History of the Universe


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Great Oxygen Poisoning 2.4 bya

During the next 1.7 billion years the Earth's environment changed dramatically. Up to this point, the atmosphere has been rich in hydrogen compounds such as ammonia and methane gas. Any iron which happened to reach the Earth's surface remained shiny and bright. But everything changed when blue-green bacteria began to release oxygen.


We are familiar with the change of color from white to brown when we cut open an apple. It happens either quickly, as in a fire, or slowly, as in the case of the apple. The rusting of iron is another and even slower example.

In all cases, the atoms or molecules of the material are combining with oxygen from the atmosphere.

Oxygen atoms love to gain electrons because this lets them gain a hard outer shell. Oxygen is an electron acceptor.

It is an example of oxidation (commonly called "burning"). An oxidation is when an atom loses an electron to another atom. For example, when hydrogen combines with oxygen to make water, the hydrogen loses an electron and is oxidized.

An oxidizing agent is an atom which can easily gain electrons from other atoms. Oxygen, fluorine and ozone are examples.

Note that when one atom is oxidized, some other atom must be reduced.

Great Oxygen Poisoning

Once photosynthesis by blue-greens began to release oxygen, iron minerals in the rocks and oceans of the Earth began to combine with the oxygen and turn brown -- the world began to rust. Gradually the whole chemistry of the Earth was changed.

By 1.8 billion years ago all the minerals in the rocks and oceans had rusted. Now the oxygen made by blue-green bacteria began to collect in the atmosphere, which began to change into the air we know today. Never since has the world seen such a drastic change.

This had a terrible effect upon most bacteria. Oxygen attacked many of life's molecules, combining with them, changing their structure and giving out carbon dioxide and heat. It is the process we call burning. Burning can happen quickly, as in a fire, or slowly, as when a cut apple goes brown.

The new oxygen slowly burnt the proteins and chromosomes inside the bacteria and most of them died in the Great Oxygen Poisoning (also called the Great Oxygenation Event or the Oxygen Catastrophe) of about 2.4 bya, most but not all. Some anaerobes hid away in places where there was no oxygen, such as in the mud at the bottom of swamps. They managed to survive in any place without oxygen, and we still find them living there. These are the anaerobic bacteria which make dead matter putrefy, giving off bad smells.

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Written by Wyken Seagrave
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