December 5, 2023

If you’ve ever felt like you needed more hours in your day, how does 60 sound? A new study suggests that if the standoff between the sun and the moon hadn’t interfered with Earth’s rotation for more than a billion years, we’d be on a 60-hour day today.

A day seems like a fairly constant amount of time, but in fact today is longer than the same day a century ago — albeit by only 1.8 milliseconds. This is because the moon is gradually moving away from the earth, which causes the earth’s rotation rate to gradually slow down. Of course, if the earth’s rotation rate is slower, the days will become longer.

During Earth’s lifetime, days have many different lengths. About 4.5 billion years ago, shortly after the Moon first formed, the length of day was less than 10 hours. Around 70 million years ago, towards the end of the reign of the dinosaurs, that lengthened to the more familiar 23.5 hours.

But that rate of change isn’t entirely plausible, according to researchers at the University of Toronto. If daylight continues to lengthen at a steady rate, today’s length will be about 60 hours. It’s interesting to think about cultural and even biological differences between humans and other animals.

So what happened? The researchers investigated the hypothesis that a specific combination of factors from the Earth, Moon and Sun, combined in the right way, could prevent the slowing of the rotation over long periods of time. By examining geological evidence and atmospheric research tools, it seems to make sense.

We all know that the moon is responsible for ocean tides, as its gravity pulls the water into “bulges” in different directions throughout the day. This is also why the moon slows down the rotation of the earth, thanks to gravity and the friction caused between the tides and the ocean floor. But that’s not the only force acting on Earth’s rotation.

“Sunlight also produces atmospheric tides with the same type of bulge,” said Professor Norman Murray, corresponding author of the study. “The sun’s gravity pulls on these atmospheric bulges, creating a torque on Earth. But it doesn’t do it like the moon does. Instead of slowing down the Earth’s rotation, it speeds up the Earth’s rotation.”

However, the moon’s influence is about 10 times that of the sun, so it wins the tug of war, and the Earth’s rotation slows down. But the researchers involved in the study found that these two factors were in balance some 2.2 billion years ago.

At that time, the air in the atmosphere was warmer, so the bulge created by the sun moved faster through the atmosphere, taking about 10 hours to circle the Earth. Fortunately, by then the Earth’s rotation had slowed down to 20 hours per day. Since the two tides are in a 1:2 resonance, the atmospheric tides are strengthened and the influence of the sun is stronger.

The end result is that the sun and moon balance each other out, so the length of the day stops growing. And just like that, it was locked in for 19.5 hours, for a staggering 1.6 billion years. Without a long pause, we’d be seeing 60 hour days and very different lifestyles right now.

According to the team, this research shows that climate change may have interesting effects on the length of daylight in the future.

“As global warming causes the Earth to heat up, we also make the resonance frequency higher — we move the atmosphere away from the resonance,” Murray said. “Therefore, there is less torque from the sun, so the length of the day lengthens faster than it would otherwise.”

The study was published in the journal scientific progress.

source: University of Toronto