When we think of time, we usually imagine it as an unchanging stream that moves uniformly. In reality, however, time on Earth is changing. Scientists have long known that the Earth rotates on its axis, a process that is not constant. Days get longer or shorter depending on various factors. Recent studies have shown that the length of the day may have been determined by the amount of oxygen in the Earth’s atmosphere, which in turn was determined by the abundance of photosynthetic organisms.
Interactions between the Earth and the Moon are slowly pushing our satellite away, in the process slowing down the Earth’s rotation. However, this seems to be a much less uniform process than has been assumed, since the lengthening has stopped at least once. Over a long period starting about two billion years ago, it may have stopped completely, which may have been caused by changes in the Earth’s atmosphere.
If you are among those people who have a natural tendency to go to bed a little later each night, as if you were used to a 25-hour day, you might consider yourself a Martian. Alternatively, you might just consider yourself ahead of your time, because one day the Earth’s rotation will slow down enough to make the day an hour longer.
A new article argues that we were wrong in predicting the speed of the process of slowing down the Earth’s rotation. “Over time, the Moon has stolen the energy of Earth’s rotation to put it in a higher orbit further from Earth,” said study author Professor Ross Mitchell of the Chinese Academy of Sciences. Slower rotation inevitably lengthens the day.
“Most models of Earth’s rotation predict that the length of the day has consistently gotten shorter and shorter in the past,” added study author Dr. Uwe Kirscher of Curtin University. Instead, however, Mitchell and Kirscher concluded that Earth’s days first got longer after the moon formed, but then stopped for about 19 hours before the lengthening resumed.
The period of little or no change lasted from two to one billion years ago. This coincides with an era that geologists call the “boring billion” because so little happened in the period before the sudden explosion of multicellular life. The pair don’t think it’s a coincidence.
The delay occurred because the moon is not the only celestial object affecting our days. Solar heat causes tides in the atmosphere that accelerate rotation. Currently, solar tides are much weaker than lunar tides and only slightly mitigate the influence of the Moon. However, when the Moon was closer, “The frictional relationship between the Earth and the Moon was weaker because of the Earth’s faster rotation,” Mitchell said.
Mitchell and Kirscher wondered if the Moon’s force could have been so small for some time that the Sun completely neutralized it, and their paper confirms it. Even with the relative weakness of the Moon, it would have required a stronger solar influence, which the authors attribute to the composition of the atmosphere at the time, when oxygen levels were low and ozone high.
Mitchell and Kircher’s study is important for understanding Earth’s past and its future. They showed that the process of slowing down the Earth’s rotation is not constant and can vary depending on various factors, such as the Moon and the composition of the atmosphere. This may have important implications for future generations who may face longer or shorter days.