As you’re likely well aware, one complete rotation of the Earth around its axis takes 24 hours. However, this was only sometimes the case, and our planet has a long history of changing day lengths. As a result, it can be challenging to understand how we got where we are today, but a new study provides clues to the past.
According to a new study published in Nature Geoscience, our current 24-hour cycle came about due to a delicate balance of gravitational forces. Throughout its history, the rotation of our planet has been slowed down by the pull of the Moon and other planetary bodies. Fortunately, this slowdown has been relatively minor and hasn’t had much of an impact on life as we know it.
But scientists have known that the rotation of our planet has sometimes been rocky and uneventful. In fact, Earth experienced a significant deceleration in some geological periods that caused days to lengthen significantly. This was likely due to a significant decrease in the rate of tectonic activity, which would have reduced the friction between the planet’s surface and its inner core. During this period, multicellular life began to appear on our planet.
The latest research by two geophysicists suggests that during the period known as the “boring billion,” or about 620 million years ago, the Earth’s rotation was nearly halted entirely. The researchers used geological data, including tidal rhythmites and patterns of mud deposits spread out by the ocean’s tidal force and preserved in rock, to figure out that a day on Earth was only 19 hours.
During this period, which the researchers call a “tidal resonance,” the opposing forces of atmospheric thermal tides and lunar ocean tides struck such a delicate balance that they became equal. This tidal resonance, they believe, allowed the length of a day to remain at 19 hours for a very long time. Interestingly, this stalling occurred roughly two and a billion years ago—the so-called boring billion—and coincided with the two most significant increases in oxygen levels on Earth.
Scientists have long known that gravity pulls on our planet and slows its rotation when the Moon moves closer to Earth. But they were unaware that this process could get to a point where the forces of the Moon and Sun become equal, creating a tidal resonance that stops the length of the day from ever increasing or decreasing.
The research by Mitchell and Kirscher shows that this did occur. But they need to figure out why it stopped and are presently working on compiling new data to figure out the answer. They’re hopeful that further work will reveal whether an injection of ozone and sunlight can help re-sync up the forces and rekindle the 19-hour day. This might allow scientists to learn more about the relationship between tidal resonance, the rise of oxygen, and the evolution of multicellular life on our planet.
