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The Paleoproterozoic era is the earliest of the three Proterozoic eons. It lasted from 2.5 to 1.6 billion years ago, and saw the rise of some of the earliest life on Earth. The most notable event of this era was the Great Oxygenation Event, which saw oxygen levels in the atmosphere rise to levels that would support complex life.
This era was preceded by the Hadean eon, and followed by the Mesoproterozoic era.