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අම්ලකර නිෂ්ඨාව
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අම්ලකර නිෂ්ඨාව එසේත් නැත්නම් ඔක්සිජන් නිෂ්ඨාව (ඉංග්රීසි: Great Oxidation Event, GOE, Great Oxygenation Event, Oxygen Catastrophe, Oxygen Revolution, Oxygen Crisis, Oxygen Holocaust)[2] යනු පෘථිවි අතීතයේ Paleoproterozoic යුගය තුළ පෘථිවි වායුගෝලය සහ නොගැඹුරු සගර ප්රථම වරට ඔක්සිජන් මට්ටම ඉහළ නැගීමේ අත්දැකීම ලත් වකවානුව වෙයි.[3]
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- Stage 1 (3.85–2.45 Ga): Practically no O2 in the atmosphere. The oceans were also largely anoxic – with the possible exception of O2 in the shallow oceans.
- Stage 2 (2.45–1.85 Ga): O2 produced, rising to values of 0.02 and 0.04 atm, but absorbed in oceans and seabed rock.
- Stage 3 (1.85–0.85 Ga): O2 starts to gas out of the oceans, but is absorbed by land surfaces. No significant change in oxygen level.
- Stages 4 and 5 (0.85 Ga – present): Other O2 reservoirs filled; gas accumulates in atmosphere.[1]