Eon (geology)

For the Gnostic word, see aeon. For other senses of this word, see eon (disambiguation).

In general usage, an eon (sometimes spelled aeon) is a period of time arbitrarily designated by humans. Geologists refer to an eon as the largest subdivision of time on the geologic time scale. For example, the Phanerozoic Eon, which is about 550 million years long, covers the period of time during which animals with hard shells that fossilize would have been abundant.

An eon is composed of several geologic eras, which in turn are composed of geologic periods, which are composed of geologic epochs. We are currently in the Phanerozoic Eon, the Cenozoic Era, the Neogene Period, and the Holocene epoch. Formerly, only one eon existed besides the Phanerozoic: the Precambrian. More recently, the Hadean, Archean, and Proterozoic "eras" of Precambrian time have been considered eons. The geologic timescale in terms of eons, eras, and periods looks like this:

ImageSize = width:800 height:100PlotArea = left:65 right:15 bottom:20 top:5AlignBars = justify

Colors =

  id:neogene   value:rgb(0.99215,0.8,0.54)
  id:paleogene value:rgb(1,0.7019,0)
  id:cretaceous   value:rgb(0.5,0.764,0.1098)
  id:jurassic      value:rgb(0.302,0.706,0.5) 
  id:triassic    value:rgb(0.403,0.765,0.716) 
  id:permian   value:rgb(0.404,0.776,0.867) 
  id:carboniferous     value:rgb(0.6,0.741,0.855)
  id:devonian  value:rgb(0.6,0.6,0.788)
  id:silurian  value:rgb(0.694,0.447,0.714)
  id:ordovician      value:rgb(0.976,0.506,0.651)
  id:cambrian  value:rgb(0.984,0.5,0.373)
  id:neoproterozoic    value:rgb(0.792,0.647,0.583)
  id:mesoproterozoic    value:rgb(0.867,0.761,0.533)
  id:paleoproterozoic    value:rgb(0.702,0.698,0.369)
  id:eoarchean    value:rgb(0.5,0.565,0.565)   
  id:paleoarchean    value:rgb(0.6,0.592,0.569)   
  id:mesoarchean    value:rgb(0.698,0.65,0.6)   
  id:neoarchean    value:rgb(0.796,0.804,0.784)   
  id:ediacaran     value:rgb(0.918,0.847,0.737)   
  id:cryogenian    value:rgb(0.863,0.671,0.667)
  id:tonian        value:rgb(0.796,0.643,0.424)  
  id:stratherian   value:rgb(1,1,0.8)   # light yellow
  id:calymmian     value:rgb(1,1,0.8)   # light yellow
  id:orosirian     value:rgb(1,1,0.8)   # light yellow
  id:rhyacian      value:rgb(1,1,0.8)   # light yellow
  id:siderian     value:rgb(1,1,0.8)   # light yellow
  id:ectasian      value:rgb(1,1,0.8)   # light yellow
  id:stenian      value:rgb(1,1,0.8)   # light yellow
  id:cenozoic   value:rgb(1,1,0)
  id:mesozoic   value:rgb(0.5,0.6784,0.3176)
  id:paleozoic  value:rgb(0.5,0.7098,0.835)
  id:phanerozoic value:rgb(0.7019,0.886,0.819)
  id:proterozoic value:rgb(0.8,0.85,0.568)
  id:archean   value:rgb(0.6,0.6784,0.6745)
  id:hadean value:rgb(0.4,0.4,0.4)
  id:black  value:black

id:white value:white

Period = from:-4567.17 till:0TimeAxis = orientation:horizontalScaleMajor = unit:year increment:500 start:-4500ScaleMinor = unit:year increment:100 start:-4500

Define $markred = text:"*" textcolor:red shift:(0,3) fontsize:10

PlotData= align:center textcolor:black fontsize:8 mark:(line,black) width:25 shift:(0,-5)

bar:eon

at: 0 align:right $markred

  at:   -542   align:left   $markred shift:(2,3)

from: -542 till: 0 text:Phanerozoic color:phanerozoic from:-2500 till: -542 text:Proterozoic color:proterozoic from:-3800 till: -2500 text:Archean color:archean from: start till: -3800 text:Hadean color:hadean

bar:era

from: -65.5 till: 0 text:C~z shift:(0,1.5) color:cenozoic from: -251 till: -65.5 text:Meso~zoic shift:(0,1.5) color:mesozoic from: -542 till: -251 text:Paleo~zoic shift:(0,1.5) color:paleozoic from: -1000 till: -542 text:Neoprote-~rozoic shift:(0,1.8) color:neoproterozoic from:-1600 till: -1000 text:Mesoproterozoic color:mesoproterozoic from:-2500 till: -1600 text:Paleoproterozoic color:paleoproterozoic from:-2800 till: -2500 text:Neo-~archean shift:(0,1.5) color:neoarchean from:-3200 till: -2800 text:Meso-~archean shift:(0,1.5) color:mesoarchean from:-3600 till: -3200 text:Paleo-~archean shift:(0,1.5) color:paleoarchean from:-3800 till: -3600 text:Eoar-~chean shift:(0,0.5) color:eoarchean fontsize:6 from:start till: -3800 color:white

bar:period

fontsize:6

  from:   -23.03 till:    0    color:neogene
  from:  -65.5 till:   -23.03  color:paleogene
  from: -145.5   till:  -65.5  color:cretaceous
  from: -199.6   till: -145.5  color:jurassic
  from: -251   till: -199.6    color:triassic
  from: -299   till: -251      color:permian
  from: -359.2   till: -299    color:carboniferous
  from: -416 till: -359.2      color:devonian
  from: -443.7 till: -416      color:silurian
  from: -488.3   till: -443.7  color:ordovician

from: -542 till: -488.3 color:cambrian

from: -630 till: -542 text:Ed. color:ediacaran from: -850 till: -630 text:Cryo-~genian color:cryogenian shift:(0,0.5) from: -1000 till: -850 text:Ton-~ian color:tonian shift:(0,0.5) from: -1200 till: -1000 text:Ste-~nian color:mesoproterozoic shift:(0,0.5) from: -1400 till: -1200 text:Ect-~asian color:mesoproterozoic shift:(0,0.5) from: -1600 till: -1400 text:Calym-~mian color:mesoproterozoic shift:(0,0.5) from: -1800 till: -1600 text:Stath-~erian color:paleoproterozoic shift:(0,0.5) from: -2050 till: -1800 text:Oro-~sirian color:paleoproterozoic shift:(0,0.5) from: -2300 till: -2050 text:Rhy-~acian color:paleoproterozoic shift:(0,0.5) from: -2500 till: -2300 text:Sid-~erian color:paleoproterozoic shift:(0,0.5)

  from: start  till:  -2500 color:white

The term eon has sometimes been used informally as a synonym for millennium.

References

* International Stratigraphic Chart from the International Commission on Stratigraphy
* USA National Park Service
* Washington State University
* Web Geological Time Machine

Eon (geology): Encyclopedia BETA

Contents

Eon (geology)

See also

References