N-COUNT
（地質(zhì)中的）世，紀，期
An epoch is a very long period of time in the earth's development, marked by particular physical or biological characteristics.
例句
Two main glacial epochs affected both areas during the last 100 million years of Precambrian times.
在前寒武紀的最后1億年中，兩個主要的冰川時期對兩個地區(qū)都產(chǎn)生了影響。