The origin of oxygen: When did we start breathing? 


Earth Day is a good reason to talk about the indispensable aspects of Earth that make (human) life possible. Almost 8 billion people must coexist on Earth. We will look at the evolution of Earth as a liveable world, focussing on the atmosphere and on oxygen. And how the preservation of breathable air is very closely linked to the preservation of forests. 

Text: 2020 Kathelijne Bonne

Why is oxygen important? Humans are not above the earth. We are a part of it. That sounds like hippie talk. But it's pure science. The way our bodies work, is programmed to thrive on Earth. We're the product of four billion years of adaptation. Our metabolism depends on other organisms (which we have to eat), and on the atmosphere. 

Because we breathe oxygen. The air we breathe consists of a mixture of gases: water vapor, nitrogen, carbon dioxide and oxygen are the main ones. 

Oxygen is now indispensable, but there have been times when there was no oxygen at all.

Where does oxygen come from? 

We must go back some 2.4 billion years to find out. 

Back then, there were only single-celled creatures, mainly bacteria. The cyanobacteria or blue-green algae performed photosynthesis. That is a form of metabolism, a way to generate energy (we do that by eating and breathing). Photosynthesis involves harvesting sunlight as a source of energy and producing oxygen as a by-product. The produced oxygen is expelled into the air. 2.4 billion years ago these bacteria started to produce an enormous amount of oxygen. The oxygen content of the atmosphere increased steadily. Scientists call this event the Great Oxidation Event

Thanks to this 'new' component in the atmosphere, larger, multicellular creatures, the eukaryotes, were eventually able to develop. 

Creatures that consume oxygen came about as well. 

Oxygen consumption is also known as breathing. Animals, and ultimately humans, breathe. We extract oxygen from the atmosphere because we need it for our metabolism, to produce energy. And plants and algae give the oxygen back to the atmosphere. Indeed, there is a cycle. 

But the oxygen level fluctuates all the time, which is normal. Because the production and consumption of oxygen are not always the same. But 'normal' does mean that some species do not tolerate the small changes, and die out. And today, human activity is to blame. Today, forests are more important than ever. Planting trees is not something for sentimental hippies. One tree may be a drop in the ocean but it contributes to a liveable atmosphere and is directly linked to our physical well-being.

Furthermore, trees and forests do more than produce oxygen. They extract carbon dioxide from the atmosphere, counteracting global warming. 

In another article, we will explain that it's not just the warming we have to worry about. Now it's enough to know that creating a breathable atmosphere took millions of years and that forests play an incredibly important role in maintaining a balance in which humans can thrive. 

Have a great day and stay safe!

EarthDay even has a website! Link here.