Since the Earth was formed about 4.5 billion years ago, its rotation has been gradually slowing down. As a consequence, the length of days is increasing. Although this slowdown is imperceptible on the scale of a single human life, over billions of years it has caused significant changes. One of these changes is the oxygenation of the atmosphere, which significantly affected the development of life.

About 2.4 billion years ago, blue-green algae (cyanobacteria) began actively reproducing, generating oxygen as a byproduct of photosynthesis. The 2021 study suggests that the lengthening days have created favorable conditions for this process. Microbiologist Gregory Dick of the University of Michigan notes: “The speed of the Earth’s rotation — or the length of the day — may have influenced the timing and pattern of oxygenation of the atmosphere.”
The reason for the slowdown in rotation is gravitational interaction with the Moon, which is gradually moving away from our planet. According to the data, 1.4 billion years ago, a day lasted only 18 hours. Over the past 70 million years, the length of the day has increased by 30 minutes. The Earth is thought to gain 1.8 milliseconds per century.
Oxidation event
Another key event was the Great Oxidation Event, when cyanobacteria increased the oxygen content of the atmosphere to levels sufficient to support more complex life. This process was extremely important for the formation of the modern biosphere. Scientists speculate that competition between microbes may have slowed this process. For example, in the microbial mats of Lake Huron in Canada, purple cyanobacteria produce oxygen during the day while white bacteria consume sulfur at night, thus the competition for resources occurs.
Geomicrobiologist Judith Klatt explains that cyanobacteria require several hours after sunrise to begin photosynthesis. This limits the amount of time they can produce oxygen. Scientist Brian Arbic of the University of Michigan has observed that lengthening days in the past may have increased the efficiency of photosynthesis and thus oxygen production.
The researchers conducted experiments, modeling and microbial analysis to find out the relationship between day length and atmospheric oxygenation. They found that increased day length contributed to both the Great Oxidation Event and the Neoproterozoic Oxidation Event, which occurred 550-800 million years ago.
Impact of lengthened days on evolution
Scientist Arjun Chennu notes that oxygen release by bacteria is limited by the rate of molecular diffusion. This mechanism helps explain how physical processes, such as the planet’s slowing rotation, may have affected the evolution of life on Earth.
Thus, the lengthening of the days played an important role in oxygenating the atmosphere and shaping the conditions that allowed the emergence of modern life. Researchers continue to study this process, combining insights from planetary mechanics, microbiology and geochemistry.
Earlier we covered what would happen when the Earth’s core cools.
According to sciencealert.com