Aeon

An aeon or a Äonothem (English eon or eonothem ) is the name given to the highest-ranking unit in the subdivision of the Earth's history. In the geochronology is called eons in the chronostratigraphy of Äonothemen ( see box).

Eons or Äonotheme always include several hundred million to well over a billion years. In the Earth four eons and Äonotheme be distinguished: Hadean, Archean, Proterozoic and Phanerozoic.

Definition

The Äonothem up in the hierarchy of chronostratigraphic units of the earth's the highest rank represents the corresponding geochronologic period is called Aeon. In the elderly and in the popular scientific literature " eon " and " Äonothem " are often used interchangeably, the term " aeon " happens more frequently.

The boundaries of chronostratigraphic units are bounded by isochronous ( simultaneous ) stratigraphic surfaces that are defined by stratigraphic or biostratigraphic marker, not by absolute age. On the hierarchy level of the Äonotheme but this is only the Phanerozoic the case. The lower limit thereof is defined by a chronostratigraphic GSSP. The other Äonotheme be absolutely dated and are therefore identical to the eons.

The four aeons or Äonotheme

The approximate time in millions of years = Ma correspond to the state in 2008.

Hadean, Archean and Proterozoic are collectively referred to as the Precambrian.

The boundary of the Proterozoic / Archean is only absolutely committed at the moment to 2500 Ma. However, this limit should be defined chronostratigraphic in the future by a GSSP. The limit of Archean / Hadean and the base of Hadaikums have so far been established only approximately.

An annotated table of the ages and their subdivisions can be found in Article Geologic time scale.

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