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The Oxygenation Catastrophe

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Posted on February 5, 2015 - 5:00pm

Written by Ryan Casey

Approximately 2.3 billion years ago, Earth could have been easily mistaken for a hostile alien planet. Methane spewed into the atmosphere by constant volcanic activity, and fatal UV radiation bombarded the surface without the protection of an ozone layer. The primordial seas were blood red, a hue caused by the massive amounts of suspended iron in the water. It is beneath these red waves in which almost all life on the planet survived, most of which would require a microscope to view. Anaerobic single celled organisms were the dominant life form on earth at the time; they lived in the hostile chemical make up of the primordial sea without the need of oxygen. However just one of these single celled organisms may have caused the greatest extinction event on planet Earth: the Cyanobacteria.

What was formerly known as blue-green algae, the Cyanobacteria are actually bacteria that have the unique ability of photosynthesis. This single-celled organism had emerged only a few hundred millions years before, at a time where all other organisms relied on methods of anaerobic respiration. By creating its own energy from the sun, this bacterium was able to generate up to 16 times more energy than its counterparts, which allowed it to outcompete and explode in reproduction. This seemingly innocent organism would spell doom for most of life on the planet, as photosynthesis produced free oxygen molecules as a byproduct.

Oxygen was a poisonous element to the dominant life on the planet at the time, anaerobic bacteria. In the primordial waters, oxygen molecules would normally be absorbed by decomposing organisms or would bind with iron in the water to create rust, so oxygen did not have time to accumulate.  We can see in the geological record that 2.3 billion years ago, there was a highly unusual amount of rust being deposited on the ocean floor. We know based on this evidence that there was a huge spike of oxygen in ocean at this time. It is thought that Cyanobacteria were producing so much oxygen that it reached complete global saturation. With this, oxygen began to leave the waters and accumulate in the atmosphere, which would have profound effects on the planet.

In a relatively short amount of time, Earth went from having very little oxygen to what may be the highest levels of atmospheric oxygen it has ever had. This event had wiped out most of life on the planet to which the oxygen was poisonous. Some of these anaerobic organisms were though to have survived by burrowing into the earth where oxygen levels were survivable. What may have the biggest change is that when oxygen accumulated in the methane rich atmosphere, the concentration of this greenhouse gas dwindled, causing temperature levels to drop. They dropped so low in fact, that this oxygen event is thought to have triggered the Huronian glaciation, the longest snowball Earth period.

Over 2.3 billions years later, Cyanobacteria is still among us and continues to produce oxygen. Its byproduct is now an essential part of the earth’s atmosphere and a necessity for survival for many forms of life. This great oxygen event is credited with drastically changing the make-up of the planet, giving birth to thousands of new minerals, an environment where multi-cellular organisms could evolve, and the cooling of earth’s temperature.

If you are interested in hearing more about the early development of our planet Earth and mass extinctions, planetary scientist and director of the School of Earth and Space Exploration,  Lindy Elkins-Tanton will be speaking at ASU Gammage Auditorium on February 7th. She will join other scientists and scholars as they discuss Extinctions: Tragedy to Opportunity as a part of the Origins Project’s Great Debate series. Tickets are on sale now, and free to students with ID.

Further Reading

Holland, Heinrich D. The oxygenation of the atmosphere and oceans.
Philosophical Transactions of the Royal Society

Early Life: Oxygen the Atmosphere http://www.bbc.co.uk/science/earth/earth_timeline/first_life 

Great Oxidation Event: More oxygen through multicellularity http://www.sciencedaily.com/releases/2013/01/130117084856.htm