The slowing of the Earth’s rotation helped bacteria produce atmospheric oxygen

• The Earth’s rotation has gradually slowed down since its formation around 4.5 billion years ago.
• This slowing down means the days are getting longer, which helps some bacteria to produce more oxygen.
• A new study suggests that these bacteria produced enough oxygen 2 billion years ago for life to survive.

Since its formation about 4.5 billion years ago, the Earth’s rotation has gradually slowed down, and therefore its days have gradually lengthened.

While Earth’s slowdown is not noticeable on a human timescale, it is enough to produce significant changes over the eons. One of those changes, according to a new study released Monday, is perhaps the most significant of all: The lengthening of the days has increased the amount of oxygen in Earth’s atmosphere.

As Earth’s days lengthened, blue-green algae, known as cyanobacteria, which emerged and proliferated around 2.4 billion years ago could have produced more oxygen as sub -metabolic product, suggest the study authors.

“A lingering question in earth sciences has been how the Earth’s atmosphere got its oxygen and what factors were controlled when this oxygenation took place,” said Gregory Dick, a microbiologist at the University of Michigan and co-author of the study, in a press release. Release.

“Our research suggests that the speed at which the Earth rotates – in other words, the length of the day – may have had a significant effect on the pattern and timing of Earth’s oxygenation,” he said. added.

Longer days encouraged bacteria to produce more oxygen

There are two main elements in this story which, at first glance, don’t seem to have much to do with each other. The first is that the Earth’s rotation slows down. The rate of rotation of the Earth slows down because the Moon exerts a gravitational pull on the planet. As the moon moves away from Earth, it imperceptibly slows down the speed of our planet’s rotation.

Research suggests that the days of Earth are growing 1.8 milliseconds longer every century. In the childhood of our planet, days could be as short as 6 hours. About 1.4 billion years ago, days lasted only 18 hours.

The second element is known as the Great Oxidation Event – when cyanobacteria emerged in such large quantities that the Earth’s atmosphere experienced a significant increase in oxygen between 2.4 billion and 2 billion years ago. ‘years.

Without this event, scientists believe that life as we know it could not have emerged.

Researchers still don’t know why the event happened when it happened and not earlier in Earth’s history, but the new study may help connect the dots.

In the Middle Island sinkhole in Michigan’s Lake Huron, there are mats of cyanobacteria-like microbes responsible for the great oxidation event.

In these lake bed mats, purple cyanobacteria that produce oxygen through photosynthesis compete with white microbes that metabolize sulfur. At night, white microbes climb to the top of the microbial mat and munch on their sulfur. When day breaks and the sun rises high enough in the sky, the white microbes retreat and the purple cyanobacteria soar to the top.

“Now they can start photosynthesizing and producing oxygen,” study co-author Judith Klatt said in the statement. “However, it takes a few hours before they really start, there is a long lag in the morning. Cyanobacteria are more late risers than morning people, it seems.”

This means that the daytime window during which cyanobacteria can pump oxygen is very limited – and it is this fact that has caught the attention of researchers at the University of Michigan. They wondered if the change in day length over the course of Earth’s history had an impact on the photosynthesis of cyanobacteria.

“It is possible that a similar type of competition between microbes contributed to the delay in oxygen production on early Earth,” Klatt said.

To test this hypothesis, Klatt and Dick’s team performed experiments and measurements on Lake Michigan bed microbes, both in their natural environment and in the laboratory. They also created models based on their findings that linked sunlight to microbial oxygen production and microbial oxygen production to Earth’s history.

“Intuition suggests that two 12-hour days should be similar to one 24-hour day. Sunlight rises and falls twice as fast, and oxygen production follows at the same rate,” Arjun Chennu, a scientist sailor from the Leibniz Center for Tropical Marine Research in Germany and co-author of the study, said in the statement.

“But the release of oxygen from bacterial mats does not, because it is limited by the rate of molecular diffusion. This subtle decoupling of the release of oxygen from sunlight is at the heart of the mechanism,” a- he declared.

These results were incorporated into global models of oxygen levels, and the team found that the lengthening of the days was related to the increase in Earth’s oxygen – not just the great oxidation event, but also a second atmospheric oxygenation called the neoproterozoic oxygenation event which occurred between 550 and 800 million years ago.

“We show that there is a fundamental link between the length of the day and the amount of oxygen that can be released by microbes in the soil,” Chennu said. “It’s pretty exciting. In this way, we connect the dance of the molecules of the microbial mat with the dance of our planet and its moon.”