Cyanobacteria: The ultimate sacrifice

Abhimanyu Kapoor
3 min readJul 5, 2020


Photo by CDC on Unsplash

Could you imagine that an organism almost got extinct due to its own actions but at the same time paved the way for the evolution of complex organisms like us?

The organism which I am talking about is a bacteria, it is the mighty Cyanobacteria also known as blue-green algae.

Long ago, there was no free oxygen in the earth’s atmosphere but there was plenty of carbon dioxide (almost 200 times more then today) and other gases like hydrogen sulfide, methane and nitrogen. Oxygen only existed in combined forms such as in water or by forming oxides with substances.

The organisms living at that time were simple, single celled microorganisms. These organisms only had genetic material which was not even enclosed by a nucleus because of which they were called Prokaryotic organisms. These organisms obtained energy through anaerobic respiration (respiration without oxygen) and they used molecules of any substance they found in the ocean as a source of food. Cyanobacteria, one such organism formed a majority of these microorganisms.

Some Cyanobacteria came to the surface of the ocean and got exposed to sunlight. On the surface there was: -water, sunlight, and carbon dioxide. The Cyanobacteria adapted in such a way that it used these three ingredients to carry out photosynthesis. In the process they made glucose which they used as a source of food. Carrying out photosynthesis for glucose was a better alternative to searching for single molecules of food and they were happy.

Their happiness did not last long as: — Little did they realize what destruction they were about to unleash.

In the process of photosynthesis, oxygen was also released into the earth’s atmosphere. Initially, the oxygen was getting used up in reactions with substances on the earth’s surface and making compounds like the iron forming iron ore.

The number of Cyanobacteria increased exponentially. Now they started releasing a lot of oxygen into the atmosphere and oxygen started to exist in a free state in the Earth’s atmosphere. Since oxygen was toxic to anaerobic organisms a mass extinction occurred, in which most of the Cyanobacteria faced extinction along other microorganisms. This is known by scientists as the great oxygenation event.

At the same time the organisms that survived, adapted to the presence of oxygen and started aerobically respiring (respiration in the presence of oxygen). Aerobic respiration gave much more energy to the organism than anaerobic respiration. For each molecule of glucose aerobic respiration gave 19 times more energy in comparison to anaerobic respiration. The organisms developed into complex life forms like plants and animals using up the extra energy.

Cyanobacteria paved way for the present day animal and plant life forms.

So let us all thank Cyanobacteria for the great sacrifice they made because of which we exist.

If you liked this story you can read an article about the reality of coronavirus below.



Abhimanyu Kapoor

A student wanting to express the colours of life through poems, articles and stories.