Earth’s Ancient Day Length Stalled at 19 Hours for a Billion Years, Study Finds

New Study Reveals Earth’s Ancient Day Length Stalled at 19 Hours for a Billion Years

Contrary to previous beliefs, Earth’s day length was not consistently shorter in the past, but instead may have remained stable at around 19 hours for approximately one billion years, according to a recent study published in Nature Geoscience. This intriguing period of stable day length coincides with two significant rises in atmospheric oxygen, suggesting that Earth’s rotation may have played a role in shaping its atmospheric composition.

The concept of a 24-hour day is something we take for granted in the modern world. However, in Earth’s distant past, days were even shorter due to the Moon being closer to our planet. Over time, the Moon has gradually stolen Earth’s rotational energy, causing it to move into a higher orbit and further away from Earth. This phenomenon has resulted in the lengthening of Earth’s day.

Most models of Earth’s rotation predict a consistent decrease in day length as we go further back in time. However, the recent study conducted by geophysicist Ross Mitchell and researcher Uwe Kirscher challenges this notion. They discovered that the change in day length over time was not a gradual process.

To measure ancient day length, researchers have traditionally relied on records from sedimentary rocks that preserve fine-scale layering in tidal mud flats. By counting the number of sedimentary layers per month caused by tidal fluctuations, scientists can estimate the number of hours in an ancient day. However, these tidal records are rare and often disputed.

In this study, Mitchell and Kirscher utilized a different method called cyclostratigraphy. This geological technique uses rhythmic sedimentary layering to detect Milankovitch cycles, which reflect how changes in Earth’s orbit and rotation impact climate. Two specific Milankovitch cycles, known as precession and obliquity, are related to the wobble and tilt of Earth’s rotation axis in space. The faster rotation of early Earth can be detected through shorter precession and obliquity cycles in the past.

The researchers took advantage of a recent increase in Milankovitch records, with over half of the data for ancient times generated in the past seven years. This allowed them to test an alternative idea about Earth’s paleorotation, which suggests that day length might have stalled at a constant value in the distant past.

The study proposes that in addition to the lunar oceanic tides caused by the Moon’s pull, Earth also experiences solar atmospheric tides related to the heating of the atmosphere during the daytime. While solar atmospheric tides are not as strong as lunar oceanic tides, they would have had a more significant impact when Earth was rotating faster in the past. Unlike the Moon’s pull, which slows down Earth’s rotation, the Sun’s tide pushes Earth, potentially speeding up its rotation.

If these two opposing forces were to become equal in the past, a tidal resonance could have occurred, causing Earth’s day length to stop changing and remain constant for a certain period. The data compilation from the study supports this theory, showing that Earth’s day length stalled at around 19 hours between two to one billion years ago, a period often referred to as the “boring billion.”

Interestingly, this period of stable day length coincides with two significant rises in atmospheric oxygen. Timothy Lyons, a researcher from the University of California, Riverside, who was not involved in the study, finds it fascinating to think that the evolution of Earth’s rotation could have influenced the composition of the atmosphere. The study suggests that the rise of oxygen levels on Earth had to wait for longer days, allowing photosynthetic bacteria to generate more oxygen each day.

This new research sheds light on the complex relationship between Earth’s rotation, atmospheric composition, and the evolution of life on our planet. It highlights the importance of studying Earth’s ancient history to better understand the processes that have shaped our world over billions of years.

Reference:
“Mid-Proterozoic day length stalled by tidal resonance” by Ross N. Mitchell and Uwe Kirscher, Nature Geoscience, 12 June 2023, DOI: 10.1038/s41561-023-01202-6

What mechanisms may have contributed to the unusually stable rotation of Earth for approximately one billion years, and how did this stability potentially influence atmospheric oxygen levels

Of around 19 hours for a significant period of time.

The team examined over 1,000 ancient sedimentary records from various locations around the world. They specifically looked for evidence of short precession and obliquity cycles, which would indicate a faster rotation of Earth in the past. The analysis showed that these short cycles were indeed present during a specific period, approximately one billion years ago.

This finding challenges the previous belief that Earth’s day length gradually decreased over time. Instead, it suggests that there was a stable period where the rotation rate remained relatively constant at around 19 hours. This stability coincided with two significant rises in atmospheric oxygen, known as the Great Oxygenation Events, which occurred about 2.4 billion years ago and 800 million years ago.

The researchers propose that Earth’s rotation may have played a role in shaping its atmospheric composition during these periods. The faster rotation could have influenced the distribution of sunlight and heat on the planet, which in turn affected weather patterns and allowed for the accumulation of oxygen.

Notably, the stable day length of around 19 hours lasted for approximately one billion years. This is a significant timescale in Earth’s history and suggests that the planet’s rotation was unusually stable during this period.

Further research is needed to understand the mechanisms behind this stability and its relationship with atmospheric oxygen levels. The findings from this study highlight the complexity of Earth’s past and the potential influence of its rotation on key geological and atmospheric events.