Geologic time scale

From Free net encyclopedia

The geological time scale is used by geologists and other scientists to describe the timing and relationships between events that have occurred during the history of the Earth. The table of geologic periods presented here is in accordance with the dates and nomenclature proposed by the International Commission on Stratigraphy, and uses the standard color codes of the United States Geological Survey.

Current geological evidence holds that the age of the Earth is about 4570 million years old (expressed with "Ma": " it dates from 4570 Ma"). The geological or deep time of Earth's past has been organized into various units according to events which took place in each period. Different spans of time on the time scale are usually delimited by major geological or paleontological events, such as mass extinctions. For example, the boundary between the Cretaceous period and the Palaeogene period is defined by the extinction event that marked the demise of the dinosaurs and of many marine species.

Graphical timelines

The second and third timelines are each subsections of their preceding timeline as indicated by asterisks. <timeline> 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

</timeline>

<timeline> 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: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:black  value:black
 id:white  value:white
 id:darkgreen value:rgb(0,0.35,0)

Period = from:-542 till:0 TimeAxis = orientation:horizontal ScaleMajor = unit:year increment:100 start:-500 ScaleMinor = unit:year increment:10 start:-540

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

 bar:era
 at:      0   align:right  $markgreen
 at:    -65.5 align:left   $markgreen shift:(2,3)
 from:  -65.5 till:    0   text:Cenozoic color:cenozoic
 from: -251   till:  -65.5 text:Mesozoic color:mesozoic
 from: -542   till: -251   text:Paleozoic color:paleozoic

 bar:period fontsize:8
 from: -23.03    till:  0     text:Neo-~gene shift:(0,0.5) color:neogene
 from: -65.5  till:  -23.03   text:Paleo-~gene shift:(0,0.5) color:paleogene
 from: -145.5   till:  -65.5 text:Cretaceous color:cretaceous
 from: -199.6   till: -145.5   text:Jurassic color:jurassic
 from: -251   till: -199.6   text:Triassic   color:triassic
 from: -299   till: -251   text:Permian      color:permian
 from: -359.2   till: -299   text:Carboniferous color:carboniferous
 from: -416 till: -359.2   text:Devonian        color:devonian
 from: -443.7 till: -416 text:Sil-~urian shift:(0,0.5) color:silurian
 from: -488.3   till: -443.7 text:Ordovician color:ordovician
 from: -542   till: -488.3   text:Cambrian   color:cambrian

</timeline>

<timeline> 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:cenozoic   value:rgb(1,1,0)
 id:holocene   value:rgb(1,1,0.702)
 id:pleistocene  value:rgb(1,0.922,0.384)
 id:pliocene     value:rgb(1,0.922,0.675)
 id:miocene      value:rgb(1,0.871,0)
 id:oligocene    value:rgb(0.918,0.776,0.447)
 id:eocene       value:rgb(0.918,0.678,0.263)
 id:paleocene    value:rgb(0.92,0.576,0.005)
 id:black  value:black
 id:white  value:white
 id:darkgreen value:rgb(0,0.35,0)

Period = from:-65.5 till:0 TimeAxis = orientation:horizontal ScaleMajor = unit:year increment:10 start:-60 ScaleMinor = unit:year increment:1 start:-65

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

PlotData=

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

 bar:era
 at:     0  align:right $markgreen 
 at: start  align:left  $markgreen shift:(2,3)
 from:start  till:  0    text:Cenozoic color:cenozoic

 bar:period
 from: -23.03   till:  0   text:Neogene color:neogene
 from:start  till: -23.03   text:Paleogene color:paleogene

 bar:epoch
 from: -0.1  till:  0  color:holocene
 from: -1.806  till: -0.1  text:P color:pleistocene
 from: -5.332    till: -1.806  text:Plio-~cene shift:(0,1) color:pliocene fontsize:7
 from:-23.03    till: -5.332    text:Miocene color:miocene
 from:-33.9    till:-23.03    text:Oligocene color:oligocene
 from:-55.8    till:-33.9    text:Eocene     color:eocene
 from:start  till:-55.8    text:Paleocene    color:paleocene

</timeline>

Terminology

The largest defined unit of time is the Eon. Eons are divided into Eras, which are in turn divided into Periods, Epochs and Stages. At the same time, paleontologists define a system of faunal stages, of varying lengths, based on changes in the observed fossil assemblages. In many cases, such faunal stages have been adopted in building the geological nomenclature, though in general there are far more recognized faunal stages than defined geological time units.

Geologists tend to talk in terms of Upper/Late, Lower/Early and Middle parts of periods and other units -- e.g. "Upper Jurassic", "Middle Cambrian". Because geologic units occurring at the same time but from different parts of the world can often look different and contain different fossils, there are many examples where the same period was historically given different names in different locales. For example, in North America the Early Cambrian is referred to as the Waucoban series that is then subdivided into zones based on trilobites. The same timespan is split into Tommotian, Atdabanian and Botomian stages in East Asia and Siberia. It is a key aspect of the work of the International Commission on Stratigraphy to reconcile this conflicting terminology and define universal horizons that can be used around the world.

History of the time scale

The principles underlying geologic (geological) time scales were laid down by Nicholas Steno in the late 17th century. Steno argued that rock layers (strata) are laid down in succession, and that each represents a "slice" of time. He also formulated the principle of superposition, which states that any given stratum is probably older than those above it and younger than those below it. Steno's principles were simple; applying them to real rocks proved complex. Over the course of the 18th century geologists came to realize that: 1) Sequences of strata were often eroded, distorted, tilted, or even inverted after deposition; 2) Strata laid down at the same time in different areas could have entirely different appearances; 3) The strata of any given area represented only part of the Earth's long history.

The first serious attempts to formulate a geological time scale that could be applied anywhere on Earth took place in the late 18th century. The most influential of those early attempts (championed by Abraham Werner, among others) divided the rocks of the Earth's crust into four types: Primary, Secondary, Tertiary, and Quaternary. Each type of rock, according to the theory, formed during a specific period in Earth history. It was thus possible to speak of a "Tertiary Period" as well as of "Tertiary Rocks." Indeed, "Tertiary" and "Quaternary" remained in use as names of geological periods well into the 20th century.

The identification of strata by the fossils they contained, pioneered by William Smith, Georges Cuvier, and Alexandre Brogniart in the early 19th century, enabled geologists to divide Earth history more finely and precisely. It also enabled them to correlate strata across national (or even continental) boundaries. If two strata (however distant in space or different in composition) contained the same fossils, chances were good that they had been laid down at the same time. Detailed studies of the strata and fossils of Europe produced, between 1820 and 1850, the sequence of geological periods still used today.

British geologists dominated the process, and the names of the periods reflect that dominance. The "Cambrian," "Ordovician," and "Silurian" periods were named for ancient British tribes (and defined using stratigraphic sequences from Wales). The "Devonian" was named for the British county of Devon, and the name "Carboniferous" was simply an adaptation of "the Coal Measures," the old British geologists' term for the same set of strata. The "Permian," though defined using strata in Russia, was delineated and named by a British geologist: Roderick Murchison.

British geologists were also responsible for the grouping of periods into Eras and the subdivision of the Tertiary and Quaternary periods into epochs.

When William Smith and Sir Charles Lyell first recognized that rock strata represented successive time periods, there was no way to determine what time scale they represented. Creationists proposed dates of only a few thousand years, while others suggested large (and even infinite) ages. For over 100 years, the age of the Earth and of the rock strata was the subject of considerable debate until advances in the latter part of the 20th century allowed radioactive dating to provide relatively firm dates to geological horizons. In the intervening century and a half, geologists and paleontologists constructed time scales based solely on the relative positions of different strata and fossils.

In 1977, the Global Commission on Stratigraphy (now the International Commission) started an effort to define global references (Global Boundary Stratotype Sections and Points) for geologic periods and faunal stages. Their most recent work is described in the 2004 geologic time scale of Gradstein et al. (ISBN 0521786738), and used as the foundation of this page.

Table of geologic time

References and footnotes

<references/>

• GeoWhen Database
• International Commission on Stratigraphy Time Scale
• CHRONOS
• CHRONOS Geologic Time references
• National Museum of Natural History - Geologic Time
• BBC Interactive Time Line

See also

• Age of the Earth
• Fossils and the geological timescale
• Timeline of evolution
• Cosmological timeline
• Lunar geologic timescale
• Martian geologic timescale
• Anthropocene
• Logarithmic timeline

External links

• NASA: Geologic Time
• GSA: Geologic Time ScaleTemplate:Link FA

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