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Eras mapped into Eons
Eras in the Phanerozoic Eon[1][2]
Geologic Era
Span of Years
Notes:
Cenozoic
present – 065.5 (+/- 0.3) Mya
many GSSP points
Mesozoic
065.5 (+/- 0.3) Mya – 251.0 (+/- 0.4) Mya
many GSSP points
Paleozoic
251.0 (+/- 0.4) Mya – 542.0 (+/- 1.0) Mya
mostly GSSP points
Eras in the Proterozoic Eon 542.0 (+/- 1.0) Mya – 2500 Mya[1][2]
Neoproterozoic
542.0 (+/- 1.0) Mya – 1000 Mya
few GSSP points
Mesoproterozoic
1000 Mya – 1600 Mya
all GSSA points
Paleoproterozoic
1600 Mya – 2500 Mya
all GSSA points
Eras in the Archean Eon 2500 Mya – years > 3600 Mya rocks older than 2.5 Billion years – rocks older than 3.6 Billion years[1][2]
Neoarchean
2500 Mya – 2800 Mya
(only GSSA points)
Mesoarchean
2800 Mya – 3200 Mya
Paleoarchean
3200 Mya – 3600 Mya
Eoarchean
3600 Mya – 4000 Mya
Earth's crust solidifies ca 3800 Mya[3]
Note: Rocks older than ca. 2500 Mya old are rare due to tectonic activity recycling the Earth's crust.
In stratigraphy, paleontology, geology, and geobiology, an erathem is the total stratigraphic unit deposited during a certain corresponding span of time during an era in the geologic timescale.
It can therefore be used as a chronostratigraphic unit of time which delineates a large span of years – less than a geological eon, but greater than its successively smaller and more refined subdivisions (geologic periods, epochs, and geologic ages). By 3,500 million years ago (Mya) simple life had developed on earth (the oldest known microbial fossils in Australia are dated to this figure).[3] The atmosphere was a mix of noxious and poisonous gases (methane, ammonia, sulfur compounds, etc.[3] – a so-called reducing atmosphere[4] lacking much free oxygen which was bound up in compounds).
These simple organisms, cyanobacteria ruled the still cooling earth for approximately a billion years[3] and gradually transformed the atmosphere to one containing free oxygen. These changes, along with tectonic activity left chemical trails (red bed formation, etc.) and other physical clues (magnetic orientation, layer formation factors) in the rock record, and it is these changes along with the later richer fossil record which specialists use to demarcate times early in planet earth's history in various disciplines.
Erathems are not often used in practice. While they are subdivisions of eonothems and are themselves subdivided into systems, dating experts prefer the finer resolution of smaller spans of time when evaluating strata.
Erathems have the same names as their corresponding eras. The Phanerozoic eonothem can thus be divided into Cenozoic, Mesozoic, and Paleozoic erathems. Similarly, the Proterozoic eonothem is divided youngest to oldest into the Neoproterozoic, Mesoproterozoic and Paleoproterozoic erathems, and the Archean eon and eonothem are divided similarly into the Neoarchean, Mesoarchean, Paleoarchean and the Eoarchean, for which a lower (oldest) limit is undefined.[1][2]
^ abcdInternational Commission on Stratigraphy, by Gabi Ogg. "International Stratigraphic Chart" (PDF). Archived from the original (PDF) on 2008-05-29. Retrieved 2008-06-17.
^ abcdF.M. Gradstein, J.G. Ogg, A.G. Smith, et al., "A Geologic Time Scale", (2004; Cambridge University Press).
^ abcd"Rockman's Geologic Time Chart". Retrieved 2008-06-17.
In stratigraphy, paleontology, geology, and geobiology, an erathem is the total stratigraphic unit deposited during a certain corresponding span of time...
specific interval of geologic time, and only this time span. Eonothem, erathem, system, series, subseries, stage, and substage are the hierarchical chronostratigraphic...
Series, of the Paleogene Period or System, and of the Cenozoic Era or Erathem. The beginning of the Danian (and the end of the preceding Maastrichtian)...
Stratigraphy (ICS) once proposed that the Quaternary be considered a sub-era (sub-erathem) of the Neogene, with a beginning date of 2.58 Ma, namely the start of...
Cretaceous Series, the Cretaceous Period or System, and of the Mesozoic Era or Erathem. It spanned the interval from 72.1 to 66 million years ago. The Maastrichtian...
used ICS Time Scale Definition Chronological unit Era Stratigraphic unit Erathem Time span formality Formal Lower boundary definition Iridium enriched layer...
within the timelines within the rock column. Eonothems are subdivided into erathems and their smaller subdivisions within geology and paleobiology and their...
used ICS Time Scale Definition Chronological unit Era Stratigraphic unit Erathem Time span formality Formal Lower boundary definition First appearance of...
used ICS Time Scale Definition Chronological unit Era Stratigraphic unit Erathem Lower boundary definition Appearance of the Ichnofossil Treptichnus pedum...
used ICS Time Scale Definition Chronological unit Era Stratigraphic unit Erathem Time span formality Formal Lower boundary definition Ten oldest U-Pb zircon...
geochronological units Eonothem Eon 4 total, half a billion years or more Erathem Era 10 defined, several hundred million years System Period 22 defined...
used ICS Time Scale Definition Chronological unit Era Stratigraphic unit Erathem Time span formality Formal Lower boundary definition Defined Chronometrically...
geochronological units Eonothem Eon 4 total, half a billion years or more Erathem Era 10 defined, several hundred million years System Period 22 defined...
used ICS Time Scale Definition Chronological unit Era Stratigraphic unit Erathem Time span formality Formal Lower boundary definition Defined Chronometrically...
used ICS Time Scale Definition Chronological unit Era Stratigraphic unit Erathem Time span formality Formal Lower boundary definition Defined Chronometrically...
geochronological units Eonothem Eon 4 total, half a billion years or more Erathem Era 10 defined, several hundred million years System Period 22 defined...
geochronological units Eonothem Eon 4 total, half a billion years or more Erathem Era 10 defined, several hundred million years System Period 22 defined...
used ICS Time Scale Definition Chronological unit Era Stratigraphic unit Erathem Time span formality Formal Lower boundary definition Defined Chronometrically...
used ICS Time Scale Definition Chronological unit Era Stratigraphic unit Erathem Time span formality Formal Lower boundary definition Defined Chronometrically...
used ICS Time Scale Definition Chronological unit Era Stratigraphic unit Erathem Time span formality Formal Lower boundary definition Defined Chronometrically...
authors list (link) "GSSP at the base of the Phanerozoic Eonothem, Paleozoic Erathem, Cambrian System, Terreneuvian Series, and Fortunian Stage". timescalefoundation...
geochronological units Eonothem Eon 4 total, half a billion years or more Erathem Era 10 defined, several hundred million years System Period 22 defined...
for context with proportional representation of eons/eonothems and eras/erathems mentioned on this page. Currently we are in the Cenozoic (abbreviated to...
geochronological units Eonothem Eon 4 total, half a billion years or more Erathem Era 10 defined, several hundred million years System Period 22 defined...
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