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Hadean | Archean | Proterozoic | Phanerozoic
English: The Archean (also spelled Archaean, formerly called the Archaeozoic, also spelled Archeozoic) is a geologic eon before the Proterozoic, ending 2500 Ma (million years ago). Instead of being based on stratigraphy, this date is defined chronometrically. The lower boundary (starting point) has not been officially recognized by the International Commission on Stratigraphy, but it is usually set to 3800 Ma at the end of the Hadean eon.
日本語: 始生代