Terminology - geochronology . [3] The adjectives are...

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Terminology Units in geochronology and stratigraphy [2] Segments of rock ( strata ) in chronostratigraphy Periods of time in geochronology Notes Eonothem Eon 4 total, half a billion years or more Erathem Era 10 total, several hundred million years System Period Series Epoch tens of millions of years Stage Age millions of years Chronozone Chron smaller than an age/stage, not used by the ICS timescale The largest defined unit of time is the supereon , composed of eons . Eons are divided into eras , which are in turn divided into periods , epochs and ages . The terms eonothem , erathem , system , series , and stage are used to refer to the layers of rock that correspond to these periods of geologic time. Geologists qualify these units as Early, Mid, and Late when referring to time, and Lower, Middle, and Upper when referring to the corresponding rocks. For example, the Lower Jurassic Series in chronostratigraphy corresponds to the Early Jurassic Epoch in
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Unformatted text preview: geochronology . [3] The adjectives are capitalized when the subdivision is formally recognized, and lower case when not; thus "early Miocene" but "Early Jurassic." Geologic units from the same time but different parts of the world often look different and contain different fossils, so the same period was historically given different names in different locales. For example, in North America the Lower Cambrian is called the Waucoban series that is then subdivided into zones based on succession of trilobites . In East Asia and Siberia , the same unit is split into Alexian , Atdabanian , and Botomian stages. A key aspect of the work of the International Commission on Stratigraphy is to reconcile this conflicting terminology and define universal horizons that can be used around the world....
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Terminology - geochronology . [3] The adjectives are...

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