Era (geology)

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Corresponding units
in chronostratigraphy and
Chronostratigraphy geochronology
Aeonothem aeon
Arathem era
system period
series epoch
step Age

An arethem is a unit that is used for the chronostratigraphic subdivision of the history of the earth . The corresponding unit of time in geochronology is an era . It usually covers periods of several hundred million years.


The arena theme is the second highest unit in the hierarchy of chronostratigraphic units in the history of the earth. In geochronology , this corresponds to a period of time called an era. The terms “aera” and “era” are frequently used as synonyms in older and popular scientific literature, but only partially correctly . The term era occurs much more frequently. The boundaries of chronostratigraphic units are delimited by isochronous (contemporaneous) stratigraphic areas, which are defined by chronostratigraphic markers, not by absolute age. However, only the three most recent eras are chronostratigraphically defined, the limits of the other eras are dated by absolute age. This means that only the ara themes older than the Paleozoic Era are also defined to be the same as the corresponding eras. The International Commission for Stratigraphy is striving to define the pre-Paleozoic eras chronostratigraphically.

The duration of an era is not defined per se, but rather according to the historical context. With only one exception, eras always span more than 100 million years, often several hundred million years. In the Proterozoic and Archaean they were established at almost regular intervals by resolution of the International Commission for Stratigraphy.

Structure of an arena or an era

An era theme or an era are subdivided into an indefinite number of systems (chronostratigraphic) or into periods (geochronological). For example, the Paleozoic Arathem is divided into six systems, the Mesozoic Arathem only into three systems. The ara-themes of the Hadaikum are not further subdivided into systems. Several aeon themes or eras form an aeon theme or an aeon.

Division of the earth's history into aeon themes or aeons and aeon themes or eras

Currently, the history of the earth is divided into four aeon themes or aeons and a total of ten aeon themes or eras:

Aeonothem Arathem
Phanerozoic Cenozoic
Proterozoic Neoproterozoic
Archean Neo-Archean

An annotated table of the aeon themes / aeons, aera themes / eras and their subdivisions can be found in the article Geological timescale .

Individual evidence

  1. Overview of the Global Boundary Stratotype Sections and Points (GSSP's) of the International Commission on Stratigraphy ( Memento from June 9, 2007 in the Internet Archive )


  • Felix Gradstein, Jim Ogg, Jim & Alan Smith: A Geologic timescale . Cambridge University Press 2005, ISBN 9780521786737
  • North American Commission on Stratigraphic Nomenclature (NACSN): North American stratigraphic code . American Association of Petroleum Geologists Bulletin, 89: 1547-1591, Tulsa, Oklahoma 1983, ISSN  0149-1423 PDF
  • Fritz F. Steininger and Werner E. Piller: Recommendations (guidelines) for handling the stratigraphic nomenclature . Courier Forschungsinstitut Senckenberg, 209: 1–19, Frankfurt am Main 1999, ZDB -ID 530500-7 .