Katagogian Eon

The Katagogian Eon is the third oldest eon of Espan History, and it is commonly accepted to have begun close to 4564 million (about 4.564 billion) years ago when the Odjoran systems Late Heavy Bombardment came to an end. Its during the Katagogian Eon that the Espan LUCA lived at around 4.4 BYA.

The Katagogian Eon is named after the Greek word "Katagogí" meaning Origin.

Events
Life on Espa had started out being anaerobic. Because of the thick atmosphere it did not develop much photosynthesis in these early stages, instead starting out as heterotrophic, incapable of producing their own food so instead the searched for food in their environment.

However at some point very soon after life first appeared some organisms evolved to use inorganic molecules to power chemical progresses from which they derive their energy, thus becoming autotrophic, able to produce their own food.

As these early bacteria proliferated they started changing the composition of the atmosphere, with the phototrophes releasing O2 and the chemotrophes releasing S2 into the oceans.

As the oceans begin to accumulate Oxygen and Sulfur, rusting becomame possible leaving vast iron deposits at the ocean floor as well as further acidifying the oceans. Additionally the atmospheric Sulfur dioxide concentrations dropped steadily.

Slowly but steadily the oceans began to fill up with oxygen until the point of saturation was reached by around 3.5 BYA the oceans had been completely saturated with oxygen which meant its was now being released into the atmosphere. By 2.9 BYA the oxygen levels had reached 0.3% by volume passing the Pasteur point above which facultative aerobic microorganisms and facultative anaerobes adapt from fermentation to aerobic respiration. By doing so a tipping point is reached in evolution.

Oxygen Catastrophe


This sudden appearance of atmospheric oxygen meant it could be utilized for aerobic respiration which works far more efficiently above the Pasteur point. The extreme benefits aerobic organisms now had over anaerobic microorganisms had dire results, oxygen was a poison to anaerobic life leading all the non-chemosynthetic anaerobic life to die out in the first mass extinction during which 99% of Espan lifeforms died out. This event marked the end of the Katagogian Eon and the start of the follow-up Anapnoian Eon.

Additionally to the oxygenation the higher oxygen levels have other effects on the planet, firstly the oxygen combined with Iron to start a new global phase of rusting, turning the Espan oceans brown red, but fore-mostly dropping the methane levels - The oxygen combined with the methane to form carbon dioxide and water, which do not retain heat as well as methane does - sending Espa deep into a vast ice age called the Kokkinoan Ice Age. For the planets climate to adapt to the new atmosphere 400 ma had to pass, and only by 2.5 BYA the ice would began to retreat.