Glossary of geological terms
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eon / aeon
The largest subdivision of geological time. The last 539 million years comprise the Phanerozoic Eon. See geological timescale.
epoch / epoc
A subdivision of geological time smaller than a period and larger than a stage. The rocks formed within an epoch constitute a series. See geological timescale.
era / gorgyfnod
A subdivision of geological time smaller than an eon and larger than a period. See geological timescale.