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geologic-time unit


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A subdivision of geologic time, based on the rock record of the corresponding chronostratigraphic unit. Each time unit coincides with a particular chronostratigraphic unit and, like them, time units are ranked in order of decreasing duration, each unit comprising a number of units of shorter time interval (e.g. two or more chrons comprise an age, two or more ages comprise an epoch, etc.).Geologic-time units generally bear the same name as their chronostratigraphic counterparts, but the terms ‘lower’, ‘middle’, and ‘upper’ are changed to ‘early’, ‘middle’, and ‘late’.

Chronostratigraphic Unit

Geologic-time Unit

*eonothem

*eon(longest)

*erathem

*era

*system

*period

*series

*epoch

*stage

*age

*chronozone

*chron

Subjects: Earth Sciences and Geography.


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