Although you may not notice (and how could you?), Earth spins a tiny bit more slowly as centuries pass. That simple fact can change how much oxygen fills the air you breathe.
The slowdown comes from the tug of the Moon on our oceans. Tides —no matter how we underestimate them— act like brakes. In fact, they are able to spin energy into heat and stretching the length of a day over very long times. Long ago, a “day” was much shorter than 24 hours. Today it’s longer than it used to be by (just milliseconds per century, mind you), but over billions of years that adds up in a big way.
But, how does that relate to oxygen?
It all has to do with microbial mats. And no, we are not referring to that bathroom matt you should have scorched at 130ºF in your washing machine months ago, before it starts crawling on its own.
We are talking about layered “mats” of microbes that grow in shallow water. The top chefs in this livelasagna were purple-green cyanobacteria, which use sunlight to make food and release oxygen. In the morning, they don’t blast off immediately; there’s a lag before photosynthesis ramps up. Meanwhile, other microbes that like sulfur compete for space and resources.
Because oxygen seeps (diffuses) out of mats slowly, the timing of sunlight becomes a big deal. Short days mean the sun sets soon after the cyanobacteria finally get going. Longer days give extra afternoon hours for oxygen to leak into the water and, eventually, the air.
The lake sinkhole experiment that unlocks the story
To test this idea, scientists worked in a weird, beautiful spot in Lake Huron called Middle Island Sinkhole (we promise it’s prettier looking than what it sounds like). Its chemistry and light make it a good stand-in for parts of ancient coastlines. Teams measured real mats in the lake and then ran careful lab experiments that stretched or squeezed the length of “day.”
The pattern was clear: as “day” got longer, mats exported more oxygen overall, and the balance inside the mat shifted in ways that buried more leftover carbon. That buried carbon can’t react with oxygen later, which helps oxygen build up in air and water. Think of it like saving money: the longer the day, the more “extra oxygen” makes it into the savings account.
Two big oxygen leaps in Earth’s past—and why they matter
When scientists plugged the mat results into big-scale models, they saw something exciting. The timing of longer days lined up with major boosts in oxygen: the Great Oxidation Event, very early in Earth history, and a later lift called the Neoproterozoic Oxygenation Event.
The model doesn’t say day length is the only reason for these jumps—volcanoes, nutrients, and plate tectonics also matter—but it shows that a slower spin could be a powerful helper. In short, the length of the day can change how much oxygen tiny coastal ecosystems leak out, which adds up across Earth and across deep time.
What this means for you, your lungs, and future science
For your daily life, the change is microscopic. We’re talking about milliseconds added to the day each century—far too small for your watch. But for Earth science, this is a big clue. It tells us that physics you can learn in middle school (tides, light, diffusion) can shape the chemistry of a whole planet. It also gives astronomers a new trick: if we find a world with signs of microbial mats and a certain day length, we might estimate how easily oxygen could build up there.
That matters when we’re deciding which planets near distant stars deserve a closer look for life. This story ties together the dance of the Moon and Earth, the rise of oxygen that animals (and you) depend on, and the daily schedule of microbes the size of dust.
So remember, next time your wristwatch goes off by half a second, blame Earth’s rotation, not the brand!