Scientists Report Earth Has Remained Stagnant at a 19-Hour Day for a Billion Years

While Earth may currently be spinning faster, resulting in a 24-hour day, the presence of the moon and its gradual drift away from Earth is the main factor influencing the duration of a day on our planet.

There are other contributing factors such as processes in Earth’s core and solar tides caused by atmospheric heating, but the tidal forces from the moon have the greatest impact on the length of a day on Earth.

Interestingly, the length of a day on Earth has not always increased over time. There appears to have been a period of stalling, which could have led to a flourishing of plant life and a surge in oxygen levels.

Remarkable Findings

“Over time, the moon has stolen Earth’s rotational energy to boost it into a higher orbit farther from Earth,” explained Ross Mitchell, a geophysicist at the Institute of Geology and Geophysics of the Chinese Academy of Sciences and the lead author of a new study published today in Nature Geoscience.

It appears that Earth’s changing orbit and the angle at which it spins could have had significant implications for ancient Earth.

Not a gradual change

The study challenges the prevailing notion of a slow and steady change in day length throughout Earth’s history, which is predicted by most models of Earth’s rotation.

Prior research has primarily focused on studying tidal mud flats preserved in sedimentary rocks to determine day length in ancient times. However, this new research utilizes the science of cyclostratigraphy, which incorporates long-term astronomical cycles found in sediment layers. These cycles, known as Milankovitch cycles, include Earth’s orbital shape (eccentricity) and the angle and direction of its axis of rotation (obliquity and precession).

Milankovitch cycles

The variations in Earth’s obliquity and precession are a result of its wobbling motion as it spins. This can be observed with a spinning top, as the angle of the axis changes over time. According to Kirscher, “The faster rotation of early Earth can therefore be detected in shorter precession and obliquity cycles in the past.”

Precession occurs over a period of 22,000 years, causing Earth’s axis to point towards different stars. For instance, Polaris is currently the North Star, but 12,000 years ago, Vega held that position, and it will do so again in another 12,000 years.

These astronomical phenomena are crucial for calculating Earth’s paleorotation, but the lack of available data sources has made it a controversial topic. However, the researchers note that advancements in data collection over the past seven years have provided new insights. “We realized that it was finally time to test a kind of fringe, but completely reasonable, alternative idea about Earth’s paleorotation,” said Mitchell.

19-hour day

The new data suggests that day length may have remained constant at around 19 hours in Earth’s distant past. This phenomenon was not due to the moon slowing down Earth’s rotation, but rather, the sun speeding it up.

Approximately one to two billion years ago, Earth rotated at a faster rate, weakening the tidal pull of the moon. At the same time, solar atmospheric tides would have been stronger and eventually balanced out the lunar forces. Kirscher explained, “Such a tidal resonance would have caused Earth’s day length to stop changing and remain constant for some time.”

Oxygen surge

This period of a 19-hour day coincides with two significant surges in Earth’s oxygen levels. This correlation suggests that the extended day length may have allowed plants ample time for photosynthesis, contributing to an increase in atmospheric oxygen. Timothy Lyons from the University of California, Riverside, who was not involved in the study, commented, “It’s fascinating to think that the evolution of Earth’s rotation could have affected the evolving composition of the atmosphere.”

Wishing you clear skies and wide eyes.

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