After Billion Years, Turns Out Earth Had 19-hours a Day

Jakarta – A new study shows that in the past, Earth had a shorter time duration than it does today, at 19 hours a day.

According to research published in Nature Geoscience on Monday, around 2 billion to 1 billion years ago, a full day lasted five hours faster than today.

The researchers revealed that this was due to the Moon being very close to Earth. Since then, the day on Earth has continued to grow longer as the Moon moved away from the planet and slowed Earth's rotation.

"Over time, the Moon has stolen Earth's rotational energy to push it into a higher and farther orbit from Earth," said the study's lead author, Ross Mitchell, a geophysicist at the Institute of Geology and Geophysics of the Chinese Academy of Sciences.

How did the researchers measure the length of the ancient day? The study says that amid the Proterozoic era, the Moon consistently hovered at a certain distance from Earth, stretching the length of the day by about 19 hours for 1 billion years before it finally started getting longer or longer.

Scientists refer to this period as the "boring billions" due to the relative stability of Earth's tectonic activity, stable climate and slower biological evolution.

For their study, the researchers used a relatively new geological method for measuring historical day length known as cyclostratigraphy.

This technique focuses on variations in rock sediment deposits. Cyclostratigraphy helps researchers identify "Milankovitch cycles", changes in Earth's orbit and rotation that affect the planet's climate.

Analyzing the many cyclostratigraphic records of Milankovitch cycles allowed the researchers to peer into the past and determine why the Moon was tightly bound to the Earth during this period.

In their study, they found the answer to why the Earth has a longer duration of time today than it did a billion years ago is likely related to tides affecting the planet's rotation.

The Moon's gravitational pull controls the tides on Earth, slowing down the planet's rotation.

However, the Sun also exerts a gravitational pull in the form of solar atmospheric tides that occur when the Sun's rays heat the Earth's surface and accelerate the planet's rotation.

Today, the Moon's tides are about twice as strong as the Sun's atmospheric tides. This means they have a greater influence on how fast the Earth rotates.

However, research reveals that billions of years ago, the Earth rotated faster, indicating that the Moon's gravitational pull was weaker than it is today. So, back then, the tides of the Sun and Moon were more balanced.

"Therefore, if in the past these two opposing forces had become equal to each other, such a tidal resonance would have caused the length of the day on Earth to stop changing and remain constant for some time," says study co-author Uwe Kirscher, a research associate at Curtin University in Australia.

Moreover, this long period of 19-hour day duration coincides with a similar slowdown in the increase of oxygen in the atmosphere during the mid-Proterozoic era.

As such, it may have also contributed to the slowdown in the evolution of life on Earth at that time.