https://en.wikipedia.org/wiki/Great_Oxidation_Event
大氧化事件（英語：Great Oxygenation Event），也有氧化災變（英語：Oxygen Catastrophe、Oxygen Crisis）等不同稱呼，指約26億年前大氣游離氧量突然增加的過程。這些氧來自藍綠菌的光合作用，但突然增加的完整原因尚不得知，目前只有若干種假說能解釋。此事改變了地球礦物的成份，也使日後動物的出現成為可能。[2]
The Great Oxidation Event (GOE) or Great Oxygenation Event, also called the Oxygen Catastrophe, Oxygen Revolution, Oxygen Crisisor Oxygen Holocaust,[2] was a time interval during the Early Earth's Paleoproterozoic era when the Earth's atmosphere and the shallow ocean first experienced a rise in the concentration of oxygen.[3] This began approximately 2.460–2.426 Ga (billion years) ago during the Siderian period and ended approximately 2.060 Ga ago during the Rhyacian.[4] Geological, isotopic, and chemical evidence suggests that biologically produced molecular oxygen (dioxygen or O2) started to accumulate in Earth's atmosphere and changed it from a weakly reducing atmosphere practically devoid of oxygen into an oxidizing one containing abundant free oxygen,[5] with oxygen levels being as high as 10% of their present atmospheric level by the end of the GOE.[6]
The sudden injection of highly reactive free oxygen, toxic to the then-mostly anaerobic biosphere, may have caused the extinction of many organisms on Earth—mostly archaeal colonies that used retinalto utilize green-spectrum light energy and power a form of anoxygenic photosynthesis (see Purple Earth hypothesis). Although the event is inferred to have constituted a mass extinction,[7]due in part to the great difficulty in surveying microscopic organisms' abundances, and in part to the extreme age of fossil remains from that time, the Great Oxidation Event is typically not counted among conventional lists of "great extinctions", which are implicitly limited to the Phanerozoic eon. In any case, isotope geochemistry data from sulfate minerals have been interpreted to indicate a decrease in the size of the biosphere of >80% associated with changes in nutrient supplies at the end of the GOE.[8]
The GOE is inferred to have been caused by cyanobacteria that evolved porphyrin-based photosynthesis, which produces dioxygen as a byproduct. The increasing oxygen level eventually depleted the reducing capacity of ferrous compounds, hydrogen sulfide and atmospheric methane, and compounded by a global glaciation, devastated the microbial mats around the Earth's surface. The subsequent adaptation of surviving archaea via symbiogenesis with aerobic proteobacteria (which went endosymbiont and became mitochondria) may have led to the rise of eukaryotic organisms and the subsequent evolution of multicellular life-forms.[9][10][11]
