Era (geology)

Short description: Large time span consisting of smaller time spans

An era, in geology, is a subdivision of geologic time that divides an eon into smaller units of time.[1] The Phanerozoic Eon is divided into three such time frames: the Paleozoic, Mesozoic, and Cenozoic (meaning "old life", "middle life" and "recent life") that represent the major stages in the macroscopic fossil record. These eras are separated by catastrophic extinction boundaries: the P-T boundary between the Paleozoic and the Mesozoic, and the K-Pg boundary between the Mesozoic and the Cenozoic.[2] There is evidence that catastrophic meteorite impacts played a role in demarcating the differences between the eras.

The Hadean, Archean and Proterozoic eons were as a whole formerly called the Precambrian. This covered the four billion years of Earth history prior to the appearance of hard-shelled animals. More recently, however, the Archean and Proterozoic eons have been subdivided into eras of their own.

Geologic eras are further subdivided into geologic periods, although the Archean eras have yet to be subdivided in this way.[3]

## List of geological eras in Earth's history

Eon | Era | Time frame

|
|

Phanerozoic | Cenozoic | 66 million years ago to present
Mesozoic | 251.902 to 66 million years ago
Paleozoic | 541 to 251.902 million years ago
Proterozoic | Neoproterozoic | 1,000 to 541 million years ago
Mesoproterozoic | 1,600 to 1,000 million years ago
Paleoproterozoic | 2,500 to 1,600 million years ago
Archean | Neoarchean | 2,800 to 2,500 million years ago
Mesoarchean | 3,200 to 2,800 million years ago
Paleoarchean | 3,600 to 3,200 million years ago
Eoarchean | 4,000 to 3,600 million years ago
Hadean | not officially divided into eras | Formation of Earth to 4,000 million years ago

## See also

* Erathem
* Geologic time scale
* Geon (geology)

## References

1. ↑ "Chapter 9. Chronostratigraphic units". International Commission on Stratigraphy. http://www.stratigraphy.org/upload/bak/chron.htm.
2. ↑ Erwin D.H. (1994). "The Permo–Triassic Extinction". Nature 367 (6460): 231–236. doi:10.1038/367231a0. https://www.cornellcollege.edu/geology/courses/Greenstein/paleo/Permo_Tr.pdf.
3. ↑ International Commission on Stratigraphy. "International Chronostratigraphic Chart v2018/07". http://www.stratigraphy.org/ICSchart/ChronostratChart2018-07.pdf.

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Chronology

Key topics|

* Archaeology
* Astronomy
* Geology
* History
* Big History
* Paleontology
* Time

* Periods
* Eras
* Epochs

| Calendar eras|

* Human Era
* Ab urbe condita
* Anno Domini / Common Era
* Anno Mundi
* Byzantine era
* Seleucid era
* Spanish era
* Before Present
* Hijri
* Egyptian
* Sothic cycle
* Hindu units of time (Yuga)
* Mesoamerican
* Long Count
* Short Count
* Tzolk'in
* Haab'

|

Regnal year|

* Canon of Kings
* Lists of kings
* Limmu

Era names|

* Chinese
* Japanese
* Korean
* Vietnamese

Calendars|

| Pre-Julian / Julian|

* Pre-Julian Roman
* Original Julian
* Proleptic Julian
* Revised Julian

|

Gregorian|

* Gregorian
* Proleptic Gregorian
* Old Style and New Style dates
* Adoption of the Gregorian calendar
* Dual dating

Astronomical|

* Lunisolar
* Solar
* Lunar
* Astronomical year numbering

Others|

* Chinese sexagenary cycle
* Geologic Calendar
* Hebrew
* Iranian
* Islamic
* ISO week date
* Mesoamerican
* Maya
* Aztec
* Winter count (Plains Indians)

Astronomic time|

* Cosmic Calendar
* Ephemeris
* Galactic year
* Metonic cycle
* Milankovitch cycles

Geologic time|

| Concepts|

* Deep time
* Geological history of Earth
* Geological time units

|

Standards|

* Global Standard Stratigraphic Age (GSSA)
* Global Boundary Stratotype Section and Point (GSSP)

Methods|

* Chronostratigraphy
* Geochronology
* Isotope geochemistry
* Law of superposition
* Luminescence dating
* Samarium–neodymium dating

Chronological
dating|

| Absolute dating|

* Amino acid racemisation
* Archaeomagnetic dating
* Dendrochronology
* Ice core
* Incremental dating
* Lichenometry
* Paleomagnetism
* Radiometric dating
* Radiocarbon
* Uranium–lead
* Potassium–argon
* Tephrochronology
* Luminescence dating
* Thermoluminescence dating

|

Relative dating|

* Fluorine absorption
* Nitrogen dating
* Obsidian hydration
* Seriation
* Stratigraphy

Genetic methods|

* Molecular clock

Linguistic methods|

* Glottochronology

Related topics|

* Chronicle
* New Chronology
* Synchronoptic view
* Timeline
* Year zero
* Circa
* Floruit
* Terminus post quem
* ASPRO chronology

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