Neoproterozoic oxygenation event

The Neoproterozoic Oxygenation Event (NOE), also called the "Second Great Oxidation Event", was a geologic time interval between around 850 and 540 million years ago during the Neoproterozoicera, during which the oxygen concentration in Earth's atmosphere and oceans rose significantly. Taking place after the end to the Boring Billion, a euxinic period of extremely low atmospheric oxygen spanning from the Statherianperiod of the Paleoproterozoic era to the Tonian period of the Neoproterozoic era, the atmospheric oxygen concentration rose from <0.1% PAL throughout most of the early/mid-Proterozoic to >13% PAL during the early Neoproterozoic from 900 to 815 Ma, and possibly up to ~50% PAL during the CryogenianSturtian–Marinoaninterglacial.

The NOE was the second major increase in atmospheric and oceanic oxygen concentration on Earth, after the Great Oxidation Event (GOE) of the Neoarchean-Paleoproterozoic boundary. Unlike the GOE, it is unclear whether the NOE was a synchronous, global event or a series of asynchronous, regional oxygenation intervals with unrelated causes.