Chapter 1: The Boring Billion

In recent discussions, scientists and geologists have become particularly fascinated by a curious era in Earth's timeline known as the "boring billion." This phase, which lasted from approximately 2 billion to 1 billion years ago, was characterized by a significant lack of major evolutionary developments on our planet, leading to a stable existence for about a billion years.

During this time, life was predominantly simple, single-celled organisms, and the climate showed little variation. Additionally, tectonic activity and volcanic eruptions were minimal, making this period particularly appealing for scientific exploration. This was the motivation behind a recent study by geophysicists Ross Mitchell and Uwe Kirscher, who aimed to delve deeper into this phenomenon.

Their research uncovered that this "boring billion" coincided with a unique state of Earth's rotation, where days were merely 19 hours long. They termed this phenomenon "stalling," describing a period in which the Earth maintained a consistent rotational speed. This rapid rotation resulted in significantly shorter days compared to our current 24-hour cycle, as illustrated in the graph below.

Graph by Mitchell and Kirscher in Nature Geoscience

This revelation challenges earlier beliefs that Earth's rotation has been gradually decelerating over billions of years. According to Mitchell and Kirscher, the stability of Earth's rotation was maintained by a delicate balance of opposing forces. As the Moon slowly receded from Earth, it began to extract rotational energy, leading to a gradual slowdown.

However, during the "boring billion," the Moon was positioned closer to Earth and maintained a stable orbit, exerting a weaker gravitational influence. This reduced energy transfer allowed for other forces to stabilize the rotation.

Mitchell and Kirscher also posited that rising oxygen levels on Earth may have contributed to this stabilization. The increase in oxygen prior to the "boring billion," known as the Great Oxidation Event, led to the formation of an ozone layer that absorbed more sunlight than water vapor. This contributed to climate stability, which, in turn, is believed to have supported a consistent rotation of the Earth.

In their study, they concluded, "We found that the day length stalled at about 19 hours for around 1 billion years during the mid-Proterozoic. We propose that the acceleration torque of atmospheric thermal tides from solar energy balanced the deceleration torque of lunar oceanic tides, temporarily stabilizing Earth's rotation. This stalling aligns with a period of limited biological evolution known as the boring billion."

As the "boring billion" drew to a close, the researchers believe an oxygen exit (referred to as Oxit) occurred, leading to a gradual slowdown in rotation, ultimately reverting to the pre-stabilization conditions. This phenomenon explains why we observe an incremental increase in the length of a year, approximately 0.000015 seconds longer each year, as the Moon continues to slow down Earth's rotation.

Mitchell and Kirscher stress the importance of ongoing research to further clarify the mechanisms driving this phenomenon, advocating for a deeper understanding of the intricate relationship between the Moon, atmospheric tides, and the rotation of our planet.

This video, titled "Day On Earth Was 19 Hours Long For a Billion Years and The Reason is Very Surprising," explores the surprising findings about Earth's ancient rotation.

In another insightful video, "Has a Day on Earth Always Been 24 Hours? | Earth's Rotation," the discussion continues on how Earth's rotation has evolved over time.