累代

累代（るいだい、eon, aeon）は、地質時代の区分で最大のもので冥王代、太古代、原生代、顕生代の四つの累代がある。例えば顕生代（顕生累代）は化石になりうる硬い殻を持った生物の豊富な時代を統括する。英名はコイネー・ギリシャ語の単語アイオーン（αἰών）に由来する。
累代は複数の代（era）からなり、その代は紀（period）からなり、紀は世（epoch）で構成される。現在の我々の時代は顕生代の新生代第四紀完新世に当たる。以前は顕生代の他に隠生代（先カンブリア時代）しか累代は考えられていなかった。近年になり、冥王代・太古代・原生代に分けられるようになった。
累代・代・紀の地質学的タイムスケールは以下の通り：
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
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

**参考文献**

**関連項目**
 地質時代

**外部リンク ==