides in the oceans, and thus slowing down the Earth’s rotation.

The second type is thermal tidal moment. When sunlight heats the atmosphere, it causes it to expand, creating another knob that the sun’s gravity can interact with. This effect causes the Earth to spin faster. Although the Sun’s gravity is stronger, so is our star 390 again From the Earth more than from the Moon, so the lunar tides are generated Double strength. As a result, the days continue to grow a little longer.


Two billion years ago, all of this changed. Earth’s atmosphere was much warmer. This affected the heat waves that sunlight created in the atmosphere, with higher temperatures meaning higher wave speeds. The frequency at which those waves travel through the atmosphere created an atmospheric resonance, adding to their effect. For a billion years, this resonance and the length of the day will remain in sync, with atmospheric waves resonating each time Earth completes about half a turn.

Since the Earth’s rotation period was almost twice that of the resonance period, the tides in the atmosphere caused by the Sun became stronger, since the Sun’s gravity had more mass to work with. The result is a torque roughly equivalent to that of the tides on the surface of the Moon. The earth ended up not moving slower or faster. The days won’t grow back until 600 million years ago – a billion years after the start of the chime.

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The team conducting the study confirmed the result of their computational models by examining geological evidence of high and low tides from extremely ancient rock formations. The astrophysicists also said in the study, “The long duration and relatively recent occurrence of this resonant state may be responsible for the fact that the day is currently 24 hours long.”

Could rising temperatures due to global warming cause desynchronization of circulation and lengthening of days? it’s happening now. The greater the desynchronization of resonance and rotation, the less solar tidal forces were able to counteract the lunar tidal forces that slowly extended days on Earth over eons. We could all probably use a few extra hours in the day, but not at the expense of our planet.

Science Advances, 2023. DOI: 10.1126/sciadv.add2499 (About DOIs).

Elizabeth Raine Creature Writes. Her work has appeared on SYFY WIRE,, Live Science, Grunge, Den of Geek, and Forbidden Futures. When she’s not writing, she’s either shape-shifting, drawing, or masquerading as a character no one has ever heard of. Follow her on Twitter: @hravenrayne.

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