If you feel like you never have enough hours in the day to do everything you want to do, don’t worry. You just have to wait 200 million years for the Earth to have an extra hour. Yes, the planet’s rotational forces are conspiring to help us find time to do all our household chores and work projects. Although we know that we probably won’t be around in 200 million years, we can always fantasize about a day when we have 60 extra minutes to do whatever we want.
Joking aside, astronomers have compiled almost 3,000 years of celestial records and have seen that, indeed, with each rotation of the planet, the day on Earth is 2,000 seconds longer than it was 2,000 years ago, as the planet’s rotation gradually slows down. Our planet is nothing more than a giant spinning top whirling around the solar system, losing rotational force almost imperceptibly over time.
A fraction of a second every century or so
Since World War I, our planet has gained a fraction of a second. To make all these calculations, researchers at Durham University and the UK Nautical Almanac Office compiled historical accounts of celestial events such as eclipses from 720 BC to 2015. Older records came from Babylonian clay tablets—in cuneiform script—and ancient Greek texts, such as Ptolemy’s writings from the 2nd century. They also consulted writings from Ancient China and the Persian Empire.
The ancient records mainly recorded times and places where people had witnessed various stages of solar and lunar eclipses. From 1600 AD onwards, more lunar occultations were recorded, in which the moon passed in front of particular stars and blocked them from view. With all this information, the researchers compared historical records with a computer model that calculated where and when people would have seen these events if the Earth’s rotation had remained constant.
That’s when astronomers noticed the discrepancies. The theoretical calculation was one thing, but the actual place and time when the eclipses were observed was another. This means that the Earth’s rotational speed has varied throughout human history.
Earth rotation at stake
Although the Earth formed from a cloud of dust and gas 4.5 billion years ago, scientists believe it received an additional boost when a small object the size of Mars collided with the young planet and ejected the material that gave rise to our beloved moon. Before that cataclysm, the Earth appeared to have a six-hour day cycle.
Astronomers have long known that the Earth’s rotation is gradually slowing down. The main effect of this slowdown comes from the tides caused by the Moon’s gravity. Ultimately, the accumulation of water drags the Earth down as it rotates beneath it. However, tides are not the only force at play.
Since the end of the last ice age, land masses that were previously buried under sheets of frozen water have been released and returned to their place. This caused the Earth to become less flattened. Like a figure skater, the Earth spins faster if its poles are less compressed.
There are also other factors: changes in sea level and changes in the rocky mantle of the Earth’s core with electromagnetic forces are things that affect the Earth’s rotation. The different forces slow down the Earth’s rotation almost imperceptibly to humans, but at irregular levels. These cycles of change in the Earth’s rotation can occur every 1,500 years.
Just as trees can live for hundreds of years, geological processes occur over very long periods of time, in which humans are merely ants. The study of Earth is nothing more than the long-term observation of the planet we inhabit. We can only be guardians of the knowledge passed down to us by our ancestors and leave an accurate record of what we have observed for future generations. One day, the Earth will have 25 hours, but our great-grandchildren will enjoy at most an extra 1/1000th of a second compared to us.