Oxygen Blue Sky and Complex Life Exist Because of a Bacteria

Super fact 72 : About three billion years ago Cyanobacteria evolved a new type of photosynthesis that used sunlight, water, and carbon dioxide to create energy, while releasing oxygen as a waste product. This transformed the atmosphere and enabled complex life by allowing aerobic respiration to evolve. This invention turned the sky blue, gave us the protective ozone layer, but also caused climate change resulting in massive extinctions.

A microscopic photo of Cyanobacteria. They look like green blobs with small nucleuses. | Oxygen Blue Sky and Complex Life Exist Because of a Bacteria
An example of a Cyanobacteria. From Wikipedia. Luke Thompson from Chisholm Lab and Nikki Watson from Whitehead, MIT, CC0, via Wikimedia Commons

Cyanobacteria, also known as blue-green algae, are bacteria capable of oxygenic photosynthesis. Between 3.4 and 2.5 billion years ago they developed a new and very effective form of photosynthesis, which took advantage of highly abundant resources, using sunlight, water, and carbon dioxide turning it into sugar and releasing oxygen as byproduct. This is referred to as the Great Oxidation Event. You can read more about this event here, here, here, here, here, or in the book Becoming Earth by Ferris Jabr.

The atmosphere prior to the Great Oxidation Event was primarily composed of volcanic gases including nitrogen, carbon dioxide, water vapor, methane and ammonia, but almost no free oxygen. The Great Oxidation Event changed all this, but it likely took at least 200 million years.

Labeled educational bacteria internal structure scheme.
Cyanobacteria vector illustration. Biological blue green algae diagram with carboxysome, thylakoid and phycobilisome parts location inside cell. Asset id: 1687712761 by VectorMine

A Microbial Great Extinction and Snowball Earth

Oxygen was a toxic gas to many early microbes forcing them to adapt or perish. In addition, the change in the atmospheres composition changed the climate, resulting in a severe global cooling referred to as Snowball Earth. This caused a great extinction, perhaps the most severe extinction in Earth’s history. It is not included among the five mass extinction events in Earth’s history because it happened very early in Earth’s history when only primitive microbial life existed and fossil evidence from that time is nearly non-existent. The definition of a mass extinction event is that at least 75% of the world’s species are lost during a short period of time – geologically speaking. This period is not clearly defined but often defined to be two million years. It is very difficult to determine whether the great extinction following the Great Oxidation Event qualifies as a mass extinction event. To read about mass extinctions click here.

Ancient Earth almost entirely covered by ice and white snow. | Oxygen Blue Sky and Complex Life Exist Because of a Bacteria
Proterozoic era in the history of the Earth. Snowball earth. Global glaciation of the Earth. Asset id: 2010272753 by Elena Kelman

The Ozone Layer and the Blue Sky

Oxygen is also responsible for formation of the ozone layer in the atmosphere. The UV radiation from the sun split oxygen molecules, which consist of two oxygen atoms, into two separate atoms of oxygen, which then reacted with another oxygen molecule to generate ozone, and oxygen molecule consisting of three oxygen atoms. Ozone acts as a natural sunscreen to prevent harmful UV radiation from reaching the earth. Therefore, oxygen not only enables land dwelling complex multicell organisms to exist by allowing aerobic respiration to evolve, but also by protecting life from too much UV radiation.

As mentioned above, the atmosphere prior to the Great Oxidation Event was primarily composed of volcanic gases and almost no free oxygen. The color of the sky was likely orange, brown. As oxygen replaced the existing gases the sky slowly turned blue. Oxygen molecules along with Nitrogen molecules scatter blue light from the sun through a process called Rayleigh scattering, making the sky appear blue.

Cyanobacteria and The Great Oxygenation Event

It should be noted that there were other geological and biological processes that were responsible for this permanent shift in the Earth’s system, including changes in the composition of volcanic emissions and chemical reactions that allowed atmospheric hydrogen to escape to space, leaving behind an excess of oxygen molecules. However, whatever the exact mix of mechanisms, cyanobacteria were undoubtedly a critical source of accumulating oxygen. It is possible that tectonic activity altered the cycling and distribution of phosphorus and other nutrients essential for cyanobacteria. To read more see the book Becoming Earth by Ferris Jabr.

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Author: thomasstigwikman

My name is Thomas Wikman. I am a software/robotics engineer with a background in physics. I am currently retired. I took early retirement. I am a dog lover, and especially a Leonberger lover, a home brewer, craft beer enthusiast, I’m learning French, and I am an avid reader. I live in Dallas, Texas, but I am originally from Sweden. I am married to Claudia, and we have three children. I have two blogs. The first feature the crazy adventures of our Leonberger Le Bronco von der Löwenhöhle as well as information on Leonbergers. The second blog, superfactful, feature information and facts I think are very interesting. With this blog I would like to create a list of facts that are accepted as true among the experts of the field and yet disputed amongst the public or highly surprising. These facts are special and in lieu of a better word I call them super-facts.

35 thoughts on “Oxygen Blue Sky and Complex Life Exist Because of a Bacteria”

  1. I had heard of Snowball Earth, but did not understand the full picture, so thanks for this info, Thomas!

    It’s good to know that despite multiple extinctions, there is still life on earth. It will continue in some form despite the damage we are doing now.

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    1. Thank you so much Audrey. Not many of microbes (other than cyanobacteria) survived the atmosphere filling up with oxygen and then the snowball earth that followed. I’ve read (but didn’t quote) that 99% of life died out. But it paved the way for complex life. We are warming the globe at a pace many times faster, even thousands of times faster than what is typical for natural warmings, but it looks like we are slowly turning things around. Hopefully, we will not destroy our grandchildren’s future.

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  6. Absolutely fascinating Thomas I was not aware of any of this…Looking forward to your review of “Becoming Earth” I suppose everything has to be aligned which is probably why other planets cannot sustain life like we do on earth …Just image if it had have been there would be lots of earths surrounding us in the solar system…

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  7. Thanks for the fascinating look at the role cyanobacteria played in creating oxygen and the ozone layer. I had not realized that the Great Oxidation event might have qualified as a mass extinction event, though it does make it sense how it might.

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    1. Thank you David. I should say that it was a very drawn out process, at least 200 million years, and the snowball earth that followed lasted a long time. Even though the scientists in the field guess that 99% of all life / microbes died out that is not known for sure, and also it took much longer than the 2 million years (or less) typically used to define a mass extinction event, so it is not counted as one of the five mass extinction events.

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  8. It’s bacteria’s world. We just live in it.

    I would love to be able to go back in time and look at some of these extreme periods in Earth’s history like the Snowball Earth or the collision that produced the Moon or the Late Heavy Bombardment. From a safe remove of course.

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  10. It’s humbling to realize that the oxygen we breathe today owes its origin to tiny cyanobacteria — quiet microbes that reshaped the world. The insight that their action affected everything from sky colour to complex life makes this article a gentle reminder of life’s fragile roots. Thank you, Thomas for sharing such an eye-opening perspective.

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    1. Thank you Debby. I missed this too until recently. I guess you have to take a college class in biology to find this out. We often miss the most fascinating things by not studying every subject. I am trying to be a suoer fact hunter.

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