Earth’s days are growing longer but this gradual deceleration in the planet’s spin may have played a critical role in shaping life as we know it. Scientists have found evidence that Earth’s slowing rotation, caused by the gravitational pull of the Moon, is linked to the oxygenation of the planet’s atmosphere a key factor in the emergence of complex life.
Billions of years ago, days on Earth were much shorter. Fossil records show that 1.4 billion years ago, a day lasted just 18 hours, and even 70 million years ago, days were 30 minutes shorter than they are today. This gradual slowing currently adding 1.8 milliseconds to each century is due to tidal friction as the Moon pulls slightly away from Earth.
This slowing spin coincided with a dramatic event known as the Great Oxidation Event (GOE) about 2.4 billion years ago. During this period, cyanobacteria or blue-green algae began producing significant amounts of oxygen through photosynthesis drastically altering Earth’s atmosphere and paving the way for life as we know it.
The link between Earth’s rotation and oxygenation was uncovered through experiments on microbial mats in the Middle Island Sinkhole of Lake Huron. These mats contain communities of purple cyanobacteria and white sulfur-metabolizing microbes, believed to be modern analogs of ancient microbial ecosystems.
During the day, purple cyanobacteria photosynthesize, releasing oxygen. However, researchers found that these microbes take several hours to “wake up” each morning and begin producing oxygen, shortening their window of productivity. This lag led scientists to wonder how longer days might have influenced oxygen production in Earth’s early history.
Oceanographer Brian Arbic and microbiologist Judith Klatt explored the hypothesis that Earth’s lengthening days directly impacted cyanobacteria’s oxygen output. Their findings revealed that longer days allowed these microbes more time to photosynthesize, increasing atmospheric oxygen levels over time.
Marine scientist Arjun Chennu noted, “The oxygen release from bacterial mats is not instantaneous. The physics of molecular diffusion creates a lag, meaning the microbes release more oxygen with longer exposure to sunlight.”
By modeling these processes, the researchers linked longer days not only to the GOE but also to a second major oxygenation event the Neoproterozoic Oxygenation Event 550 to 800 million years ago.
This groundbreaking study ties molecular activity to planetary mechanics. “We show a fundamental link between day length and oxygen production, bridging scales from microbes to planetary systems,” said Chennu.
The findings suggest that Earth’s gradual slowdown, driven by the Moon’s pull, set the stage for oxygen-rich conditions crucial for complex life. “This way, we link the dance of the molecules in the microbial mat to the dance of our planet and its Moon,” Chennu added.
The research provides a fascinating glimpse into how seemingly unrelated phenomena—planetary rotation and microbial activity—came together to create the breathable atmosphere we rely on today.
