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In general usage, an eon (sometimes spelled '''aeon''') is a period of time arbitrarily designated by humans. Geologist s 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 Animal s with hard shells that Fossilize would have been abundant. An eon is composed of several . 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:100 PlotArea = left:65 right:15 bottom:20 top:5 AlignBars = 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:0 TimeAxis = orientation:horizontal ScaleMajor = unit:year increment:500 start:-4500 ScaleMinor = unit:year increment:100 start:-4500
PlotData= align:center textcolor:black fontsize:8 mark:(line,black) width:25 shift:(0,-5) bar:eon at: 0 align:right at: -542 align:left 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 Millenium . REFERENCES
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