The Earth formed about 4.5 billion years ago, and since then, its rotation has gradually slowed down, resulting in a steady increase in the length of the day.
While humans have not seen a slowdown in the rotation of our planet for a lifetime, over the millennia, change has taken a significant turn. According to new research, one such change is probably the most important, at least for us: the increase in day length is related to the saturation of the Earth’s atmosphere with oxygen.
Specifically, blue-green algae (or cyanobacteria) that appeared and spread about 2.4 billion years ago should have been able to produce more oxygen as a metabolic by-product with increasing day length.
“It is an immortal question in earth sciences how the earth’s atmosphere received oxygen, what factors controlled the process of oxygen enrichment. “Our research suggests that the Earth’s rotation rate, in other words, the length of the day, may have had a significant effect on the Earth’s oxygen saturation characteristics and distribution over time,” said Gregory Dick, a microbiologist at the University of Michigan.
There are two main components to this story that, at first glance, have little to do with each other. The first is that the rotation of the earth is slowing down.
The reason for the slowing of the Earth’s rotation is the gravitational influence of the Moon on our planet; As the moon gradually moves away from us, the earth’s rotation rate decreases.
We know from fossils that 1.4 billion years ago the length of the day was only 18 hours, while 70 million years ago it was an hour and a half shorter than today. Evidence indicates that the length of the day increases by 1.8 milliseconds per century.
The second component is called the Great Oxidation Event (the same oxygen catastrophe) – when so much cyanobacteria appeared that oxygen in the Earth’s atmosphere increased dramatically. Scientists think that without this event a form of life known to us could not have emerged. Consequently, although many today do not even know about cyanobacteria, the fact is that without them we would probably not be alive.
We do not yet know much about this event, including why it happened when it happened and not at another time, even in the earliest history of the earth.
Scientists working on cyanobacterial microbes have decided to study this issue. Huron Lake is home to microbial “carpets” that are thought to be similar to the cyanobacteria that caused the oxidation.
Purple cyanobacteria, which produce oxygen through photosynthesis, and white microbes, which metabolize sulfur, compete with each other in the bottom of a lake, in a microbial carpet. At night the white microbes climb to the top of the microbial carpet and begin to absorb sulfur. At dawn, when the sun rises high in the sky, white microbes retreat and are replaced by cyanobacteria.
“By this time they can already start photosynthesis and produce oxygen. However, at this point you are still a few hours away from them as there is a long interval in the morning. “Cyanobacteria are like people who like to get up late,” said Judith Clatt, a geomicrobiologist at the Max Planck Institute for Marine Biology.
This means that the time of day when cyanobacteria can produce oxygen is very limited; It was this fact that caught the attention of University of Michigan oceanographer Brian Arbick. He wondered if photosynthesis was influenced by changes in day length over the course of Earth’s history.
“It is possible that this type of competition contributed to the delay in the production of oxygen on Earth early,” explains Klatt.
To demonstrate this hypothesis, the group conducted experiments and measurements on microbes, both in the natural environment and in the laboratory. Based on the results obtained, detailed modeling studies were also performed to link sunlight to the production of oxygen by microbes, the latter to the history of the Earth.
“It is easy to understand that two days of 12 hours are equal to one day of 24 hours. “Sunlight rises and falls twice as fast, which is followed by the production of oxygen,” explains Arun Chenu, a scientist at the Leibniz Center for Tropical Marine Studies.
According to him, this is not the case with the release of oxygen by bacterial carpets because it is limited by the rate of molecular diffusion. At the heart of the mechanism is this slight separation of oxygen production from sunlight.
The results were incorporated into global models of oxygen levels, and the team found that the increase in day length was associated with an increase in the Earth’s oxygen content – not just a major oxidation event, but a second oxygen saturation event called neoproterozoic oxidation, about 550 miles ago.
“We have linked the laws of physics working on a wide variety of scales, from molecular diffusion to planetary mechanics. We have shown that there is a fundamental relationship between day length and the production of oxygen by microbes inhabiting the soil. It is very exciting. In this way, we connect the dance of molecules in microbial carpets with the orbital dance of our planet and its moon, ”Chenu said.