Great Oxidation Event কী?

The Great Oxidation Event is the interval, from about $2.46$ to about $2.06$ billion years ago, during which free oxygen first built up in the Earth’s atmosphere and shallow seas, reaching perhaps a tenth of its present level.

The Great Oxidation Event (GOE) is the interval, from about 2.4–2.3 to about $2.1\,\mathrm{Ga}$, during which oxygen first accumulated durably in the atmosphere and the shallow ocean, rising from less than a millionth of its present level to perhaps a tenth.