The Earth has been slowing down ever since it was created which was 4.5 billion years ago. Our days used to be a lot shorter, but it’s the Moon that has been pulling, ever so slightly, which has made the days longer. For us, the change every one hundred years is so tiny at 1.8 milliseconds only, that it goes unnoticed. However, it has been billions of years, and this really small change has created a huge impact.
According to researchers at the University of Michigan and the Max Planck Institute, the days may have been longer and this giving the first ever cyanobacteria, long enough to spend the entire time during the daylight hours to release oxygen into the atmosphere. This is known as oxygenation which caused the Great Oxidation Event that occurred 2.4 million years ago, and also the Neoproterozoic Oxygenation Event that occurred a few hundred million years later.
If those shifts didn’t occur, it would really be difficult to support life (including us).
Why is the Earth’s spin slowing down?
In a way, it is the Moon’s fault. Its gravity forms tides, which acts like a brake on the Earth’s spin. At the same time, the Moon is slowly drifting away. It, however, has a parting gift for us; slowly drifting away means gifting us longer hours in a day.
About 1.4 billion years ago, a day took only 18 hours. Days were still half an hour shorter than they are now 70 million years ago. The longer the day, the more time microbes had to work their magic.
At the same time, the Great Oxidation Event was happening. Cyanobacteria were photosynthesizing in ancient oceans and oxygenating the planet for the very first time. Life on Earth became possible because the atmosphere was now filled with oxygen.
Cyanobacteria: The lazy geniuses of early life
Scientists got clues from a sinkhole in Lake Huron. Microbial mats on the bottom of the sinkhole are associated with primitive colonies of cyanobacteria. Within the mats, two forms of microbes compete: the purple cyanobacteria that produce oxygen and the white microbes that live on sulfur.
Every evening, sulfur-eaters occupy the uppermost layer. When the sun rises, sulfur-eaters go down and the cyanobacteria come up to look for sunlight. But, unlike the sulfur-eaters, they are not as active. Judith Klatt of the Max Planck Institute describes them as “late risers.” It takes them hours after the sun rises to start oxygen production.
That lag time means short days left little room for oxygen production. But as days grew longer, the cyanobacteria had a bigger window to photosynthesize—and the oxygen levels began to climb. Oceanographer Brian Arbic from the University of Michigan connected the dots: maybe Earth’s slowing spin was the hidden key to the timing of oxygen spikes.
From microbes to a breathing planet
To test the idea, researchers studied these microbes, then modeled how day length influenced oxygen output. Marine scientist Arjun Chennu explained it beautifully: even though a 12-hour day might seem like it should equal half of a 24-hour day, it doesn’t work that way. Oxygen release lags behind sunlight because of diffusion limits, so longer days actually lead to more oxygen production overall.
When the team fed this data into global models, they found that the timing matched not only the Great Oxidation Event but also the later Neoproterozoic Oxygenation Event, about 550 to 800 million years ago.
As Chennu put it, the research connects “the dance of molecules in microbial mats to the dance of our planet and its Moon.”
Without the Moon’s steady tug slowing down the Earth’s rotation, cyanobacteria might never have had enough daylight to fill the atmosphere with oxygen. And without oxygen, none of us would be here.