There are so many things in life we take for granted. Have you ever thought about how did oxygen become available? I had not thought about it before, but recently an article I read opened up this box of questions.
Oxygen was absent from the atmosphere of earth around 4.5 billion years ago. It was just not there. The conditions were not yet mature enough for the oxygen to survive. What was it then instead? At that time, the earth had a reducing atmosphere, consisting of carbon dioxide, methane, and water vapor. Crazy difficult, yeah?! Although sunlight was evaporating the water in the atmosphere and split ito oxygen and hydrogen, the oxygen was quickly reacting with methane and stay locked away from the earths;’ crust.
One day, a microbe, Cyanobacteria changed it all. These microbes could run photosynthesis by utilizing water as a fuel source. When doing photosynthesis, these microbes extract oxygen into the air. Gradually increasing over time, oxygen was produced at a faster rate than it could react with other elements. The accumulated oxygen escaped into the atmosphere from ocean and oxygenated water. Gradually, the accumulated oxygen started escaping into the atmosphere, where it reacted with methane. As more oxygen escaped, methane was eventually displaced, and oxygen became a major component of the atmosphere. This event, known as the “Great Oxidation Event,” occurred sometime between 2.4 – 2.1 billion years ago.
Before oxygen, metabolism in living organisms would have been anaerobic, involving the use of minerals present in the ocean to generate energy. The release of oxygen by cyanobacteria has changed the atmospheric composition, brought the rise of aerobic metabolism, and, ultimately, the evolution of multicellularity.
It would not be wrong if we highlight the cyanobacteria to be the reason why we are all alive.