Life on Earth depends on oxygen, everyone knows, but how did it come about? Is it related to the day-night rhythm of the planet? Researchers study bacteria in a lake in the United States. This is a fundamental concern for everyone, says Gregory Dick, professor of microbiology at the University of Michigan, with a blink of an eye: “What are the conditions that support life like ours?”
This question was sent to him and his colleague Judith Claude, to the Max Planck Institute of Marine Biology, in what is known as the “Ancient Earth.”
Earth formed about 4.54 billion years ago, with a margin of error of about 50 million years. Traces in rocks and fossils indicate that the first signs of life on the planet are about 3.5 billion years old (all of which are only estimates based on evidence collected to date).
As far as the life we know is biological life, it may have started after a while. Probably another billion years later, in the very depths of the oceans, microbes called “Extramobiles” thrive.
Scientists believe that the origin of life may have been facilitated when the Earth’s rotation was reduced to about 2.4 billion years ago.
The slow cycle produces longer days, which means more time for organisms to produce more light and oxygen, suggests a study published in the journal Nature Geosciences by Dick and Claude.
“Ancient Earth” at the bottom of a lake
It takes about 365 days for the earth to complete a translation around the sun. In fact, it is 365.25 days, and this extra time is responsible for some inconsistencies in the Roman calendar.
Typically, a day lasts 24 hours (on average, to simplify things), the time the planet orbits on its own axis. But scientists believe the movement was once fast, six hours a day billions of years ago.
It is not yet known how and when the earth got its oxygen. To explore this, Claude, Dick, and others developed a strategy by studying “cyanobacterial mats” on Huron Lake in the United States.
At a depth of about 23 meters, scientists are researching an area that represents the “ancient earth”: the water there is low in oxygen and full of sulfur, with all the flora and fauna of the lake. But there is a dense purple mat of cyanobacteria.
Substitution of two types of bacteria
They are one of the oldest bacteria on earth. Aquatic and photosynthetic, they need sunlight to survive. “We want to understand how oxygen was produced on early Earth and the only significant biological source of oxygen on the planet is cyanobacteria, which evolved billions of years ago,” Claude explains.
Scientists wrote in their journal, “Oxygen photosynthesis in microbes was a significant source of oxygen for the Great Oxidation Event (GOE) about 2.4 billion years ago.” According to scientists, in Huron Lake, the purple and oxygen-producing cyanobacteria must “compete” with the sulfur-antioxidant bacteria.
“From twilight to dawn, the sulfur-eating bacteria sit on the cyanobacteria and block access to sunlight. When the morning sun comes out, the sulfur-eating bacteria move downward and the cyanobacteria rise to the surface of the mat.” When the sun goes down, the cyanobacteria begin the process of photosynthesis and produce oxygen.
“However, it takes a few hours for something to happen and there is a long delay in the morning,” Claude continues. “Cyanobacteria seem to wake up too late. As a result, their time for photosynthesis is only a few hours a day.”
But as the days on Earth got longer – with longer exposure to the sun – they produced more oxygen. According to team physiologist Brian Orbick, the days when the Earth-Moon system was formed were very short, probably six hours. But then “our planet’s rotation slowed down due to the gravity of the moon and the friction of the waves,” and the days went on.
Claude believes that daylight length and oxygen in microbial mats are related to “very basic and basic” levels: in short days, there is less time for oxygen to escape from the mats.
The team includes researchers from the Leibniz Center for Tropical Marine Research in Germany and the Annis Water Resource Institute at Grand Valley State University in the United States.
They are still exploring samples collected from the bottom of the lake and are constantly monitoring local conditions to understand the regulation of oxygen production in cyanobacteria and why, in recent times, oxygen has actually formed on Earth.