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2500 Mya
The great oxygenation event

The increase in Oxygen was not just a simple matter. In some ways it led to possibly the greatest mass extinction the Earth has experienced. Initially, Bacteria were mainly around volcanic vents at the bottom of the oceans. Both Acid and Alkaline waters emitted from the vents were hosts to bacterial biota where they were dependent upon minerals for their metabolic functions, interacting with the minerals from the vents and producing Sulphur, Manganese, Iron Pyrite and Iron.

Thus set up a cyclic regie, whereby iron was combined with oxygen to produce Iron Oxide - rust, which then sank to the bottom of the seas producing red stained deposits. This oxygen killed off the vast majority of the bacteria, so there was the potential for ‘normal’ processes to deposit sands and muds. The bacteria then built up again and started to oxidise the iron again and produced the red rusty deposits again, and the cycle continued. This repetition of red layers and dark muds or siliceous layers can be seen in many areas and are known as Banded Iron Formations (BIFs).

Bacteria evolved to use sunlight and water to generate the energy they needed; the process depended on green pigments in their bodies. It was the first evidence of Photosynthesis. It used water and Carbon Dioxide to produce energy. The major waste product from this process was oxygen. There was a major problem here as Oxygen, a very powerful element that easily combines with many other chemicals was poisonous to all the bacteria existing at the time, both photosynthesizing and non-photosynthetic.

The photosynthetic bacteria then evolved to withstand the action of oxygen and could survive their own waste product. This, inevitably led to a massive increase in the amount of oxygen throughout the oceans. The cycles that produced the BIFs was not necessary and all the dissolved Iron in the oceans was precipitated out. This gave rise to the massive ‘Red beds’ that provide the iron that we mine today.

When all the Iron dissolved in the oceans had been oxidized, the oxygen was released into the atmosphere. At the time one of the main constituents of the atmosphere was methane CH4 This readily combine with Oxygen to produce Carbon dioxide, which was consumed by the bacteria. Both these gases are good insulators and kept the global temperatures up. With the removal of – especially – methane, global temperatures plummeted and what we know as the Huronian Ice Age began. It is called that as it was first discovered in rocks along the shore of Lake Huron. The entire Earth was covered in ice.

The increase in Oxygen was not just a simple matter. In some ways it led to possibly the greatest mass extinction the Earth has experienced. Initially, Bacteria were mainly around volcanic vents at the bottom of the oceans. Both Acid and Alkaline waters emitted from the vents were hosts to bacterial biota where they were dependent upon minerals for their metabolic functions, interacting with the minerals from the vents and producing Sulphur, Manganese, Iron Pyrite and Iron.

All that survived may have been confined to a few small, ice-free areas, perhaps warm oases kept capable of supporting life by subsea volcanics. It is from these few survivors that pretty much all life has evolved subsequently.

Very close……

2500 Mya The great oxygenation event

Further reading:

2500 Mya
The great oxygenation event