The geologic time scale

1. TheGeologicTimeScale
GTS:
The geologictime scale (GTS)isa system ofchronologicaldating thatrelates
geologicalstrata (stratigraphy)to time,and is used by geologists,paleontologists,
and otherEarth scientists to describe the timing and relationshipsofeventsthathave
occurred during Earth'shistory.Thetablesofgeologictime spans,presentedhere,
agree with the nomenclature,datesand standard colorcodessetforth by the
InternationalCommission onStratigraphy(ICS).
This clock representation shows some of the major units of geological time and definitive events of Earth
history. The Hadean eon represents the time before fossil record of life on Earth; its upper boundary is now
regarded as 4.0 Ga (billion years ago).[1]
Other subdivisions reflect the evolution of life;
the Archean and Proterozoicare both eons, the Palaeozoic, Mesozoic and Cenozoic are eras of

2. the Phanerozoic eon. The three million year Quaternary period, the time of recognizable humans, is too
small to be visible at this scale.
Terminology:
In thegeologicaltimescale,thelargestdefinedunitoftimeis theeon,whichisfurther
divided successively into eras, periods,epochs,and stages. Overlaid on this general
pattern developedbygeologistsisacomplementary mappingby paleontologistswho
have defined a system of faunal stagesof varying lengths, based on changes in the
observedfossilassemblages.In many cases, such faunal stageshave been adopted in
building the geologicnomenclature,thoughin generalthere are far more recognized
faunal stages than defined geologic time units.
Geologists tend to talk in terms of Upper/Late, Lower/Early, and Middle parts of
periods and other units—for example, "Upper Jurassic", "Middle Cambrian".
Because geologic units occurring at the same time but from different parts of the
world can often look differentand contain differentfossils,there are many examples
where the same periodwashistorically givendifferentnamesin differentlocales.For
example, in North America the Early Cambrian is referred to as the Waucoban
series,which is then subdivided into zonesbased on trilobites.The same time span is
split into Tommotian,Atdabanian,andBotomian stagesin EastAsiaand Siberia.Itis
a key aspectofthe work oftheInternationalCommissiononstratigraphy to reconcile
thisconflictingterminologyanddefineuniversalhorizonsthatcan beusedaroundthe
world.
Historyofthetimescale:
Nicholas Steno laid down the principles underlying geologictime scales in the late
seventeenthcentury.Stenoarguedthatrocklayers(strata) arelaid downinsuccession,
and that each represents a “slice” of time. He also formulated the principle of
superposition,which statesthatany given stratum is probably olderthan those above
it and younger than those below it.
Steno's principles were simple, but applying them to real rocks proved complex.
During the eighteenth century, geologistscame to realize that: 1) Sequencesofstrata
were often eroded, distorted, tilted, or even inverted after deposition; 2) strata laid
down at the same time in differentareas could have entirely different appearances;
and 3) the strata of any given area represented only part of the Earth's long history.
The first serious attempts to formulate a geologicaltime scale that could be applied
anywhere on Earth tookplace in the late eighteenth century.The mostinfluential of
those early attempts (championed by Abraham Werner, among others) divided the
rocksoftheEarth'scrustinto fourtypes:primary,secondary,tertiary,andquaternary.
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"remainedin use as namesof geological
periods well into the twentieth century.

3. The identification of strata by the fossils they contained, pioneered by William
Smith,Georges Cuvier, and Alexandre Brogniart in the early nineteenth century,
enabled geologiststo divide Earth history more finely and precisely.It also enabled
them to correlate strata across national(or even continental)boundaries.Iftwo strata
(however distant in space or different in composition) contained the same fossils,
chanceswere goodthatthey had beenlaid downatthe same time.Detailed studiesof
the strata and fossils ofEurope producedbetween 1820 and1850 formedthe 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 forthe same setofstrata. The "Permian,"thoughdefinedusingstrata
in Russia, was delineated and named by British geologist Roderick Murchison.
British geologistswere also responsible forthe grouping ofperiodsinto erasand the
subdivision of the Tertiary and Quaternary periods into epochs.
When William Smith and Sir Charles Lyell first recognized that rock strata
representedsuccessive time periods,there was no way to determine whattime scale
they represented. Young earth creationists proposed dates of only a few thousand
years, while others suggested large (and even infinite) ages. For over one hundred
years,theageofthe Earth andoftherockstrata was thesubjectofconsiderabledebate
untiladvancesin the latter partof the twentieth century allowed radioactivedating to
provide relatively firm dates to geologichorizons. In the interveningcentury and a
half, geologists and paleontologists constructed time scales based solely on the
relative positions of different strata and fossils.
In 1977, the GlobalCommission onStratigraphy(now theInternationalCommission)
started an effortto define globalreferences(GlobalBoundary Stratotype Section and
Points)forgeologicperiods and faunalstages.Theirmostrecentwork isdescribedin
the 2004 geologic time scale of Gradstein, Ogg, and Smith (2005), and used as the
foundation ofthetable onthispage.The tablesofgeologicperiodspresentedhere are
in accordance with the dates and nomenclature proposed by the International
Commission on Stratigraphy,and uses the standard color codesof the United States
Geological Survey.

4. ATimeLinefortheGeologicalSciences
Dividing Earth History into Time Intervals:
Geologistshave dividedEarth'shistory into aseriesoftime intervals.These time
intervalsare notequalin length like the hoursin aday.Instead the time intervalsare
variable in length.Thisisbecause geologictime isdivided usingsignificantevents
in the history ofthe Earth.
ExamplesofBoundary"Events"
Forexample,the boundary betweenthe Permian and Triassicis marked by aglobal
extinction in which alarge percentage ofEarth'splantand animalspecieswere
eliminated.Anotherexampleis the boundary between thePrecambrian andthe
Paleozoic,which ismarked by the firstappearance ofanimals with hard parts.
Eons:
Eonsare the largestintervalsof geologictime and are hundredsofmillionsofyears
in duration.In the time scale above youcan see the PhanerozoicEon isthe most
recenteon and began more than 500 million yearsago.
Eras:
Eonsare divided into smallertime intervalsknown as eras.In the time scale above
you can see thatthe Phanerozoicisdividedinto three eras: Cenozoic,Mesozoicand
Paleozoic.Very significanteventsin Earth'shistory are used to determine the
boundariesofthe eras.
eriods:
Eras are subdivided into periods. Theeventsthatboundtheperiodsare
widespread in theirextentbutare notas significantasthosewhich
bound theeras. In the time scale aboveyou can see thatthe Paleozoicis

5. subdivided intothePermian, Pennsylvanian, Mississippian, Devonian,
Silurian, Ordovician and Cambrian periods.
Epochs:
Finersubdivisionsoftime are possible,and the periodsofthe Cenozoicare
frequently subdivided intoepochs.Subdivisionofperiodsinto epochscan be
done onlyforthe mostrecentportionofthe geologictime scale.Thisis
because olderrockshave beenburieddeeply,intensely deformedand
severely modified bylong-term earth processes.Asaresult,the history
contained within theserockscannotbe asclearly interpreted.
Ourgeologictime scale wasconstructed to visually show the duration ofeach
time unit.Thiswas done by making alineartime line on the leftside ofthe
time columns.Thickerunitssuch asthe Proterozoicwere longerin duration
than thinnerunitssuch asthe Cenozoic.
Millions of Years
Table of geologic time
Eon Era Period1
Series/
Epoch
Major Events
Start,
Million
Years
Ago2

6. Phan
e-
rozoic
Cenozoic
Neogen
e3
Holocene
End of recent glaciation and rise of
modern civilization.
0.0114
30 ±
0.0001
3 4
Pleistoce
ne
Flourishing and then extinction of many
large mammals (Pleistocene megafauna);
Creation of fully modern humans.
1.806 ±
0.005 *
Pliocene
Intensification of present ice age. Cool
and dry
climate; Australopithecines appear, many
of the existing genera of mammals, and
recent molluscs appear.
5.332 ±
0.005 *
Miocene
Moderate climate; Mountain building in
northern hemisphere;
Modern mammal and birdfamilies became
recognizable. Grasses become
ubiquitous. First hominoids appear.
23.03 ±
0.05 *
Paleoge
ne
3
Oligocen
e
Warm climate; Rapid evolution and
diversification of fauna,
especially mammals. Major evolution and
dispersal of modern types
of angiosperms.
33.9±0.
1 *
Eocene
Archaic mammals (e.g. Creodonts,
Condylarths, Uintatheres, etc) flourish and
continue to develop during the epoch.
Appearance of several "modern" mammal
families. Primitive whales diversify. First
55.8±0.
2 *

7. grasses. Reglaciation of Antarctica; start
of current ice age.
Paleocen
e
Climate tropical.
Modern plants; Mammals diversify into a
number of primitive lineages following the
extinction of the dinosaurs. First large
mammals (up to bear or small hippo size).
65.5±0.
3 *
Mesozoic
Cretace
ous
Upper/La
te
Flowering plants appear, along with new
types of insects. More modern teleost fish
begin to appear. Ammonites, belemnites,
rudists, echinoids and sponges all
common. Many new types
of dinosaurs (e.g. Tyrannosaurs,
Titanosaurs, duck bills, and horned
dinosaurs) evolve on land, as do modern
crocodilians; and mosasaurs and
modern sharks appear in the sea.
Primitive birds gradually replace
pterosaurs.
Monotremes, marsupials and placental m
ammals appear. Break up of Gondwana.
99.6±0.
9 *
Lower/Ea
rly
145.5 ±
4.0
Jurassic
Upper/La
te
Gymnosperms (especially conifers,
Bennettitales, cycads) and ferns common.
Many types of dinosaurs, such as
sauropods, carnosaurs, and stegosaurs.
Mammals common, but small.
First birds and
lizards. Ichthyosaurs and plesiosaurs dive
rse. Bivalves, ammonites, and belemnites
abundant. Echinoids very common,
161.2 ±
4.0
Middle
175.6 ±
2.0 *
Lower/Ea
rly
199.6 ±
0.6

8. also crinoids, starfish, sponges, and
terebratulid and
rhynchonellid brachiopods. Breakup
of Pangea into Gondwana and Laurasia.
Triassic
Upper/La
te
Archosaurs dominant and diverse on land,
include many large forms; cynodonts
become smaller and more mammal-like.
First dinosaurs, mammals, pterosaurs,
and crocodilia. Dicrodium flora common
on land. Many large aquatic
temnospondyl
amphibians. Ichthyosaurs and nothosaurs
common in the seas. Ceratite ammonoids
extremely common. Modern corals and
teleost fish appear.
228.0 ±
2.0
Middle
245.0 ±
1.5
Lower/Ea
rly
251.0 ±
0.4 *
Paleozoic Permian
Lopingian
Landmass unites in the supercontinent
of Pangea. Synapsid reptiles become
common (Pelycosaurs and Therapsids),
parareptiles and temnospondyl
amphibians also remain common.
Carboniferous flora replaced by
gymnosperms in the middle of the
period. Beetles and flies evolve. Marine
life flourishes in the warm shallow reefs.
Productid and spiriferid brachiopods,
bivalves, foraminifera, and ammonoids all
abundant. End of Permo-carboniferous
ice age. At the end of the period, the
Permian extinction event—95% of life on
Earth becomes extinct.
260.4 ±
0.7 *
Guadalup
ian
270.6 ±
0.7 *
Cisuralia
n
299.0 ±
0.8 *

9. Carbon-
iferous5
/
Pennsyl-
vanian
Upper/La
te
Winged insects appear and are abundant,
some growing to large
size. Amphibianscommon and diverse.
First reptiles, coal forests (Lepidodendron,
Sigillaria, Calamites, Cordaites, etc), very
high atmospheric oxygen content. In the
seas, Goniatites, brachiopods, bryozoa,
bivalves, corals, etc. all common.
306.5 ±
1.0
Middle
311.7 ±
1.1
Lower/Ea
rly
318.1 ±
1.3 *
Carbon-
iferous5
/
Missis-
sippian
Upper/La
te
Large primitive trees, first
land vertebrates, brackish water and
amphibious eurypterids; rhizodonts
dominant fresh-water predators. In the
seas, primitive sharks common and very
diverse, echinoderms (especially crinoids
and blastoids) abundant, Corals, bryozoa,
and brachiopods (Productida, Spriferida,
etc) very common; Goniatites
common, trilobites and nautiloids in
decline. Glaciation in East Gondwana.
326.4 ±
1.6
Middle
345.3 ±
2.1
Lower/Ea
rly
359.2 ±
2.5 *
Devonia
n
Upper/La
te
First clubmosses and horsetails appear,
progymnosperms (first seed bearing
plants) appear, first trees (Archaeopteris).
In the sea, strophomenid and
atrypid brachiopods, rugose and tabulate
corals, and crinoids are abundant.
Goniatite ammonoids are common, and
coleoids appear. Trilobites reduced in
numbers. Ostracoderms decline; Jawed
fish (Placoderms, lobe-finned and ray-
finned fish, and early sharks) important
life in the sea. First amphibians (but still
385.3 ±
2.6 *
Middle
397.5 ±
2.7 *
Lower/Ea
rly
416.0 ±
2.8 *

10. aquatic). "Old Red Continent"
(Euramerica).
Silurian
Pridoli
First vascular land plants, millipedes and
arthropleurids, first jawed fish, as well as
many types of armoured jawless forms.
Sea-scorpions reach large size. Tabulate
and rugose
corals, brachiopods (Pentamerida,
Rhynchonellida, etc), and crinoids all
abundant; trilobites and molluscs diverse.
Graptolites not as varied.
418.7 ±
2.7 *
Ludlow
422.9 ±
2.5 *
Wenlock
428.2 ±
2.3 *
Llandove
ry
443.7 ±
1.5 *
Ordovici
an
Upper/La
te
Invertebrates very diverse and include
many new types. Early
corals, Brachiopods(Orthida,
Strophomenida, etc), bivalves,
nautiloids, trilobites, ostracods, bryozoa,
many types of echinoderms (cystoids,
crinoids, starfish, etc), branched
graptolites, and other taxa all common.
Conodonts were a group of eel-like
vertebrates characterized by multiple
pairs of bony toothplates that appear at
the start of the Ordovician. Ice age at the
end of the period. First very primitive
land plants.
460.9 ±
1.6 *
Middle
471.8 ±
1.6
Lower/Ea
rly
488.3 ±
1.7 *
Cambria
n
Furongia
n
Major diversification of life in
the Cambrian Explosion; more than half of
501.0 ±
2.0 *

11. Middle
modern animal phyla appear, along with a
number of extinct and problematic forms.
Archeocyatha abundant in the early
Cambrian. Trilobites, Priapulida, sponges,
inarticulate brachiopods, and many other
forms all common. First chordates appear.
Anomalocarids are top predators.
Edicarian animals rare, then die out.
513.0 ±
2.0
Lower/Ea
rly
542.0 ±
1.0 *
Proter
-
ozoic
6
Neo-
proterozoi
c
Ediacar
an
First multi-celled animals. Edicarian fauna
(vendobionta) flourish worldwide. Simple
trace fossils from worm-like animals. First sponges.
630
+5/-30 *
Cryogen
ian
Possible snowball Earth period, Rodinia begins to
break up.
850 7
Tonian First acritarch radiation 1000 7
Meso-
proterozoi
c
Stenian
Narrow highly metamorphic belts due to orogeny as
Rodinia formed.
1200 7
Ectasian Platform covers continue to expand. 1400 7
Calymmi
an
Platform covers expand. 1600 7
Paleo-
proterozoi
c
Statheri
an
First complex single-celled life (eukaryotes). Columbia
(supercontinent).
1800 7
Orosiria
n
The atmosphere became oxygenic. Vredefort and
Sudbury Basin asteroid impacts. Much orogeny (the
processes that occur during mountain-building).
2050 7

12. Rhyacia
n
Bushveld Formation formed. Huronian glaciation. 2300 7
Siderian Banded iron formations formed. 2500 7
Arche
an
6
Neoarche
an
Stabilization possible of most modern cratons (old, stable part of
the continental crust that has survived merging and splitting of
continents and supercontinents).mantle overturn event.
2800 7
Mesoarch
ean
First stromatolites. 3200 7
Paleoarch
ean
First known oxygen producing bacteria. 3600 7
Eoarchea
n
Simple single-celled life (prokaryote). 3800
Hade
an
6,8
Lower
Imbrian9
c.3850
Nectarian9
c.3920
Basin
groups9
4100 Ma—Oldest known rock c.4150
Cryptic9
4400 Ma—Oldest known mineral; 4570 Ma—Formation of Earth c.4570

14. Proposed Precambrian timeline
1. The ICS'sGeologicTime Scale 2012 bookwhich includesthe new approvedtime
scale also displaysa proposalto substantially revise the Precambrian time scale
to reflect importanteventssuch asthe formation ofthe Earth orthe Great
Oxidation Event,amongothers,while atthe same time maintaining mostofthe
previouschronostratigraphicnomenclature forthe pertinenttime span.[33] (See
also Period (geology)#Structure.)
2. Hadean Eon – 4600–4031MYA[contradictory]
o Chaotian Era– 4600–4404 MYA – the namealludingbothto
the mythologicalChaosand the chaoticphase ofplanet
formation[33][34][35][contradictory]
o Jack Hillsian orZirconian Era – 4404–4031 MYA – both namesallude to
the Jack Hills GreenstoneBelt whichprovided theoldestmineralgrainson
Earth,zircons[33][34]
3. Archean Eon – 4031–2420 MYA
o Paleoarchean Era– 4031–3490 MYA
 Acastan Period – 4031–3810 MYA – namedafterthe Acasta
Gneiss[33][34]
 Isuan Period – 3810–3490MYA – named afterthe IsuaGreenstone
Belt[33]
o Mesoarchean Era– 3490–2780 MYA
 Vaalbaran Period – 3490–3020 MYA– aportmanteau basedon the
namesofthe Kapvaal(SouthernAfrica)and Pilbara (Western
Australia) cratons[33]
 Pongolan Period– 3020–2780 MYA– namedafterthe Pongola
Supergroup[33]
o Neoarchean Era– 2780–2420MYA
 Methanian Period– 2780–2630 MYA– namedforthe inferred
predominance ofmethanotrophicprokaryotes[33]
 Siderian Period – 2630–2420MYA – named forthe voluminous
banded iron formationsformedwithin itsduration[33]
4. ProterozoicEon – 2420–541 MYA
o PaleoproterozoicEra– 2420–1780 MYA
 Oxygenian Period – 2420–2250 MYA– namedfordisplaying the
first evidenceforaglobaloxidizing atmosphere[33]

15.  Jatulian orEukaryian Period – 2250–2060 MYA – namesare
respectively forthe Lomagundi–Jatuliδ13C isotopicexcursionevent
spanning itsduration,and forthe (proposed)[36][37] first fossil
appearance ofeukaryotes[33]
 Columbian Period – 2060–1780 MYA– namedafterthe
supercontinent Columbia[33]
o MesoproterozoicEra– 1780–850 MYA
 Rodinian Period– 1780–850 MYA– namedafterthe
supercontinent Rodinia,stable environment[33]
o NeoproterozoicEra– 850–541 MYA
 Cryogenian Period – 850–630 MYA– namedforthe occurrence of
severalglaciations[33]
 Ediacaran Period – 630–541 MYA
5. Shown to scale:
Compare with the current official timeline, not shown to scale:
Reference:
1) GTS & Diagram1 Taken FromWikipedia……
2) Terminology & History of the time scale Taken From
http://www.newworldencyclopedia.org/entry/Geologic_time_scale
3) A Time Line for the Geological Sciences TakenFrom www.geology.com
4) Table of geologictimeTaken From
http://www.newworldencyclopedia.org/entry/Geologic_time_scale
5) ProposedPrecambriantimelineTaken From Wikipedia