Earth's Days Are Slowly Lengthening. Here's Why.

Earth's Day Mystery

Researchers for a long time have been keeping a tab on how Earth's days are slowly but surely lengthening. This phenomenon as per experts, is happening because the moon is moving away from the planet, Science Alert reported. This parting has been occurring for millions of years, and so has the phenomenon of adding more time in a day. But for a certain period, due to several forces in play, the lengthening of days stopped, even though the moon continued to move away. During that time, the earth was stuck at having 19.5-hour long days, without any sort of lengthening whatsoever. In 2023, a team of scientists finally found the reason behind this abrupt stop in proceedings and published their findings in Science Advances.

Moon's Impact

The Moon was formed 4.5 billion years ago when Earth's day lasted just a handful of hours, Science Alert reported. As per geological records, the duration of the day increased over time. According to experts, Earth's day has steadily become longer because the moon has been gradually receding at a rate of around 3.78 centimeters (1.49 inches) per year. The phenomenon in play here is the moon's gravitational influence, which impacts the tides of Earth's oceans. The moon orbits around the Earth and creates ocean bulges on either side of the planet. The moon's gravity pulls on those bulges and leads to what is known as a braking effect, which slows down the Earth's rotation. The whole process adds around 1.7 milliseconds to Earth's day every century. This phenomenon is similar to what happens with figure skaters, they slow down after extending their arms.

Sun's Impact

Sun does not produce any effect on the ocean, but does have an impact on the atmosphere, Science Alert reported. "Sunlight also produces an atmospheric tide with the same type of bulges," Norman Murray, an astrophysicist from the University of Toronto in Canada explained. "The Sun's gravity pulls on these atmospheric bulges, producing a torque on the Earth. But instead of slowing down Earth's rotation like the Moon, it speeds it up." Moon's impact far outweighs the sun's impact, so Earth's days have lengthened rather than shortened.

Earth's Steady Period

From around two billion years ago up until 600 million years ago, the sun's impact overtook the moon's impact and days remained relatively stable. This was because the sun's effect received support from another property called resonance. The atmosphere during that period had become warmer which allowed the sun's gravitational pull to facilitate larger bulges, the University of Toronto reported. At the same time, the atmosphere's natural resonance (frequency with which waves travel through the medium) was also enhanced. The atmospheric resonance and Earth's rotation synchronized with each other, helping the sun’s tidal pull become strong enough to counter the lunar tide. "It's like pushing a child on a swing," Murray said. "If your push and the period of the swing are out of sync, it's not going to go very high. But, if they're in sync and you're pushing just as the swing stops at one end of its travel, the push will add to the momentum of the swing, and it will go further and higher. That's what happened with the atmospheric resonance and tide." Hence, for that period the Earth's day was stuck at around 19.5 hours. 

Interconnection With Climate Crisis

Researchers associated with the study believe that the analysis of what happened during the Earth's steady period is important, as it helps humans to fully grasp the consequence of climate change, the University of Toronto reported. Similar to two billion years ago, the earth's atmosphere is heating up again, and as the study showcases, tidal imbalance is a huge after-effect of this change, that shouldn't be discounted. "As we increase Earth's temperature with global warming, we’re also making the resonant frequency move higher — we’re moving our atmosphere farther away from resonance. As a result, there's less torque from the sun, and therefore, the length of the day is going to get longer, sooner than it would otherwise," Murray explained.