Geological history of oxygen

The geological history of oxygen’s abundance and distribution on Earth, shaped by biological production, chemical sinks, and changes in the atmosphere and oceans.

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Oxygenic photosynthesis: Photosynthesis that uses water as an electron donor and releases molecular oxygen. It supplied the oxygen whose accumulation reshaped Earth’s surface environments.
Archean: The eon from about 4.0 to 2.5 billion years ago, when Earth’s early crust and life developed. Its low-oxygen atmosphere preceded the first major oxygenation.
Ozone layer: A region of the stratosphere where ozone absorbs much of the Sun’s ultraviolet radiation. Atmospheric oxygen enabled ozone formation, reducing ultraviolet exposure at the surface.
Oxygen overshoot: A proposed interval when atmospheric oxygen rose substantially before declining or stabilizing. It could explain evidence for oxygen pulses before sustained oxygenation.
Redox reaction: A chemical reaction in which electrons move between substances, changing their oxidation states. Oxygen’s production and removal are governed by coupled oxidation and reduction.
Iron formations: Layered sedimentary rocks containing iron oxides and silica, commonly formed in ancient oceans. Dissolved iron consumed oxygen and left a geological record of early ocean chemistry.
Paleoproterozoic: The geological era from 2.5 to 1.6 billion years ago, encompassing the Great Oxidation Event. The first major atmospheric oxygen rise occurred during this era.
Eukaryogenesis: The evolutionary origin of eukaryotic cells, which contain a nucleus and internal membrane-bound structures. Oxygen availability may have supported the energetic demands of complex cells.
Shuram excursion: A large negative carbon-isotope excursion recorded in some Ediacaran sedimentary rocks. Its cause and relationship to ocean oxygenation remain debated.
Great Oxidation Event: A major rise in atmospheric oxygen about 2.4 billion years ago, after oxygen had accumulated from microbial photosynthesis. It provides the clearest named milestone for the transition to an oxygen-bearing atmosphere.