Earth’s Rotation Is Slowing Down, And Could Explain Why We Have Oxygen

Ever since it formed approximately 4.5 billion years ago, Earth’s rotation has been gradually slowing, resulting in progressively longer days over time.

Although this deceleration isn’t noticeable on human timescales, it has caused significant changes over eons. One of the most profound impacts, at least for life on Earth, is the connection between lengthening days and the oxygenation of Earth’s atmosphere, as highlighted by a 2021 study.

The study suggests that blue-green algae, or cyanobacteria, which began thriving around 2.4 billion years ago, were able to produce more oxygen as a by-product of their metabolism because Earth’s days had grown longer.
“An enduring question in Earth sciences has been how did Earth’s atmosphere get its oxygen, and what factors controlled when this oxygenation took place,” microbiologist Gregory Dick of the University of Michigan explained in 2021.
“Our research suggests that the rate at which Earth is spinning – in other words, its day length – may have had an important effect on the pattern and timing of Earth’s oxygenation.”


This story has two major components that initially seem unrelated. The first is Earth’s slowing spin, caused by the Moon’s gravitational pull, which creates a deceleration as the Moon gradually moves farther away.

Fossil records indicate that 1.4 billion years ago, a day lasted just 18 hours, and 70 million years ago, days were about half an hour shorter than today. Evidence shows that Earth gains approximately 1.8 milliseconds per century.

The second component is the Great Oxidation Event, when cyanobacteria became so abundant that Earth’s atmosphere experienced a sharp rise in oxygen levels. This oxygenation was crucial for the emergence of life as we know it.

Without this event, scientists believe that life as we know it wouldn’t have emerged. Despite their unassuming reputation today, cyanobacteria played a pivotal role in Earth’s history. Yet many questions remain, including why oxygenation happened when it did rather than earlier.

Earth’s Rotation Is Slowing Down, And Could Explain Why We Have Oxygen
Microbiologist Gregory Dick from the University of Michigan. (University of Michigan)

Scientists working with cyanobacterial microbes made an intriguing connection. In the Middle Island Sinkhole in Lake Huron, microbial mats resembling those from the Great Oxidation Event can still be found.

These mats consist of oxygen-producing purple cyanobacteria and sulfur-metabolizing white microbes. At night, the sulfur microbes dominate, but when the Sun rises, they retreat, allowing the cyanobacteria to photosynthesize and produce oxygen.

“Now they can start to photosynthesize and produce oxygen,” said geomicrobiologist Judith Klatt of the Max Planck Institute for Marine Microbiology in Germany.
“However, it takes a few hours before they really get going, there is a long lag in the morning. The cyanobacteria are rather late risers than morning persons, it seems.”

This limited window of oxygen production sparked oceanographer Brian Arbic’s curiosity about whether changes in Earth’s day length influenced photosynthesis over its history.
“It’s possible that a similar type of competition between microbes contributed to the delay in oxygen production on the early Earth,” Klatt noted.

To test this hypothesis, the team conducted experiments with microbes both in their natural environment and in the lab. They also created detailed models linking sunlight to microbial oxygen production and tying this to Earth’s history.

“Intuition suggests that two 12-hour days should be similar to one 24-hour day. The sunlight rises and falls twice as fast, and the oxygen production follows in lockstep,” explained marine scientist Arjun Chennu of the Leibniz Centre for Tropical Marine Research in Germany.
“But the release of oxygen from bacterial mats does not, because it is limited by the speed of molecular diffusion. This subtle uncoupling of oxygen release from sunlight is at the heart of the mechanism.”

These findings were incorporated into global models of oxygen levels, showing that longer days were linked to increased oxygen. This was true not only for the Great Oxidation Event but also for the Neoproterozoic Oxygenation Event, which occurred between 550 and 800 million years ago.

“We tie together laws of physics operating at vastly different scales, from molecular diffusion to planetary mechanics. We show that there is a fundamental link between day length and how much oxygen can be released by ground-dwelling microbes,” Chennu said.
“It’s pretty exciting. This way we link the dance of the molecules in the microbial mat to the dance of our planet and its Moon.”

The research was published in Nature Geoscience.



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