Geologic time scale

The geologic time scale, proportionally represented as alog-spiralwith some major events in Earth's history. Amegaannus(Ma) represents one million (10⁶) years.

Thegeologic time scaleorgeological time scale(GTS) is a representation oftimebased on therock recordofEarth.It is a system ofchronological datingthat useschronostratigraphy(the process of relatingstratato time) andgeochronology(a scientific branch ofgeologythat aims to determine the age of rocks). It is used primarily byEarth scientists(includinggeologists,paleontologists,geophysicists,geochemists,andpaleoclimatologists) to describe the timing and relationships of events in geologic history. The time scale has been developed through the study of rock layers and the observation of their relationships and identifying features such aslithologies,paleomagneticproperties, andfossils.The definition of standardised international units of geologic time is the responsibility of theInternational Commission on Stratigraphy(ICS), a constituent body of theInternational Union of Geological Sciences(IUGS), whose primary objectiveis to precisely define global chronostratigraphic units of the International Chronostratigraphic Chart (ICC)that are used to define divisions of geologic time. The chronostratigraphic divisions are in turn used to define geochronologic units.

While some regional terms are still in use,the table of geologic time conforms to thenomenclature,ages, and colour codes set forth by the ICS.

Principles

See also:Age of Earth,History of Earth,andGeological history of Earth

The geologic time scale is a way of representingdeep timebased on events that have occurred throughoutEarth's history,a time span of about4.54 ± 0.05 Ga(4.54 billion years).It chronologically organises strata, and subsequently time, by observing fundamental changes in stratigraphy that correspond to major geological or paleontological events. For example, theCretaceous–Paleogene extinction event,marks the lower boundary of thePaleogeneSystem/Period and thus the boundary between theCretaceousand Paleogene systems/periods. For divisions prior to theCryogenian,arbitrary numeric boundary definitions (Global Standard Stratigraphic Ages,GSSAs) are used to divide geologic time. Proposals have been made to better reconcile these divisions with the rock record.

Historically, regional geologic time scales were useddue to the litho- and biostratigraphic differences around the world in time equivalent rocks. The ICS has long worked to reconcile conflicting terminology by standardising globally significant and identifiable stratigraphichorizonsthat can be used to define the lower boundaries of chronostratigraphic units. Defining chronostratigraphic units in such a manner allows for the use of global, standardised nomenclature. The ICC represents this ongoing effort.

The relative relationships of rocks for determining their chronostratigraphic positions use the overriding principles of:

• Superposition– Newer rock beds will lie on top of older rock beds unless the succession has been overturned.
• Horizontality– All rock layers were originally deposited horizontally.
• Lateral continuity– Originally deposited layers of rock extend laterally in all directions until either thinning out or being cut off by a different rock layer.
• Biologic succession (where applicable) – This states that each stratum in a succession contains a distinctive set of fossils. This allows for a correlation of the stratum even when the horizon between them is not continuous.
• Cross-cutting relationships– A rock feature that cuts across another feature must be younger than the rock it cuts across.
• Inclusion– Small fragments of one type of rock but embedded in a second type of rock must have formed first, and were included when the second rock was forming.
• Relationships ofunconformities– Geologic features representing periods of erosion or non-deposition, indicating non-continuous sediment deposition.

Terminology

See also:Stratigraphy,Chronostratigraphy,Biostratigraphy,Magnetostratigraphy,Lithostratigraphy,andGeochronology

The GTS is divided into chronostratigraphic units and their corresponding geochronologic units. These are represented on the ICC published by the ICS; however, regional terms are still in use in some areas.

Chronostratigraphyis the element ofstratigraphythat deals with the relation between rock bodies and the relative measurement of geological time.It is the process where distinct strata between defined stratigraphic horizons are assigned to represent a relative interval of geologic time.

Achronostratigraphic unitis a body of rock, layered or unlayered, that is defined between specified stratigraphic horizons which represent specified intervals of geologic time. They include all rocks representative of a specific interval of geologic time, and only this time span. Eonothem, erathem, system, series, subseries, stage, and substage are the hierarchical chronostratigraphic units. Geochronologyis the scientific branch of geology that aims to determine the age of rocks, fossils, and sediments either through absolute (e.g.,radiometric dating) or relative means (e.g.,stratigraphic position,paleomagnetism,stable isotope ratios).

Ageochronologic unitis a subdivision of geologic time. It is a numeric representation of an intangible property (time).Eon, era, period, epoch, subepoch, age, and subage are the hierarchical geochronologic units.Geochronometryis the field of geochronology that numerically quantifies geologic time.

AGlobal Boundary Stratotype Section and Point(GSSP) is an internationally agreed upon reference point on astratigraphic sectionwhich defines the lower boundaries of stages on the geologic time scale.(Recently this has been used to define the base of a system)

AGlobal Standard Stratigraphic Age(GSSA)is a numeric only, chronologic reference point used to define the base of geochronologic units prior to the Cryogenian. These points are arbitrarily defined.They are used where GSSPs have not yet been established. Research is ongoing to define GSSPs for the base of all units that are currently defined by GSSAs.

The numeric (geochronometric) representation of a geochronologic unit can, and is more often subject to change when geochronology refines the geochronometry, while the equivalent chronostratigraphic unit remains the same, and their revision is less common. For example, in early 2022 the boundary between theEdiacaranandCambrianperiods(geochronologic units) was revised from 541 Ma to 538.8 Ma but the rock definition of the boundary (GSSP) at the base of the Cambrian, and thus the boundary between the Ediacaran and Cambriansystems(chronostratigraphic units) has not changed, merely the geochronometry has been refined.

The numeric values on the ICC are represented by the unitMa(megaannum) 'millionyears', i.e., 201.4 ± 0.2 Ma, the lower boundary of theJurassicPeriod, is defined as 201,400,000 years old with an uncertainty of 200,000 years. OtherSI prefixunits commonly used by geologists areGa(gigaannum, billion years), andka(kiloannum, thousand years), with the latter often represented in calibrated units (before present).

Divisions of geologic time

• Aneonis the largest geochronologic time unit and is equivalent to a chronostratigraphiceonothem.There are four formally defined eons: theHadean,Archean,ProterozoicandPhanerozoic.
• Anerais the second largest geochronologic time unit and is equivalent to a chronostratigraphicerathem.There are ten defined eras: theEoarchean,Paleoarchean,Mesoarchean,Neoarchean,Paleoproterozoic,Mesoproterozoic,Neoproterozoic,Paleozoic,MesozoicandCenozoic,with none from the Hadean eon.
• Aperiodis equivalent to a chronostratigraphicsystem.There are 22 defined periods, with the current being theQuaternaryperiod.As an exception two subperiods are used for theCarboniferous Period.
• Anepochis the second smallest geochronologic unit. It is equivalent to a chronostratigraphicseries.There are 37 defined epochs and one informal one. There are also 11 subepochs which are all within theNeogeneand Quaternary.The use of subepochs as formal units in international chronostratigraphy was ratified in 2022.
• Anageis the smallest hierarchical geochronologic unit and is equivalent to a chronostratigraphicstage.There are 96 formal and five informal ages.
• Achronis a non-hierarchical formal geochronology unit of unspecified rank and is equivalent to a chronostratigraphicchronozone.These correlate withmagnetostratigraphic,lithostratigraphic,orbiostratigraphicunits as they are based on previously defined stratigraphic units or geologic features.

TheEarlyandLatesubdivisions are used as the geochronologic equivalents of the chronostratigraphicLowerandUpper,e.g., EarlyTriassicPeriod (geochronologic unit) is used in place of Lower Triassic Series (chronostratigraphic unit).

Rocks representing a given chronostratigraphic unit are that chronostratigraphic unit, and the time they were laid down in is the geochronologic unit, i.e., the rocks that represent theSilurianSeriesarethe Silurian Series and they were depositedduringthe Silurian Period.

Formal, hierarchical units of the geologic time scale (largest to smallest)

Chronostratigraphic unit (strata)	Geochronologic unit (time)	Time span
Eonothem	Eon	Several hundred million years to two billion years
Erathem	Era	Tens to hundreds of millions of years
System	Period	Millions of years to tens of millions of years
Series	Epoch	Hundreds of thousands of years to tens of millions of years
Subseries	Subepoch	Thousands of years to millions of years
Stage	Age	Thousands of years to millions of years

Naming of geologic time

The names of geologic time units are defined for chronostratigraphic units with the corresponding geochronologic unit sharing the same name with a change to the latter (e.g. PhanerozoicEonothembecomes the Phanerozoic Eon). Names of erathems in the Phanerozoic were chosen to reflect major changes in the history of life on Earth:Paleozoic(old life),Mesozoic(middle life), andCenozoic(new life). Names of systems are diverse in origin, with some indicating chronologic position (e.g., Paleogene), while others are named forlithology(e.g., Cretaceous),geography(e.g.,Permian), or are tribal (e.g.,Ordovician) in origin. Most currently recognised series and subseries are named for their position within a system/series (early/middle/late); however, the ICS advocates for all new series and subseries to be named for a geographic feature in the vicinity of itsstratotypeortype locality.The name of stages should also be derived from a geographic feature in the locality of its stratotype or type locality.

Informally, the time before the Cambrian is often referred to as thePrecambrianor pre-Cambrian (Supereon).

Time span andetymologyofICSeonothem/eon names

Name	Time span	Duration (million years)	Etymology of name
Phanerozoic	538.8 to 0million years ago	538.8	From Greek φανερός (phanerós) 'visible' or 'abundant' and ζωή (zoē) 'life'.
Proterozoic	2,500 to 538.8million years ago	1961.2	From Greek πρότερος (próteros) 'former' or 'earlier' and ζωή (zoē) 'life'.
Archean	4,031 to 2,500million years ago	1531	From Greekἀρχή(archē) 'beginning, origin'.
Hadean	4,567.3 to 4,031million years ago	536.3	FromHades,Greek:ᾍδης,translit.Háidēs,the god of the underworld (hell, the inferno) in Greek mythology.

Time span and etymology of ICS erathem/era names

Name	Time span	Duration (million years)	Etymology of name
Cenozoic	66 to 0million years ago	66	From Greek καινός (kainós) 'new' and ζωή (zōḗ) 'life'.
Mesozoic	251.9 to 66million years ago	185.902	From Greek μέσο (méso) 'middle' and ζωή (zōḗ) 'life'.
Paleozoic	538.8 to 251.9million years ago	286.898	From Greek παλιός (palaiós) 'old' and ζωή (zōḗ) 'life'.
Neoproterozoic	1,000 to 538.8million years ago	461.2	From Greek νέος (néos) 'new' or 'young', πρότερος (próteros) 'former' or 'earlier', and ζωή (zōḗ) 'life'.
Mesoproterozoic	1,600 to 1,000million years ago	600	From Greek μέσο (méso) 'middle', πρότερος (próteros) 'former' or 'earlier', and ζωή (zōḗ) 'life'.
Paleoproterozoic	2,500 to 1,600million years ago	900	From Greek παλιός (palaiós) 'old', πρότερος (próteros) 'former' or 'earlier', and ζωή (zōḗ) 'life'.
Neoarchean	2,800 to 2,500million years ago	300	From Greek νέος (néos) 'new' or 'young' and ἀρχαῖος (arkhaîos) 'ancient'.
Mesoarchean	3,200 to 2,800million years ago	400	From Greek μέσο (méso) 'middle' and ἀρχαῖος (arkhaîos) 'ancient'.
Paleoarchean	3,600 to 3,200million years ago	400	From Greek παλιός (palaiós) 'old' and ἀρχαῖος (arkhaîos) 'ancient'.
Eoarchean	4,031 to 3,600million years ago	431	From Greek ἠώς (ēōs) 'dawn' and ἀρχαῖος (arkhaîos) 'ancient'.

Time span and etymology of ICS system/period names

Name	Time span	Duration (million years)	Etymology of name
Quaternary	2.6 to 0million years ago	2.58	First introduced byJules Desnoyersin 1829 for sediments inFrance'sSeineBasin that appeared to be younger thanTertiaryrocks.
Neogene	23 to 2.6million years ago	20.45	Derived from Greek νέος (néos) 'new' and γενεά (geneá) 'genesis' or 'birth'.
Paleogene	66 to 23million years ago	42.97	Derived from Greek παλιός (palaiós) 'old' and γενεά (geneá) 'genesis' or 'birth'.
Cretaceous	~145 to 66million years ago	~79	Derived fromTerrain Crétacéused in 1822 byJean d'Omalius d'Halloyin reference to extensive beds ofchalkwithin theParis Basin.Ultimately derived fromLatincrēta'chalk'.
Jurassic	201.4 to 145million years ago	~56.4	Named after theJura Mountains.Originally used byAlexander von Humboldtas 'Jura Kalkstein' (Jura limestone) in 1799.Alexandre Brongniartwas the first to publish the term Jurassic in 1829.
Triassic	251.9 to 201.4million years ago	50.502	From theTriasofFriedrich August von Albertiin reference to a trio of formations widespread in southernGermany
Permian	298.9 to 251.9million years ago	46.998	Named after the historical region ofPerm,Russian Empire.
Carboniferous	358.9 to 298.9million years ago	60	Means 'coal-bearing', from theLatincarbō (coal) and ferō (to bear, carry).
Devonian	419.2 to 358.9million years ago	60.3	Named afterDevon,England.
Silurian	443.8 to 419.2million years ago	24.6	Named after theCeltictribe, theSilures.
Ordovician	485.4 to 443.8million years ago	41.6	Named after the Celtic tribe,Ordovices.
Cambrian	538.8 to 485.4million years ago	53.4	Named forCambria,alatinisedform of the Welsh name forWales,Cymru.
Ediacaran	635 to 538.8million years ago	~96.2	Named for theEdiacara Hills.Ediacara is possibly a corruption ofKuyani'Yata Takarra' 'hard or stony ground'.
Cryogenian	720 to 635million years ago	~85	From Greek κρύος (krýos) 'cold' and γένεσις (génesis) 'birth'.
Tonian	1,000 to 720million years ago	~280	From Greek τόνος (tónos) 'stretch'.
Stenian	1,200 to 1,000million years ago	200	From Greek στενός (stenós) 'narrow'.
Ectasian	1,400 to 1,200million years ago	200	From Greek ἔκτᾰσῐς (éktasis) 'extension'.
Calymmian	1,600 to 1,400million years ago	200	From Greek κάλυμμᾰ (kálumma) 'cover'.
Statherian	1,800 to 1,600million years ago	200	From Greek σταθερός (statherós) 'stable'.
Orosirian	2,050 to 1,800million years ago	250	From Greek ὀροσειρά (oroseirá) 'mountain range'.
Rhyacian	2,300 to 2,050million years ago	250	From Greek ῥύαξ (rhýax) 'stream of lava'.
Siderian	2,500 to 2,300million years ago	200	From Greek σίδηρος (sídēros) 'iron'.

Time span and etymology of ICS series/epoch names

Name	Time span	Duration (million years)	Etymology of name
Holocene	0.012 to 0million years ago	0.0117	From Greek ὅλος (hólos) 'whole' and καινός (kainós) 'new'
Pleistocene	2.58 to 0.012million years ago	2.5683	Coined in the early 1830s from Greek πλεῖστος (pleîstos) 'most' and καινός (kainós) 'new'
Pliocene	5.33 to 2.58million years ago	2.753	Coined in the early 1830s from Greek πλείων (pleíōn) 'more' and καινός (kainós) 'new'
Miocene	23.03 to 5.33million years ago	17.697	Coined in the early 1830s from Greek μείων (meíōn) 'less' and καινός (kainós) 'new'
Oligocene	33.9 to 23.03million years ago	10.87	Coined in the 1850s from Greek ὀλίγος (olígos) 'few' and καινός (kainós) 'new'
Eocene	56 to 33.9million years ago	22.1	Coined in the early 1830s from Greek ἠώς (ēōs) 'dawn' and καινός (kainós) 'new', referring to the dawn of modern life during this epoch
Paleocene	66 to 56million years ago	10	Coined byWilhelm Philippe Schimperin 1874 as a portmanteau of paleo- + Eocene, but on the surface from Greek παλαιός (palaios) 'old' and καινός (kainós) 'new'
Upper Cretaceous	100.5 to 66million years ago	34.5	SeeCretaceous
Lower Cretaceous	145 to 100.5million years ago	44.5
Upper Jurassic	161.5 to 145million years ago	16.5	SeeJurassic
Middle Jurassic	174.7 to 161.5million years ago	13.2
Lower Jurassic	201.4 to 174.7million years ago	26.7
Upper Triassic	237 to 201.4million years ago	35.6	SeeTriassic
Middle Triassic	247.2 to 237million years ago	10.2
Lower Triassic	251.9 to 247.2million years ago	4.702
Lopingian	259.51 to 251.9million years ago	7.608	Named forLoping,China, an anglicization of Mandarin nhạc bình (lèpíng) 'peaceful music'
Guadalupian	273.01 to 259.51million years ago	13.5	Named for theGuadalupe Mountainsof the American Southwest, ultimately from Arabic وَادِي ٱل (wādī al) 'valley of the' and Latinlupus'wolf' via Spanish
Cisuralian	298.9 to 273.01million years ago	25.89	From Latincis-(before) + Russian Урал (Ural), referring to the western slopes of theUral Mountains
Upper Pennsylvanian	307 to 298.9million years ago	8.1	Named for the US state ofPennsylvania,fromWilliam Penn+ Latinsilvanus(forest) + -ia by analogy to Transylvania
Middle Pennsylvanian	315.2 to 307million years ago	8.2
Lower Pennsylvanian	323.2 to 315.2million years ago	8
Upper Mississippian	330.9 to 323.2million years ago	7.7	Named for theMississippi River,from Ojibwe ᒥᐦᓯᓰᐱ (misi-ziibi) 'great river'
Middle Mississippian	346.7 to 330.9million years ago	15.8
Lower Mississippian	358.9 to 346.7million years ago	12.2
Upper Devonian	382.7 to 358.9million years ago	23.8	SeeDevonian
Middle Devonian	393.3 to 382.7million years ago	10.6
Lower Devonian	419.2 to 393.3million years ago	25.9
Pridoli	423 to 419.2million years ago	3.8	Named for the Homolka a Přídolí nature reserve nearPrague,Czechia
Ludlow	427.4 to 423million years ago	4.4	Named afterLudlow,England
Wenlock	433.4 to 427.4million years ago	6	Named for theWenlock EdgeinShropshire,England
Llandovery	443.8 to 433.4million years ago	10.4	Named afterLlandovery,Wales
Upper Ordovician	458.4 to 443.8million years ago	14.6	SeeOrdovician
Middle Ordovician	470 to 458.4million years ago	11.6
Lower Ordovician	485.4 to 470million years ago	15.4
Furongian	497 to 485.4million years ago	11.6	From Mandarin phù dung (fúróng) 'lotus', referring to the state symbol ofHunan
Miaolingian	509 to 497million years ago	12	Named for theMiao Lingmountains ofGuizhou,Mandarin for 'sprouting peaks'
Cambrian Series 2(informal)	521 to 509million years ago	12	SeeCambrian
Terreneuvian	538.8 to 521million years ago	17.8	Named forTerre-Neuve,a FrenchcalqueofNewfoundland

History of the geologic time scale

See also:History of geologyandHistory of paleontology

Early history

While a modern geological time scale was not formulated until 1911byArthur Holmes,the broader concept that rocks and time are related can be traced back to (at least) thephilosophersofAncient Greece.Xenophanes of Colophon(c. 570–487BCE) observed rock beds with fossils of shells located above the sea-level, viewed them as once living organisms, and used this to imply an unstable relationship in which the sea had at timestransgressedover the land and at other times hadregressed.This view was shared by a few of Xenophanes' contemporaries and those that followed, includingAristotle(384–322 BCE) who (with additional observations) reasoned that the positions of land and sea had changed over long periods of time. The concept ofdeep timewas also recognised byChinese naturalistShen Kuo(1031–1095) andIslamicscientist-philosophers, notably theBrothers of Purity,who wrote on the processes of stratification over the passage of time in theirtreatises.Their work likely inspired that of the 11th-centuryPersianpolymathAvicenna(Ibn Sînâ, 980–1037) who wrote inThe Book of Healing(1027) on the concept of stratification and superposition, pre-datingNicolas Stenoby more than six centuries.Avicenna also recognised fossils as "petrifications of the bodies of plants and animals",with the 13th-centuryDominicanbishopAlbertus Magnus(c. 1200–1280) extending this into a theory of a petrifying fluid.These works appeared to have little influence onscholarsinMedieval Europewho looked to theBibleto explain the origins of fossils and sea-level changes, often attributing these to the 'Deluge', includingRistoro d'Arezzoin 1282.It was not until theItalian RenaissancewhenLeonardo da Vinci(1452–1519) would reinvigorate the relationships between stratification, relative sea-level change, and time, denouncing attribution of fossils to the 'Deluge':

Of the stupidity and ignorance of those who imagine that these creatures were carried to such places distant from the sea by the Deluge...Why do we find so many fragments and whole shells between the different layers of stone unless they had been upon the shore and had been covered over by earth newly thrown up by the sea which then became petrified? And if the above-mentioned Deluge had carried them to these places from the sea, you would find the shells at the edge of one layer of rock only, not at the edge of many where may be counted the winters of the years during which the sea multiplied the layers of sand and mud brought down by the neighboring rivers and spread them over its shores. And if you wish to say that there must have been many deluges in order to produce these layers and the shells among them it would then become necessary for you to affirm that such a deluge took place every year.

These views of da Vinci remained unpublished, and thus lacked influence at the time; however, questions of fossils and their significance were pursued and, while views againstGenesiswere not readily accepted and dissent fromreligiousdoctrine was in some places unwise, scholars such asGirolamo Fracastoroshared da Vinci's views, and found the attribution of fossils to the 'Deluge' absurd.

Establishment of primary principles

Niels Stensen, more commonly known as Nicolas Steno (1638–1686), is credited with establishing four of the guiding principles of stratigraphy.InDe solido intra solidum naturaliter contento dissertationis prodromusSteno states:

• When any given stratum was being formed, all the matter resting on it was fluid and, therefore, when the lowest stratum was being formed, none of the upper strata existed.
• ...strata which are either perpendicular to the horizon or inclined to it were at one time parallel to the horizon.
• When any given stratum was being formed, it was either encompassed at its edges by another solid substance or it covered the whole globe of the earth. Hence, it follows that wherever bared edges of strata are seen, either a continuation of the same strata must be looked for or another solid substance must be found that kept the material of the strata from being dispersed.
• If a body or discontinuity cuts across a stratum, it must have formed after that stratum.

Respectively, these are the principles of superposition, original horizontality, lateral continuity, and cross-cutting relationships. From this Steno reasoned that strata were laid down in succession and inferred relative time (in Steno's belief, time fromCreation). While Steno's principles were simple and attracted much attention, applying them proved challenging.These basic principles, albeit with improved and more nuanced interpretations, still form the foundational principles of determining the correlation of strata relative to geologic time.

Over the course of the 18th-century geologists realised that:

• Sequences of strata often become eroded, distorted, tilted, or even inverted after deposition
• Strata laid down at the same time in different areas could have entirely different appearances
• The strata of any given area represented only part of Earth's long history

Formulation of a modern geologic time scale

The apparent, earliest formal division of the geologic record with respect to time was introduced byThomas Burnetwho applied a two-fold terminology to mountains by identifying "montes primarii"for rock formed at the time of the 'Deluge', and younger"monticulos secundarios "formed later from the debris of the "primarii ".This attribution to the 'Deluge', while questioned earlier by the likes of da Vinci, was the foundation ofAbraham Gottlob Werner's (1749–1817)Neptunismtheory in which all rocks precipitated out of a single flood.A competing theory,Plutonism,was developed byAnton Moro(1687–1784) and also used primary and secondary divisions for rock units.In this early version of the Plutonism theory, the interior of Earth was seen as hot, and this drove the creation of primary igneous and metamorphic rocks and secondary rocks formed contorted and fossiliferous sediments. These primary and secondary divisions were expanded on byGiovanni Targioni Tozzetti(1712–1783) andGiovanni Arduino(1713–1795) to include tertiary and quaternary divisions.These divisions were used to describe both the time during which the rocks were laid down, and the collection of rocks themselves (i.e., it was correct to say Tertiary rocks, and Tertiary Period). Only the Quaternary division is retained in the modern geologic time scale, while the Tertiary division was in use until the early 21st century. The Neptunism and Plutonism theories would compete into the early19th centurywith a key driver for resolution of this debate being the work ofJames Hutton(1726–1797), in particular hisTheory of the Earth,first presented before theRoyal Society of Edinburghin 1785.Hutton's theory would later become known asuniformitarianism,popularised byJohn Playfair(1748–1819) and laterCharles Lyell(1797–1875) in hisPrinciples of Geology.Their theories strongly contested the 6,000 year age of the Earth as suggested determined byJames Usshervia Biblical chronology that was accepted at the time by western religion. Instead, using geological evidence, they contested Earth to be much older, cementing the concept of deep time.

During the early 19th centuryWilliam Smith,Georges Cuvier,Jean d'Omalius d'Halloy,andAlexandre Brongniartpioneered the systematic division of rocks by stratigraphy and fossil assemblages. These geologists began to use the local names given to rock units in a wider sense, correlating strata across national and continental boundaries based on their similarity to each other. Many of the names below erathem/era rank in use on the modern ICC/GTS were determined during the early to mid-19th century.

The advent of geochronometry

During the 19th century, the debate regarding Earth's age was renewed, with geologists estimating ages based ondenudationrates and sedimentary thicknesses or ocean chemistry, and physicists determining ages for the cooling of the Earth or the Sun using basicthermodynamicsor orbital physics.These estimations varied from 15,000 million years to 0.075 million years depending on method and author, but the estimations ofLord KelvinandClarence Kingwere held in high regard at the time due to their pre-eminence in physics and geology. All of these early geochronometric determinations would later prove to be incorrect.

The discovery ofradioactive decaybyHenri Becquerel,Marie Curie,andPierre Curielaid the ground work for radiometric dating, but the knowledge and tools required for accurate determination of radiometric ages would not be in place until the mid-1950s.Early attempts at determining ages of uranium minerals and rocks byErnest Rutherford,Bertram Boltwood,Robert Strutt,and Arthur Holmes, would culminate in what are considered the first international geological time scales by Holmes in 1911 and 1913.The discovery ofisotopesin 1913byFrederick Soddy,and the developments inmass spectrometrypioneered byFrancis William Aston,Arthur Jeffrey Dempster,andAlfred O. C. Nierduring the early to mid-20th centurywould finally allow for the accurate determination of radiometric ages, with Holmes publishing several revisions to hisgeological time-scalewith his final version in 1960.

Modern international geologic time scale

The establishment of the IUGS in 1961and acceptance of the Commission on Stratigraphy (applied in 1965)to become a member commission of IUGS led to the founding of the ICS. One of the primary objectives of the ICS is "the establishment, publication and revision of the ICS International Chronostratigraphic Chart which is the standard, reference global Geological Time Scale to include the ratified Commission decisions".

Following on from Holmes, severalA Geological Time Scalebooks were published in 1982,1989,2004,2008,2012,2016,and 2020.However, since 2013, the ICS has taken responsibility for producing and distributing the ICC citing the commercial nature, independent creation, and lack of oversight by the ICS on the prior published GTS versions (GTS books prior to 2013) although these versions were published in close association with the ICS.SubsequentGeologic Time Scalebooks (2016and 2020) are commercial publications with no oversight from the ICS, and do not entirely conform to the chart produced by the ICS. The ICS produced GTS charts are versioned (year/month) beginning at v2013/01. At least one new version is published each year incorporating any changes ratified by the ICS since the prior version.

The following five timelines show the geologic time scale to scale. The first shows the entire time from the formation of the Earth to the present, but this gives little space for the most recent eon. The second timeline shows an expanded view of the most recent eon. In a similar way, the most recent era is expanded in the third timeline, the most recent period is expanded in the fourth timeline, and the most recent epoch is expanded in the fifth timeline.

Horizontal scale is Millions of years (above timelines) / Thousands of years (below timeline)

Major proposed revisions to the ICC

Proposed Anthropocene Series/Epoch

Main article:Anthropocene

First suggested in 2000,theAnthropoceneis a proposed epoch/series for the most recent time in Earth's history. While still informal, it is a widely used term to denote the present geologic time interval, in which many conditions and processes on Earth are profoundly altered by human impact.As of April 2022the Anthropocene has not been ratified by the ICS; however, in May 2019 theAnthropocene Working Groupvoted in favour of submitting a formal proposal to the ICS for the establishment of the Anthropocene Series/Epoch.Nevertheless, the definition of the Anthropocene as a geologic time period rather than a geologic event remains controversial and difficult.

Proposals for revisions to pre-Cryogenian timeline

Shields et al. 2021

An international working group of the ICS on pre-Cryogenian chronostratigraphic subdivision have outlined a template to improve the pre-Cryogenian geologic time scale based on the rock record to bring it in line with the post-Tonian geologic time scale.This work assessed the geologic history of the currently defined eons and eras of the pre-Cambrian,and the proposals in the "Geological Time Scale" books2004,2012,and2020.Their recommend revisionsof the pre-Cryogenian geologic time scale were (changes from the current scale [v2023/09] are italicised):

• Three divisions of the Archean instead of four by dropping Eoarchean, and revisions to their geochronometric definition, along with the repositioning of the Siderian into the latest Neoarchean, and a potential Kratian division in the Neoarchean.
  • Archean (4000–2450Ma)
    • Paleoarchean (4000–3500Ma)
    • Mesoarchean (3500–3000Ma)
    • Neoarchean (3000–2450Ma)
      • Kratian(no fixed time given, prior to the Siderian) – from Greek κράτος (krátos) 'strength'.
      • Siderian (?–2450Ma) – moved from Proterozoic to end of Archean, no start time given, base of Paleoproterozoic defines the end of the Siderian
• Refinement of geochronometric divisions of the Proterozoic, Paleoproterozoic, repositioning of the Statherian into the Mesoproterozoic, new Skourian period/system in the Paleoproterozoic, new Kleisian or Syndian period/system in the Neoproterozoic.
  • Paleoproterozoic (2450–1800Ma)
    • Skourian(2450–2300 Ma) – from Greek σκουριά (skouriá) 'rust'.
    • Rhyacian (2300–2050 Ma)
    • Orosirian (2050–1800 Ma)
  • Mesoproterozoic (1800–1000 Ma)
    • Statherian(1800–1600 Ma)
    • Calymmian (1600–1400 Ma)
    • Ectasian (1400-1200 Ma)
    • Stenian (1200–1000 Ma)
  • Neoproterozoic (1000–538.8 Ma)
    • KleisianorSyndian(1000–800Ma) – respectively from Greek κλείσιμο (kleísimo) 'closure' and σύνδεση (sýndesi) 'connection'.
    • Tonian (800–720 Ma)
    • Cryogenian (720–635 Ma)
    • Ediacaran (635–538.8 Ma)

Proposed pre-Cambrian timeline (Shield et al. 2021, ICS working group on pre-Cryogenian chronostratigraphy), shown to scale:

Current ICC pre-Cambrian timeline (v2023/09), shown to scale:

Van Kranendonk et al. 2012 (GTS2012)

The book,Geologic Time Scale 2012,was the last commercial publication of an international chronostratigraphic chart that was closely associated with the ICS.It included a proposal to substantially revise the pre-Cryogenian time scale to reflect important events such as theformation of the Solar Systemand theGreat Oxidation Event,among others, while at the same time maintaining most of the previous chronostratigraphic nomenclature for the pertinent time span.As of April 2022these proposed changes have not been accepted by the ICS. The proposed changes (changes from the current scale [v2023/09]) are italicised:

• Hadean Eon (4567–4030Ma)
  • ChaotianEra/Erathem (4567–4404 Ma) – the name alluding both to themythological Chaosand thechaoticphase ofplanet formation.
  • Jack HillsianorZirconianEra/Erathem (4404–4030Ma) – both names allude to the Jack Hills Greenstone Belt which provided the oldest mineral grains on Earth,zircons.
• Archean Eon/Eonothem (4030–2420Ma)
  • Paleoarchean Era/Erathem (4030–3490Ma)
    • AcastanPeriod/System (4030–3810Ma) – named after theAcasta Gneiss,one of the oldest preserved pieces ofcontinental crust.
    • IsuanPeriod (3810–3490Ma) – named after theIsua Greenstone Belt.
  • Mesoarchean Era/Erathem (3490–2780Ma)
    • VaalbaranPeriod/System (3490–3020Ma) – based on the names of theKapvaal(Southern Africa) andPilbara(Western Australia)cratons,to reflect the growth of stable continental nuclei or proto-cratonickernels.
    • PongolanPeriod/System (3020–2780Ma) – named after the Pongola Supergroup, in reference to the well preserved evidence of terrestrial microbial communities in those rocks.
  • Neoarchean Era/Erathem (2780–2420Ma)
    • MethanianPeriod/System (2780–2630Ma) – named for the inferred predominance ofmethanotrophicprokaryotes
    • Siderian Period/System (2630–2420Ma) – named for the voluminousbanded iron formationsformed within its duration.
• Proterozoic Eon/Eonothem (2420–538.8 Ma)
  • Paleoproterozoic Era/Erathem (2420–1780Ma)
    • OxygenianPeriod/System (2420–2250Ma) – named for displaying the first evidence for a global oxidising atmosphere.
    • JatulianorEukaryianPeriod/System (2250–2060Ma) – names are respectively for the Lomagundi–Jatuli δ¹³C isotopic excursion event spanning its duration, and for the (proposed)first fossil appearance ofeukaryotes.
    • Columbian Period/System(2060–1780Ma) – named after thesupercontinentColumbia.
  • Mesoproterozoic Era/Erathem (1780–850Ma)
    • RodinianPeriod/System (1780–850Ma) – named after the supercontinentRodinia,stable environment.

Proposed pre-Cambrian timeline (GTS2012), shown to scale:

Current ICC pre-Cambrian timeline (v2023/09), shown to scale:

Table of geologic time

The following table summarises the major events and characteristics of the divisions making up the geologic time scale of Earth. This table is arranged with the most recent geologic periods at the top, and the oldest at the bottom. The height of each table entry does not correspond to the duration of each subdivision of time. As such, this table is not to scale and does not accurately represent the relative time-spans of each geochronologic unit. While thePhanerozoicEon looks longer than the rest, it merely spans ~539 million years (~12% of Earth's history), whilst the previous three eonscollectively span ~3,461 million years (~76% of Earth's history). This bias toward the most recent eon is in part due to the relative lack of information about events that occurred during the first three eons compared to the current eon (the Phanerozoic).The use of subseries/subepochs has been ratified by the ICS.

The content of the table is based on the official ICC produced and maintained by the ICS who also provide an online interactive version of this chart. The interactive version is based on a service delivering a machine-readableResource Description Framework/Web Ontology Languagerepresentation of the time scale, which is available through theCommission for the Management and Application of Geoscience InformationGeoSciMLproject as a serviceand at aSPARQLend-point.

Eonothem/ Eon	Erathem/ Era	System/ Period	Series/ Epoch	Stage/ Age	Major events	Start, million years ago
Phanerozoic	Cenozoic	Quaternary	Holocene	Meghalayan	4.2-kiloyear event,Austronesian expansion,increasingindustrialCO2.	0.0042*
				Northgrippian	8.2-kiloyear event,Holocene climatic optimum.Sea levelflooding ofDoggerlandandSundaland.Saharabecomes a desert. End of Stone Age and start ofrecorded history.Humans finally expand into theArctic ArchipelagoandGreenland.	0.0082*
				Greenlandian	Climate stabilises. CurrentinterglacialandHolocene extinctionbegins.Agriculture begins.Humans spread across thewet SaharaandArabia,theExtreme North,and the Americas (mainland and theCaribbean).	0.0117 ± 0.000099*
			Pleistocene	Upper/Late('Tarantian')	Eemianinterglacial,last glacial period,ending withYounger Dryas.Toba eruption.Pleistocene megafauna (including the last terror birds) extinction.Humans expand intoNear Oceaniaand theAmericas.	0.129
				Chibanian	Mid-Pleistocene Transitionoccurs, high amplitude100 kaglacial cycles.Rise ofHomo sapiens.	0.774*
				Calabrian	Further cooling of the climate. Giantterror birdsgo extinct. Spread ofHomo erectusacrossAfro-Eurasia.	1.8*
				Gelasian	Start ofQuaternary glaciationsand unstable climate.Rise of thePleistocene megafaunaandHomo habilis.	2.58*
		Neogene	Pliocene	Piacenzian	Greenland ice sheetdevelopsas the cold slowly intensifies towards the Pleistocene. AtmosphericO2and CO2content reaches present-day levels while landmasses also reach their current locations (e.g. theIsthmus of Panamajoins theNorthandSouth Americas,while allowinga faunal interchange). The last non-marsupial metatherians go extinct.Australopithecuscommon in East Africa;Stone Agebegins.	3.6*
				Zanclean	Zanclean floodingof theMediterranean Basin.Cooling climate continues from the Miocene. Firstequinesandelephantines.Ardipithecusin Africa.	5.333*
			Miocene	Messinian	Messinian Eventwith hypersaline lakes in emptyMediterranean Basin.Sahara desert formation begins.Moderate icehouse climate,punctuated byice agesand re-establishment ofEast Antarctic Ice Sheet.Choristoderes,the last non-crocodiliancrocodylomorphsandcreodontsgo extinct. Afterseparating from gorilla ancestors,chimpanzee and human ancestorsgradually separate;SahelanthropusandOrrorinin Africa.	7.246*
				Tortonian		11.63*
				Serravallian	Middle Miocene climate optimum temporarily provides a warm climate.Extinctions inmiddle Miocene disruption,decreasing shark diversity. Firsthippos.Ancestor ofgreat apes.	13.82*
				Langhian		15.98*
				Burdigalian	OrogenyinNorthern Hemisphere.Start ofKaikoura OrogenyformingSouthern Alps in New Zealand.Widespread forests slowlydraw inmassive amounts of CO2,gradually lowering the level of atmospheric CO2from 650ppmvdown to around 100 ppmv during the Miocene.Modernbirdand mammal families become recognizable. The last of the primitive whales go extinct.Grassesbecome ubiquitous. Ancestor ofapes,including humans.Afro-Arabia collides with Eurasia, fully forming theAlpide Beltand closing the Tethys Ocean, while allowing a faunal interchange. At the same time, Afro-Arabia splits intoAfricaandWest Asia.	20.44
				Aquitanian		23.03*
		Paleogene	Oligocene	Chattian	Grande Coupureextinction. Start of widespreadAntarctic glaciation.Rapidevolutionand diversification of fauna, especiallymammals(e.g. firstmacropodsandseals). Major evolution and dispersal of modern types offlowering plants.Cimolestans,miacoids and condylarths go extinct. Firstneocetes(modern, fully aquatic whales) appear.	27.82*
				Rupelian		33.9*
			Eocene	Priabonian	Moderate, cooling climate.Archaicmammals(e.g.creodonts,miacoids,"condylarths"etc.) flourish and continue to develop during the epoch. Appearance of several" modern "mammal families.Primitive whalesandsea cowsdiversify after returning to water.Birdscontinue to diversify. Firstkelp,diprotodonts,bearsandsimians.The multituberculates and leptictidans go extinct by the end of the epoch. Reglaciation of Antarctica and formation of itsice cap;End ofLaramideandSevier Orogeniesof theRocky Mountainsin North America.Hellenic Orogenybegins in Greece andAegean Sea.	37.71*
				Bartonian		41.2
				Lutetian		47.8*
				Ypresian	Two transient events of global warming (PETMandETM-2) and warming climate until theEocene Climatic Optimum.TheAzolla eventdecreased CO2levels from 3500ppmto 650 ppm, setting the stage for a long period of cooling.Greater Indiacollides with Eurasia and startsHimalayan Orogeny(allowing abiotic interchange) while Eurasia completely separates from North America, creating theNorth Atlantic Ocean.Maritime Southeast Asiadiverges from the rest of Eurasia. Firstpasserines,ruminants,pangolins,batsand trueprimates.	56*
			Paleocene	Thanetian	Starts withChicxulub impactand theK–Pg extinction event,wiping out all non-avian dinosaurs and pterosaurs, most marine reptiles, many other vertebrates (e.g. many Laurasian metatherians), most cephalopods (onlyNautilidaeandColeoideasurvived) and many other invertebrates.Climate tropical.Mammalsandbirds(avians) diversify rapidly into a number of lineages following the extinction event (while the marine revolution stops). Multituberculates and the firstrodentswidespread. First large birds (e.g.ratitesandterror birds) and mammals (up to bear or small hippo size).Alpine orogenyin Europe and Asia begins. Firstproboscideansandplesiadapiformes(stem primates) appear.Some marsupialsmigrate to Australia.	59.2*
				Selandian		61.6*
				Danian		66*
	Mesozoic	Cretaceous	Upper/Late	Maastrichtian	Flowering plantsproliferate (after developing many features since the Carboniferous), along with new types ofinsects,while other seed plants (gymnosperms and seed ferns) decline. More modernteleostfish begin to appear.Ammonoids,belemnites,rudistbivalves,sea urchinsandspongesall common. Many new types ofdinosaurs(e.g.tyrannosaurs,titanosaurs,hadrosaurs,andceratopsids) evolve on land, whilecrocodiliansappear in water and probably cause the last temnospondyls to die out; andmosasaursand modern types of sharks appear in the sea. The revolution started by marine reptiles and sharks reaches its peak, though ichthyosaurs vanish a few million years after being heavily reduced at theBonarelli Event.Toothed andtoothless avian birdscoexist with pterosaurs. Modernmonotremes,metatherian(includingmarsupials,who migrate to South America) andeutherian(includingplacentals,leptictidansandcimolestans) mammals appear while the last non-mammalian cynodonts die out. Firstterrestrial crabs.Many snails become terrestrial. Further breakup of Gondwana createsSouth America,Afro-Arabia,Antarctica,Oceania,Madagascar,Greater India,and theSouth Atlantic,IndianandAntarctic Oceansand the islands of the Indian (and some of the Atlantic) Ocean. Beginning ofLaramideandSevier Orogeniesof theRocky Mountains.Atmosphericoxygen and carbon dioxide levels similar to present day.Acritarchsdisappear. Climate initially warm, but later it cools.	72.1 ± 0.2*
				Campanian		83.6 ± 0.2*
				Santonian		86.3 ± 0.5*
				Coniacian		89.8 ± 0.3*
				Turonian		93.9*
				Cenomanian		100.5*
			Lower/Early	Albian		~113*
				Aptian		~121.4
				Barremian		~125.77*
				Hauterivian		~132.6*
				Valanginian		~139.8
				Berriasian		~145
		Jurassic	Upper/Late	Tithonian	Climate becomes humid again.Gymnosperms(especiallyconifers,cycadsandcycadeoids) andfernscommon.Dinosaurs,includingsauropods,carnosaurs,stegosaursandcoelurosaurs,become the dominant land vertebrates. Mammals diversify intoshuotheriids,australosphenidans,eutriconodonts,multituberculates,symmetrodonts,dryolestidsandboreosphenidansbut mostly remain small. Firstbirds,lizards, snakesandturtles.Firstbrown algae,rays,shrimps,crabsandlobsters.Parvipelvianichthyosaurs andplesiosaursdiverse. Rhynchocephalians throughout the world.Bivalves,ammonoidsandbelemnitesabundant.Sea urchinsvery common, along withcrinoids,starfish,sponges,andterebratulidandrhynchonellidbrachiopods.Breakup ofPangaeaintoLaurasiaandGondwana,with the latter also breaking into two main parts; thePacificandArctic Oceansform.Tethys Oceanforms.Nevadan orogenyin North America.RangitataandCimmerian orogeniestaper off. Atmospheric CO2levels 3–4 times the present-day levels (1200–1500 ppmv, compared to today's 400 ppmv).Crocodylomorphs(last pseudosuchians) seek out an aquatic lifestyle.Mesozoic marine revolutioncontinues from late Triassic.Tentaculitansdisappear.	149.2 ± 0.9
				Kimmeridgian		154.8 ± 1.0*
				Oxfordian		161.5 ± 1.0
			Middle	Callovian		165.3 ± 1.2
				Bathonian		168.2 ± 1.3*
				Bajocian		170.9 ± 1.4*
				Aalenian		174.7 ± 1.0*
			Lower/Early	Toarcian		184.2 ± 0.7*
				Pliensbachian		192.9 ± 1.0*
				Sinemurian		199.5 ± 0.3*
				Hettangian		201.4 ± 0.2*
		Triassic	Upper/Late	Rhaetian	Archosaursdominant on land aspseudosuchiansand in the air aspterosaurs.Dinosaursalso arise from bipedal archosaurs.Ichthyosaursandnothosaurs(a group of sauropterygians) dominate large marine fauna.Cynodontsbecome smaller and nocturnal, eventually becoming the first truemammals,while other remaining synapsids die out.Rhynchosaurs(archosaur relatives) also common.Seed fernscalledDicroidiumremained common in Gondwana, before being replaced by advanced gymnosperms. Many large aquatictemnospondylamphibians.Ceratitidanammonoidsextremely common.Modern coralsandteleostfish appear, as do many moderninsectorders and suborders. Firststarfish.Andean Orogenyin South America.Cimmerian Orogenyin Asia.Rangitata Orogenybegins in New Zealand.Hunter-Bowen OrogenyinNorthern Australia,Queensland andNew South Walesends, (c. 260–225 Ma).Carnian pluvial eventoccurs around 234–232 Ma, allowing the first dinosaurs andlepidosaurs(includingrhynchocephalians) to radiate.Triassic–Jurassic extinction eventoccurs 201 Ma, wiping out allconodontsand thelast parareptiles,many marine reptiles (e.g. all sauropterygians exceptplesiosaursand all ichthyosaurs exceptparvipelvians), allcrocopodansexcept crocodylomorphs, pterosaurs, and dinosaurs, and many ammonoids (including the wholeCeratitida), bivalves, brachiopods, corals and sponges. Firstdiatoms.	~208.5
				Norian		~227
				Carnian		~237*
			Middle	Ladinian		~242*
				Anisian		247.2
			Lower/Early	Olenekian		251.2
				Induan		251.902 ± 0.024*
	Paleozoic	Permian	Lopingian	Changhsingian	Landmassesunite intosupercontinentPangaea,creating theUrals,OuachitasandAppalachians,among other mountain ranges (the superoceanPanthalassaor Proto-Pacific also forms). End of Permo-Carboniferous glaciation. Hot and dry climate. A possible drop in oxygen levels.Synapsids(pelycosaursandtherapsids) become widespread and dominant, whileparareptilesandtemnospondylamphibiansremain common, with the latter probably giving rise tomodern amphibiansin this period. In the mid-Permian, lycophytes are heavily replaced by ferns and seed plants.Beetlesandfliesevolve. The very large arthropods and non-tetrapod tetrapodomorphs go extinct. Marine life flourishes in warm shallow reefs;productidandspiriferidbrachiopods, bivalves,forams,ammonoids (including goniatites), andorthoceridansall abundant.Crown reptilesarise from earlier diapsids, and split into the ancestors oflepidosaurs,kuehneosaurids,choristoderes,archosaurs,testudinatans,ichthyosaurs,thalattosaurs,andsauropterygians.Cynodonts evolve from larger therapsids.Olson's Extinction(273 Ma),End-Capitanian extinction(260 Ma), andPermian–Triassic extinction event(252 Ma) occur one after another: more than 80% of life on Earth becomes extinct in the lattermost, including mostretarianplankton, corals (TabulataandRugosadie out fully), brachiopods, bryozoans, gastropods, ammonoids (the goniatites die off fully), insects, parareptiles, synapsids, amphibians, and crinoids (onlyarticulatessurvived), and alleurypterids,trilobites,graptolites,hyoliths,edrioasteroid crinozoans,blastoidsandacanthodians.OuachitaandInnuitian orogeniesin North America.Uralian orogenyin Europe/Asia tapers off.Altaidorogeny in Asia.Hunter-Bowen OrogenyonAustralian continentbegins (c. 260–225 Ma), forming the New England Fold Belt.	254.14 ± 0.07*
				Wuchiapingian		259.51 ± 0.21*
			Guadalupian	Capitanian		264.28 ± 0.16*
				Wordian		266.9 ± 0.4*
				Roadian		273.01 ± 0.14*
			Cisuralian	Kungurian		283.5 ± 0.6
				Artinskian		290.1 ± 0.26*
				Sakmarian		293.52 ± 0.17*
				Asselian		298.9 ± 0.15*
		Carboniferous	Pennsylvanian	Gzhelian	Winged insectsradiate suddenly; some (esp.ProtodonataandPalaeodictyoptera) of them as well as somemillipedesandscorpionsbecome very large. Firstcoalforests (scale trees,ferns,club trees,giant horsetails,Cordaites,etc.). Higheratmosphericoxygenlevels.Ice Agecontinues to the Early Permian.Goniatites,brachiopods, bryozoa, bivalves, and corals plentiful in the seas and oceans. Firstwoodlice.Testateforamsproliferate.Euramericacollides withGondwanaand Siberia-Kazakhstania, the latter of which formsLaurasiaand theUralian orogeny.Variscan orogeny continues (these collisions created orogenies, and ultimatelyPangaea).Amphibians(e.g. temnospondyls) spread in Euramerica, with some becoming the firstamniotes.Carboniferous Rainforest Collapseoccurs, initiating a dry climate which favors amniotes over amphibians. Amniotes diversify rapidly intosynapsids,parareptiles,cotylosaurs,protorothyrididsanddiapsids.Rhizodontsremained common before they died out by the end of the period. Firstsharks.	303.7
Kasimovian				307 ± 0.1
Moscovian				315.2 ± 0.2
Bashkirian				323.2*
Mississippian			Serpukhovian	Largelycopodian primitive treesflourish and amphibiouseurypteridslive amidcoal-forming coastalswamps,radiating significantly one last time. Firstgymnosperms.Firstholometabolous,paraneopteran,polyneopteran,odonatopteranandephemeropteraninsects and firstbarnacles.First five-digitedtetrapods(amphibians) andland snails.In the oceans,bonyandcartilaginous fishesare dominant and diverse;echinoderms(especiallycrinoidsandblastoids) abundant.Corals,bryozoans,orthoceridans,goniatitesand brachiopods (Productida,Spiriferida,etc.) recover and become very common again, buttrilobitesandnautiloidsdecline.Glaciationin EastGondwanacontinues from Late Devonian.Tuhua Orogenyin New Zealand tapers off. Some lobe finned fish called rhizodonts become abundant and dominant in freshwaters.Siberiacollides with a different small continent,Kazakhstania.	330.9 ± 0.2
			Viséan		346.7 ± 0.4*
			Tournaisian		358.9 ± 0.4*
Devonian		Upper/Late	Famennian	Firstlycopods,ferns,seed plants(seed ferns,from earlierprogymnosperms), first trees (the progymnospermArchaeopteris), and firstwinged insects(palaeoptera and neoptera).Strophomenidandatrypidbrachiopods,rugoseandtabulatecorals, andcrinoidsare all abundant in the oceans. First fully coiled cephalopods (AmmonoideaandNautilida,independently) with the former group very abundant (especiallygoniatites). Trilobites and ostracoderms decline, while jawed fishes (placoderms,lobe-finnedandray-finnedbony fish,andacanthodiansand earlycartilaginous fish) proliferate. Somelobe finned fishtransform into digitedfishapods,slowly becoming amphibious. The last non-trilobite artiopods die off. Firstdecapods(likeprawns) andisopods.Pressure from jawed fishes cause eurypterids to decline andsome cephalopodsto lose their shells while anomalocarids vanish. "Old Red Continent" ofEuramericapersists after forming in the Caledonian orogeny. Beginning ofAcadian OrogenyforAnti-Atlas Mountainsof North Africa, andAppalachian Mountainsof North America, also theAntler,Variscan,andTuhua orogeniesin New Zealand. A series of extinction events, including the massiveKellwasserandHangenbergones, wipe out many acritarchs, corals, sponges, molluscs, trilobites, eurypterids, graptolites, brachiopods, crinozoans (e.g. allcystoids), and fish, including all placoderms and ostracoderms.	372.2 ± 1.6*
			Frasnian		382.7 ± 1.6*
		Middle	Givetian		387.7 ± 0.8*
			Eifelian		393.3 ± 1.2*
		Lower/Early	Emsian		407.6 ± 2.6*
			Pragian		410.8 ± 2.8*
			Lochkovian		419.2 ± 3.2*
Silurian		Pridoli		Ozone layerthickens. Firstvascular plantsand fully terrestrialised arthropods:myriapods,hexapods(includinginsects), andarachnids.Eurypteridsdiversify rapidly, becoming widespread and dominant. Cephalopods continue to flourish. Truejawed fishes,along withostracoderms,also roam the seas.Tabulateandrugosecorals,brachiopods(Pentamerida,Rhynchonellida,etc.),cystoidsandcrinoidsall abundant.Trilobitesandmolluscsdiverse;graptolitesnot as varied. Three minor extinction events. Some echinoderms go extinct. Beginning ofCaledonian Orogeny(collision between Laurentia, Baltica and one of the formerly small Gondwanan terranes) for hills in England, Ireland, Wales, Scotland, and theScandinavian Mountains.Also continued into Devonian period as theAcadian Orogeny,above (thus Euramerica forms).Taconic Orogenytapers off.Icehouse periodends late in this period after starting in Late Ordovician.Lachlan OrogenyonAustralian continenttapers off.	423 ± 2.3*
		Ludlow	Ludfordian		425.6 ± 0.9*
			Gorstian		427.4 ± 0.5*
		Wenlock	Homerian		430.5 ± 0.7*
			Sheinwoodian		433.4 ± 0.8*
		Llandovery	Telychian		438.5 ± 1.1*
			Aeronian		440.8 ± 1.2*
			Rhuddanian		443.8 ± 1.5*
Ordovician		Upper/Late	Hirnantian	TheGreat Ordovician Biodiversification Eventoccurs as plankton increase in number:invertebratesdiversify into many new types (especially brachiopods and molluscs; e.g. longstraight-shelledcephalopods like the long lasting and diverseOrthocerida). Earlycorals,articulatebrachiopods(Orthida,Strophomenida,etc.),bivalves,cephalopods(nautiloids),trilobites,ostracods,bryozoans,many types ofechinoderms(blastoids,cystoids,crinoids,sea urchins,sea cucumbers,andstar-like forms,etc.), branchedgraptolites,and other taxa all common.Acritarchsstill persist and common. Cephalopods become dominant and common, with some trending toward a coiled shell. Anomalocarids decline. Mysterioustentaculitansappear. Firsteurypteridsandostracodermfish appear, the latter probably giving rise to thejawed fishat the end of the period. First uncontroversial terrestrialfungiand fully terrestrialisedplants.Ice ageat the end of this period, as well as a series of massextinction events,killing off some cephalopods and many brachiopods, bryozoans, echinoderms, graptolites, trilobites, bivalves, corals andconodonts.	445.2 ± 1.4*
			Katian		453 ± 0.7*
			Sandbian		458.4 ± 0.9*
		Middle	Darriwilian		467.3 ± 1.1*
			Dapingian		470 ± 1.4*
		Lower/Early	Floian (formerlyArenig)		477.7 ± 1.4*
			Tremadocian		485.4 ± 1.9*
Cambrian		Furongian	Stage 10	Major diversification of (fossils mainly show bilaterian) life in theCambrian Explosionas oxygen levels increase. Numerous fossils; most modernanimalphyla(includingarthropods,molluscs,annelids,echinoderms,hemichordatesandchordates) appear. Reef-buildingarchaeocyathansponges initially abundant, then vanish. Stromatolites replace them, but quickly fall prey to theAgronomic revolution,when some animals started burrowing through the microbial mats (affecting some other animals as well). Firstartiopods(includingtrilobites),priapulidworms, inarticulatebrachiopods(unhinged lampshells),hyoliths,bryozoans,graptolites,pentaradial echinoderms (e.g.blastozoans,crinozoansandeleutherozoans), and numerous other animals.Anomalocaridsare dominant and giant predators, whilemany Ediacaran fauna die out.Crustaceansand molluscs diversify rapidly.Prokaryotes,protists(e.g.,forams),algaeandfungicontinue to present day. Firstvertebratesfrom earlier chordates.Petermann Orogenyon theAustralian continenttapers off (550–535 Ma). Ross Orogeny in Antarctica.Delamerian Orogeny(c. 514–490 Ma) onAustralian continent.Some small terranes split off from Gondwana.AtmosphericCO2content roughly 15 times present-day (Holocene) levels (6000 ppm compared to today's 400 ppm)Arthropodsandstreptophytastart colonising land. 3 extinction events occur 517, 502 & 488 Ma, thefirstandlastof which wipe out many of the anomalocarids, artiopods, hyoliths, brachiopods, molluscs, and conodonts (early jawless vertebrates).	~489.5
			Jiangshanian		~494*
			Paibian		~497*
		Miaolingian	Guzhangian		~500.5*
			Drumian		~504.5*
			Wuliuan		~509
		Series 2	Stage 4		~514
			Stage 3		~521
		Terreneuvian	Stage 2		~529
			Fortunian		538.8 ± 0.2*
Proterozoic	Neoproterozoic	Ediacaran	Goodfossilsof primitiveanimals.Ediacaran biotaflourish worldwide in seas, possibly appearing after anexplosion,possibly caused by a large-scale oxidation event.Firstvendozoans(unknown affinity among animals),cnidariansandbilaterians.Enigmatic vendozoans include many soft-jellied creatures shaped like bags, disks, or quilts (likeDickinsonia). Simpletrace fossilsof possible worm-likeTrichophycus,etc.Taconic Orogenyin North America.Aravalli RangeorogenyinIndian subcontinent.Beginning ofPan-African Orogeny,leading to the formation of the short-lived Ediacaran supercontinentPannotia,which by the end of the period breaks up intoLaurentia,Baltica,SiberiaandGondwana.Petermann Orogenyforms onAustralian continent.Beardmore Orogeny in Antarctica, 633–620 Ma.Ozone layerforms. An increase in oceanicminerallevels.			~635*
		Cryogenian	Possible "Snowball Earth"period.Fossilsstill rare. Late Ruker / Nimrod Orogeny in Antarctica tapers off. First uncontroversialanimalfossils. First hypotheticalterrestrial fungiandstreptophyta.			~720
		Tonian	Final assembly ofRodiniasupercontinent occurs in early Tonian, with breakup beginning c. 800 Ma.Sveconorwegian orogenyends.Grenville Orogenytapers off in North America. Lake Ruker / Nimrod Orogeny in Antarctica, 1,000 ± 150 Ma. Edmundian Orogeny (c. 920–850 Ma),Gascoyne Complex,Western Australia. Deposition ofAdelaide SuperbasinandCentralian Superbasinbegins onAustralian continent.First hypotheticalanimals(from holozoans) and terrestrial algal mats. Many endosymbiotic events concerning red and green algae occur, transferring plastids toochrophyta(e.g.diatoms,brown algae),dinoflagellates,cryptophyta,haptophyta,andeuglenids(the events may have begun in the Mesoproterozoic)while the firstretarians(e.g.forams) also appear: eukaryotes diversify rapidly, including algal, eukaryovoric andbiomineralisedforms.Trace fossilsof simplemulti-celledeukaryotes.			1000
	Mesoproterozoic	Stenian	Narrow highlymetamorphicbelts due toorogenyasRodiniaforms, surrounded by thePan-African Ocean.Sveconorwegian orogenystarts. Late Ruker / Nimrod Orogeny in Antarctica possibly begins. Musgrave Orogeny (c. 1,080–),Musgrave Block,Central Australia.Stromatolitesdecline asalgaeproliferate.			1200
		Ectasian	Platform coverscontinue to expand.Algalcoloniesin the seas.Grenville Orogenyin North America. Columbia breaks up.			1400
		Calymmian	Platform coversexpand. Barramundi Orogeny,McArthur Basin,Northern Australia,and Isan Orogeny,c.1,600 Ma, Mount Isa Block, Queensland. Firstarchaeplastidans(the first eukaryotes withplastidsfrom cyanobacteria; e.g.redandgreen algae) andopisthokonts(giving rise to the firstfungiandholozoans).Acritarchs(remains of marine algae possibly) start appearing in the fossil record.			1600
	Paleoproterozoic	Statherian	First uncontroversialeukaryotes:protistswith nuclei and endomembrane system.Columbiaforms as the second undisputed earliest supercontinent. Kimban Orogeny in Australian continent ends. Yapungku Orogeny onYilgarn craton,in Western Australia. Mangaroon Orogeny, 1,680–1,620 Ma, on theGascoyne Complexin Western Australia. Kararan Orogeny (1,650 Ma), Gawler Craton,South Australia.Oxygen levels drop again.			1800
		Orosirian	Theatmospherebecomes much moreoxygenicwhile more cyanobacterial stromatolites appear.VredefortandSudbury Basinasteroid impacts. Muchorogeny.PenokeanandTrans-Hudsonian Orogeniesin North America. Early Ruker Orogeny in Antarctica, 2,000–1,700 Ma. Glenburgh Orogeny,Glenburgh Terrane,Australian continentc.2,005–1,920 Ma. Kimban Orogeny,Gawler cratonin Australian continent begins.			2050
		Rhyacian	Bushveld Igneous Complexforms.Huronianglaciation. First hypotheticaleukaryotes.MulticellularFrancevillian biota.Kenorland disassembles.			2300
		Siderian	Great Oxidation Event(due tocyanobacteria) increases oxygen. Sleaford Orogeny onAustralian continent,Gawler Craton2,440–2,420 Ma.			2500
Archean	Neoarchean	Stabilization of most moderncratons;possiblemantleoverturn event. Insell Orogeny, 2,650 ± 150 Ma.Abitibi greenstone beltin present-dayOntarioandQuebecbegins to form, stabilises by 2,600 Ma. First uncontroversialsupercontinent,Kenorland,and first terrestrialprokaryotes.				2800
	Mesoarchean	Firststromatolites(probablycolonialphototrophic bacteria, like cyanobacteria). Oldestmacrofossils.Humboldt Orogeny in Antarctica.Blake River Megacaldera Complexbegins to form in present-dayOntarioandQuebec,ends by roughly 2,696 Ma.				3200
	Paleoarchean	Prokaryoticarchaea(e.g.methanogens) andbacteria(e.g.cyanobacteria) diversify rapidly, along with earlyviruses.First knownphototrophicbacteria.Oldest definitivemicrofossils.Firstmicrobial mats.Oldestcratonson Earth (such as theCanadian Shieldand thePilbara Craton) may have formed during this period.Rayner Orogeny in Antarctica.				3600
	Eoarchean	First uncontroversialliving organisms:at firstprotocellswithRNA-based genesaround 4000 Ma, after which truecells(prokaryotes) evolve along withproteinsandDNA-based genes around 3800 Ma. The end of theLate Heavy Bombardment.NapierOrogeny in Antarctica, 4,000 ± 200 Ma.				4031
Hadean	Formation ofprotolithof the oldest known rock (Acasta Gneiss) c. 4,031 to 3,580 Ma.Possible first appearance ofplate tectonics.First hypotheticallife forms.End of the Early Bombardment Phase. Oldest knownmineral(Zircon,4,404 ± 8 Ma).Asteroids and comets bring water to Earth, forming the first oceans. Formation ofMoon(4,510 Ma), probably from agiant impact.Formation of Earth (4,543 to 4,540 Ma)					4567.3 ± 0.16

Non-Earth based geologic time scales

Main articles:Lunar geologic timescale,Martian geologic timescale,andGeology of Venus

Some otherplanetsandsatellitesin theSolar Systemhave sufficiently rigid structures to have preserved records of their own histories, for example,Venus,Marsand the Earth'sMoon.Dominantly fluid planets, such as thegiant planets,do not comparably preserve their history. Apart from theLate Heavy Bombardment,events on other planets probably had little direct influence on the Earth, and events on Earth had correspondingly little effect on those planets. Construction of a time scale that links the planets is, therefore, of only limited relevance to the Earth's time scale, except in a Solar System context. The existence, timing, and terrestrial effects of the Late Heavy Bombardment are still a matter of debate.

Lunar (selenological) time scale

Thegeologic historyof Earth's Moon has been divided into a time scale based ongeomorphologicalmarkers, namelyimpact cratering,volcanism,anderosion.This process of dividing the Moon's history in this manner means that the time scale boundaries do not imply fundamental changes in geological processes, unlike Earth's geologic time scale. Five geologic systems/periods (Pre-Nectarian,Nectarian,Imbrian,Eratosthenian,Copernican), with the Imbrian divided into two series/epochs (Early and Late) were defined in the latest Lunar geologic time scale.The Moon is unique in the Solar System in that it is the only other body from which we have rock samples with a known geological context.

Millions of years before present

Martian geologic time scale

Thegeological history of Marshas been divided into two alternate time scales. The first time scale for Mars was developed by studying the impact crater densities on the Martian surface. Through this method four periods have been defined, the Pre-Noachian (~4,500–4,100 Ma), Noachian (~4,100–3,700 Ma), Hesperian (~3,700–3,000 Ma), and Amazonian (~3,000 Ma to present).

Martian time periods (millions of years ago)

Epochs:

A second time scale based on mineral alteration observed by the OMEGAspectrometeron board theMars Express.Using this method, three periods were defined, the Phyllocian (~4,500–4,000 Ma), Theiikian (~4,000–3,500 Ma), and Siderikian (~3,500 Ma to present).

See also

• Age of the Earth
• Cosmic calendar
• Deep time
• Evolutionary history of life
• Formation and evolution of the Solar System
• Geological history of Earth
• Geology of Mars
• Geon (geology)
• Graphical timeline of the universe
• History of Earth
• History of geology
• History of paleontology
• List of fossil sites
• List of geochronologic names
• Logarithmic timeline
• Lunar geologic timescale
• Martian geologic timescale
• Natural history
• New Zealand geologic time scale
• Prehistoric life
• Timeline of the Big Bang
• Timeline of evolution
• Timeline of the geologic history of the United States
• Timeline of human evolution
• Timeline of natural history
• Timeline of paleontology

Further reading

• Aubry, Marie-Pierre; Van Couvering, John A.; Christie-Blick, Nicholas; Landing, Ed; Pratt, Brian R.; Owen, Donald E.; Ferrusquia-Villafranca, Ismael (2009). "Terminology of geological time: Establishment of a community standard".Stratigraphy.6(2): 100–105.doi:10.7916/D8DR35JQ.
• Gradstein, F. M.; Ogg, J. G. (2004)."A Geologic Time scale 2004 – Why, How and Where Next!"(PDF).Lethaia.37(2): 175–181.Bibcode:2004Letha..37..175G.doi:10.1080/00241160410006483.Archived fromthe original(PDF)on 17 April 2018.Retrieved30 November2018.
• Gradstein, Felix M.; Ogg, James G.; Smith, Alan G. (2004).A Geologic Time Scale 2004.Cambridge, UK: Cambridge University Press.ISBN978-0-521-78142-8.Retrieved18 November2011.
• Gradstein, Felix M.; Ogg, James G.; Smith, Alan G.; Bleeker, Wouter; Laurens, Lucas, J. (June 2004)."A new Geologic Time Scale, with special reference to Precambrian and Neogene".Episodes.27(2): 83–100.doi:10.18814/epiiugs/2004/v27i2/002.{{cite journal}}:CS1 maint: multiple names: authors list (link)
• Ialenti, Vincent (28 September 2014)."Embracing 'Deep Time' Thinking".NPR.NPR Cosmos & Culture.
• Ialenti, Vincent (21 September 2014)."Pondering 'Deep Time' Could Inspire New Ways To View Climate Change".NPR.NPR Cosmos & Culture.
• Knoll, Andrew H.;Walter, Malcolm R.; Narbonne, Guy M.; Christie-Blick, Nicholas (30 July 2004)."A New Period for the Geologic Time Scale"(PDF).Science.305(5684): 621–622.doi:10.1126/science.1098803.PMID15286353.S2CID32763298.Archived(PDF)from the original on 15 December 2011.Retrieved18 November2011.
• Levin, Harold L. (2010)."Time and Geology".The Earth Through Time.Hoboken, New Jersey: John Wiley & Sons.ISBN978-0-470-38774-0.Retrieved18 November2011.
• Montenari, Michael (2016).Stratigraphy and Timescales(1st ed.). Amsterdam: Academic Press (Elsevier).ISBN978-0-12-811549-7.
• Montenari, Michael (2017).Advances in Sequence Stratigraphy(1st ed.). Amsterdam: Academic Press (Elsevier).ISBN978-0-12-813077-3.
• Montenari, Michael (2018).Cyclostratigraphy and Astrochronology(1st ed.). Amsterdam: Academic Press (Elsevier).ISBN978-0-12-815098-6.
• Montenari, Michael (2019).Case Studies in Isotope Stratigraphy(1st ed.). Amsterdam: Academic Press (Elsevier).ISBN978-0-12-817552-1.
• Montenari, Michael (2020).Carbon Isotope Stratigraphy(1st ed.). Amsterdam: Academic Press (Elsevier).ISBN978-0-12-820991-2.
• Montenari, Michael (2021).Calcareous Nannofossil Biostratigraphy(1st ed.). Amsterdam: Academic Press (Elsevier).ISBN978-0-12-824624-5.
• Nichols, Gary (2013).Sedimentology and Stratigraphy(2nd ed.). Hoboken: Wiley-Blackwell.ISBN978-1-4051-3592-4
• Williams, Aiden (2019).Sedimentology and Stratigraphy(1st ed.). Forest Hills, NY: Callisto Reference.ISBN978-1-64116-075-9

External links

• The current version of the International Chronostratigraphic Chart can be found atstratigraphy.org/chart
• Interactive version of the International Chronostratigraphic Chart is found atstratigraphy.org/timescale
• A list of current Global Boundary Stratotype and Section Points is found atstratigraphy.org/gssps
• NASA: Geologic Time(archived 18 April 2005)
• GSA: Geologic Time Scale(archived 20 January 2019)
• British Geological Survey: Geological Timechart
• GeoWhen Database(archived 23 June 2004)
• National Museum of Natural History – Geologic Time(archived 11 November 2005)
• SeeGrid: Geological Time Systems.Archived23 July 2008 at theWayback Machine.Information model for the geologic time scale.
• Exploring Timefrom Planck Time to the lifespan of the universe
• Episodes,Gradstein, Felix M. et al. (2004)A new Geologic Time Scale, with special reference to Precambrian and Neogene,Episodes, Vol. 27, no. 2 June 2004 (pdf)
• Lane, Alfred C, and Marble, John Putman 1937.Report of the Committee on the measurement of geologic time
• Lessons for Children on Geologic Time(archived 14 July 2011)
• Deep Time – A History of the Earth: Interactive Infographic
• Geology Buzz: Geologic Time Scale.Archived12 August 2021 at theWayback Machine.