Geologic time scale

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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 the 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 Proterozoic are both eons, the Palaeozoic, Mesozoic and Cenozoic are eras of the Phanerozoic eon. The three million year Quaternary period, the time of recognizable humans, is too small to be visible at this scale.

The geologic time scale (GTS) is a system of chronological dating that classifies geological strata (stratigraphy) in time. It is used by geologists, paleontologists, and other Earth scientists to describe the timing and relationships of events in geologic history. The time scale was developed through the study and observation of layers of rock and relationships as well as the times when different organisms appeared, evolved and became extinct through the study of fossilized remains and imprints. The table of geologic time spans, presented here, agrees with the nomenclature, dates and standard color codes set forth by the International Commission on Stratigraphy (ICS).

Terminology[]

The largest catalogued divisions of time are intervals called eons. The first eon was the Hadean, starting with the formation of the Earth and lasting about 540 million years until the Archean eon, which is when the Earth had cooled enough for continents and the earliest known life to emerge. After about 2.5 billion years, oxygen generated by photosynthesizing single-celled organisms began to appear in the atmosphere marking the beginning of the Proterozoic. Finally, the Phanerozoic eon encompasses 541 million years of diverse abundance of multicellular life starting with the appearance of hard animal shells in the fossil record and continuing to the present. The first three eons (i.e. every eon but the Phanerozoic) can be referred to collectively as the Precambrian supereon. This is because of the significance of the Cambrian Explosion, a massive diversification of multi-cellular life forms that took place in the Cambrian period at the start of the Phanerozoic. Eons are divided into eras,[2] which are in turn divided into periods,[3] epochs and ages. A polarity chron or just "chron" can be used as a subdivision of an age, though this is not included in the ICS system.

Eon Era Period Extent, Million
Years Ago 		Duration, Millions
of Years
Phanerozoic Cenozoic Quaternary (Pleistocene/Holocene) 2.588–0 2.588+
Neogene (Miocene/Pliocene) 23.03–2.588 20.4
Paleogene (Paleocene/Eocene/Oligocene) 66.0–23.03 42.9
Mesozoic Cretaceous 145.5–66.0 79.5
Jurassic 201.3–145.0 56.3
Triassic 252.17–201.3 50.9
Paleozoic Permian 298.9–252.17 46.7
Carboniferous (Mississippian/Pennsylvanian) 358.9–298.9 60
Devonian 419.2–358.9 60.3
Silurian 443.4–419.2 24.2
Ordovician 485.4–443.4 42
Cambrian 541.0–485.4 55.6
Proterozoic Neoproterozoic Ediacaran 635.0–541.0 94
Cryogenian 720–635 85
Tonian 1000–720 280
Mesoproterozoic Stenian 1200–1000 200
Ectasian 1400–1200 200
Calymmian 1600–1400 200
Paleoproterozoic Statherian 1800–1600 200
Orosirian 2050–1800 250
Rhyacian 2300–2050 250
Siderian 2500–2300 200
Archean Neoarchean not officially divided into periods 2,800 to 2,500 million years ago 300
Mesoarchean 3,200 to 2,800 million years ago 400
Paleoarchean 3,600 to 3,200 million years ago 400
Eoarchean 4,000 to 3,600 million years ago 400
Hadean not officially divided into eras not officially divided into periods Formation of Earth to 4,000 million years ago 540
Units in geochronology and stratigraphy[4]
Segments of rock (strata) in chronostratigraphy Time spans in geochronology Notes to
geochronological units
Eonothem Eon 4 total, half a billion years or more
Erathem Era 10 defined, several hundred million years
System Period 22 defined, tens to ~one hundred million years
Series Epoch 34 defined, tens of millions of years
Stage Age 99 defined, millions of years
Chronozone Chron subdivision of an age, not used by the ICS timescale
Visual timelines including ages

The following five timelines show the geologic time 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. Therefore, 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.

SiderianRhyacianOrosirianStatherianCalymmianEctasianStenianTonianCryogenianEdiacaranEoarcheanPaleoarcheanMesoarcheanNeoarcheanPaleoproterozoicMesoproterozoicNeoproterozoicPaleozoicMesozoicCenozoicHadeanArcheanProterozoicPhanerozoicPrecambrian
CambrianOrdovicianSilurianDevonianCarboniferousPermianTriassicJurassicCretaceousPaleogeneNeogeneQuaternaryPaleozoicMesozoicCenozoicPhanerozoic
PaleoceneEoceneOligoceneMiocenePliocenePleistoceneHolocenePaleogeneNeogeneQuaternaryCenozoic
GelasianCalabrian (stage)ChibanianPleistocenePleistoceneHoloceneQuaternary
GreenlandianNorthgrippianMeghalayanHolocene
Millions of Years (1st, 2nd, 3rd, and 4th)
Thousands of years (5th)

Corresponding to eons, eras, periods, epochs and ages, the terms "eonothem", "erathem", "system", "series", "stage" are used to refer to the layers of rock that belong to these stretches of geologic time in Earth's history.

Geologists qualify these units as "early", "mid", and "late" when referring to time, and "lower", "middle", and "upper" when referring to the corresponding rocks. For example, the Lower Jurassic Series in chronostratigraphy corresponds to the Early Jurassic Epoch in geochronology.[5] The adjectives are capitalized when the subdivision is formally recognized, and lower case when not; thus "early Miocene" but "Early Jurassic."

Era definitions[]

The Phanerozoic Eon is divided into three eras: the Paleozoic, Mesozoic, and Cenozoic (meaning "old life", "middle life" and "recent life") that represent the major stages in the macroscopic fossil record. These eras are separated by catastrophic extinction boundaries: the P-T boundary between the Paleozoic and the Mesozoic, and the K-Pg boundary between the Mesozoic and the Cenozoic.[6] There is evidence that the P-T boundary was caused by the eruption of the Siberian Traps, and the K-Pg boundary was caused by the meteorite impact that created the Chicxulub crater.[citation needed]

The Hadean, Archean and Proterozoic eons were as a whole formerly called the Precambrian. This covered the four billion years of Earth history prior to the appearance of hard-shelled animals. More recently, however, the Archean and Proterozoic eons have been subdivided into eras of their own.

Period definitions[]

The twelve currently recognised periods of the present eon – the Phanerozoic – are defined by the International Commission on Stratigraphy (ICS) by reference to the stratigraphy at particular locations around the world.[7] In 2004 the Ediacaran Period of the latest Precambrian was defined in similar fashion, and was the first such newly designated period in 130 years.[8]

A consequence of this approach to the Phanerozoic periods is that the ages of their beginnings and ends can change from time to time as the absolute age of the chosen rock sequences, which define them, is more precisely determined.[9]

The set of rocks (sedimentary, igneous or metamorphic) formed during a period belong to a chronostratigraphic unit called a system.[10] For example, the "Jurassic System" of rocks was formed during the "Jurassic Period" (between 201 and 145 million years ago).[10]

Principles[]

Evidence from radiometric dating indicates that Earth is about 4.54 billion years old.[11][12] The geology or deep time of Earth's past has been organized into various units according to events that are thought to have taken place. Different spans of time on the GTS are usually marked by corresponding changes in the composition of strata which indicate major geological or paleontological events, such as mass extinctions. For example, the boundary between the Cretaceous period and the Paleogene period is defined by the Cretaceous–Paleogene extinction event, which marked the demise of the non-avian dinosaurs as well as many other groups of life. Older time spans, which predate the reliable fossil record (before the Proterozoic eon), are defined by their absolute age.

Geologic units from the same time but different parts of the world often are not similar and contain different fossils, so the same time-span was historically given different names in different locales. For example, in North America, the Lower Cambrian is called the Waucoban series that is then subdivided into zones based on the succession of trilobites. In East Asia and Siberia, the same unit is split into Alexian, Atdabanian, and Botomian stages. A key aspect of the work of the International Commission on Stratigraphy is to reconcile this conflicting terminology and define universal horizons that can be used around the world.[13]

Some other planets and moons in the Solar System have sufficiently rigid structures to have preserved records of their own histories, for example, Venus, Mars and the Earth's Moon. Dominantly fluid planets, such as the gas giants, do not comparably preserve their history. Apart from the Late 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.[a]

History and nomenclature of the time scale[]

Main articles: History of geology and History of paleontology
Graphical representation of Earth's history as a spiral

Early history[]

In Ancient Greece, Aristotle (384–322 BCE) observed that fossils of seashells in rocks resembled those found on beaches – he inferred that the fossils in rocks were formed by organisms, and he reasoned that the positions of land and sea had changed over long periods of time. Leonardo da Vinci (1452–1519) concurred with Aristotle's interpretation that fossils represented the remains of ancient life.[14]

The 11th-century Persian polymath Avicenna (Ibn Sina, died 1037) and the 13th-century Dominican bishop Albertus Magnus (died 1280) extended Aristotle's explanation into a theory of a petrifying fluid.[15] Avicenna also first proposed one of the principles underlying geologic time scales, the law of superposition of strata, while discussing the origins of mountains in The Book of Healing (1027).[16] The Chinese naturalist Shen Kuo (1031–1095) also recognized the concept of "deep time".[17]

Establishment of primary principles[]

In the late 17th century Nicholas Steno (1638–1686) pronounced the principles underlying geologic (geological) time scales. Steno argued that rock layers (or strata) were laid down in succession and that each represents a "slice" of time. He also formulated the law of superposition, which states that any given stratum is probably older than those above it and younger than those below it. While Steno's principles were simple, applying them proved challenging. Steno's ideas also lead to other important concepts geologists use today, such as relative dating. Over the course of the 18th-century geologists realized that:

  1. Sequences of strata often become 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 Earth's long history

The Neptunist theories popular at this time (expounded by Abraham Werner (1749–1817) in the late 18th century) proposed that all rocks had precipitated out of a single enormous flood. A major shift in thinking came when James Hutton presented his Theory of the Earth; or, an Investigation of the Laws Observable in the Composition, Dissolution, and Restoration of Land Upon the Globe[18] before the Royal Society of Edinburgh in March and April 1785. John McPhee asserts that "as things appear from the perspective of the 20th century, James Hutton in those readings became the founder of modern geology".[19]: 95–100  Hutton proposed that the interior of Earth was hot and that this heat was the engine which drove the creation of new rock: land was eroded by air and water and deposited as layers in the sea; heat then consolidated the sediment into stone and uplifted it into new lands. This theory, known as "Plutonism", stood in contrast to the "Neptunist" flood-oriented theory.

Formulation of geologic time scale[]

The first serious attempts to formulate a geologic time scale that could be applied anywhere on Earth were made in the late 18th century. The most influential of those early attempts (championed by Werner, among others) divided the rocks of 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" (now Paleogene and Neogene) remained in use as the name of a geological period well into the 20th century and "Quaternary" remains in formal use as the name of the current period.

The identification of strata by the fossils they contained, pioneered by William Smith, Georges Cuvier, Jean d'Omalius d'Halloy, and Alexandre Brongniart in the early 19th century, enabled geologists to divide Earth history more 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 between 1820 and 1850 of the strata and fossils of Europe produced the sequence of geologic periods still used today.

Naming of geologic periods, eras and epochs[]

Early work on developing the geologic time scale was dominated by British geologists, and the names of the geologic periods reflect that dominance. The "Cambrian", (the classical name for Wales) and the "Ordovician" and "Silurian", named after ancient Welsh tribes, were periods defined using stratigraphic sequences from Wales.[19]: 113–114  The "Devonian" was named for the English county of Devon, and the name "Carboniferous" was an adaptation of "the Coal Measures", the old British geologists' term for the same set of strata. The "Permian" was named after the region of Perm in Russia, because it was defined using strata in that region by Scottish geologist Roderick Murchison. However, some periods were defined by geologists from other countries. The "Triassic" was named in 1834 by a German geologist Friedrich Von Alberti from the three distinct layers (Latin trias meaning triad) – red beds, capped by chalk, followed by black shales – that are found throughout Germany and Northwest Europe, called the ‘Trias’. The "Jurassic" was named by a French geologist Alexandre Brongniart for the extensive marine limestone exposures of the Jura Mountains. The "Cretaceous" (from Latin creta meaning ‘chalk’) as a separate period was first defined by Belgian geologist Jean d'Omalius d'Halloy in 1822, using strata in the Paris basin[20] and named for the extensive beds of chalk (calcium carbonate deposited by the shells of marine invertebrates) found in Western Europe.

British geologists were also responsible for the grouping of periods into eras and the subdivision of the Tertiary and Quaternary periods into epochs. In 1841 John Phillips published the first global geologic time scale based on the types of fossils found in each era. Phillips' scale helped standardize the use of terms like Paleozoic ("old life"), which he extended to cover a larger period than it had in previous usage, and Mesozoic ("middle life"), which he invented.[21]

Dating of time scales[]

Main article: Chronological dating

When William Smith and Sir Charles Lyell first recognized that rock strata represented successive time periods, time scales could be estimated only very imprecisely since estimates of rates of change were uncertain. While creationists had been proposing dates of around six or seven thousand years for the age of Earth based on the Bible, early geologists were suggesting millions of years for geologic periods, and some were even suggesting a virtually infinite age for Earth.[citation needed] Geologists and paleontologists constructed the geologic table based on the relative positions of different strata and fossils, and estimated the time scales based on studying rates of various kinds of weathering, erosion, sedimentation, and lithification. Until the discovery of radioactivity in 1896 and the development of its geological applications through radiometric dating during the first half of the 20th century, the ages of various rock strata and the age of Earth were the subject of considerable debate.

The first geologic time scale that included absolute dates was published in 1913 by the British geologist Arthur Holmes.[22] He greatly furthered the newly created discipline of geochronology and published the world-renowned book The Age of the Earth in which he estimated Earth's age to be at least 1.6 billion years.[23]

In a steady effort ongoing since 1974, the International Commission on Stratigraphy has been working to correlate the world's local stratigraphic record into one uniform planet-wide benchmarked system.[24]

In 1977, the Global Commission on Stratigraphy (now the International Commission on Stratigraphy) began to define global references known as GSSP (Global Boundary Stratotype Sections and Points) for geologic periods and faunal stages. The commission's work is described in the 2012 geologic time scale of Gradstein et al.[9] A UML model for how the timescale is structured, relating it to the GSSP, is also available.[25]

Correlation issues[]

American geologists have long considered the Mississippian and Pennsylvanian to be periods in their own right though the ICS now recognises them both as "subperiods" of the Carboniferous Period recognised by European geologists.[26] Cases like this in China, Russia and even New Zealand with other geological eras has slowed the uniform organization of the stratigraphic record.[27]

The Anthropocene[]

Popular culture and a growing number of scientists use the term "Anthropocene" informally to label the current epoch in which we are living.[28] The term was coined by Paul Crutzen and Eugene Stoermer in 2000 to describe the current time in which humans have had an enormous impact on the environment. It has evolved to describe an "epoch" starting some time in the past and on the whole defined by anthropogenic carbon emissions and production and consumption of plastic goods that are left in the ground.[29]

Critics of this term say that the term should not be used because it is difficult, if not nearly impossible, to define a specific time when humans started influencing the rock strata – defining the start of an epoch.[30]

The ICS has not officially approved the term as of September 2015.[31] The Anthropocene Working Group met in Oslo in April 2016 to consolidate evidence supporting the argument for the Anthropocene as a true geologic epoch.[31] Evidence was evaluated and the group voted to recommend "Anthropocene" as the new geological age in August 2016.[32] Should the International Commission on Stratigraphy approve the recommendation, the proposal to adopt the term will have to be ratified by the International Union of Geological Sciences before its formal adoption as part of the geologic time scale.[33]

Notable period changes[]

  • Changes in recent years have included the abandonment of the former Tertiary Period in favour of the Paleogene and succeeding Neogene periods. This remains controversial.[34]
  • The abandonment of the Quaternary period was also considered but it has been retained for continuity reasons.[35]
  • Even earlier in the history of the science, the Tertiary was considered to be an "era" and its subdivisions (Paleocene, Eocene, Oligocene, Miocene and Pliocene) were themselves referred to as "periods"[36] but they now enjoy the status of "epochs" within the more recently delineated Paleogene and Neogene periods.[7]

Table of geologic time[]

The following table summarizes the major events and characteristics of the periods of time making up the geologic time scale. 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.

The content of the table is based on the current official geologic time scale of the International Commission on Stratigraphy (ICS),[1] with the epoch names altered to the early/late format from lower/upper as recommended by the ICS when dealing with chronostratigraphy.[5]

The ICS provides an online interactive version of this chart, ics-chart, based on a service delivering a machine-readable Resource Description Framework/Web Ontology Language representation of the timescale, which is available through the Commission for the Management and Application of Geoscience Information GeoSciML project as a service[37] and at a SPARQL end-point.[38][39]

This is not to scale, and even though the Phanerozoic eon looks longer than the rest, it merely spans 500 million years, whilst the previous three eons (or the Precambrian supereon) collectively span over 3.5 billion years. This bias toward the most recent eon is due to the relative lack of information about events that occurred during the first three eons (or supereon) compared to the current eon (the Phanerozoic).[citation needed]

The proposed Anthropocene epoch is not included.

Supereon Eon Era Period[b] Epoch Age[c] Major events Start, million years ago[c]
n/a[d] Phanerozoic Cenozoic[e] Quaternary Holocene Meghalayan 4.2 kiloyear event, Little Ice Age, increasing industrial CO2. 0.0042*
Northgrippian 8.2 kiloyear event, Holocene climatic optimum. Bronze Age. 0.0082*
Greenlandian Current interglacial begins. Sea level flooding of Doggerland and Sundaland. Sahara desert forms. Neolithic agriculture. 0.0117*
Pleistocene Late ('Tarantian') Eemian interglacial, Last glacial period, ending with Younger Dryas. Toba eruption. Megafauna extinction. 0.129
Chibanian High amplitude 100 ka glacial cycles. Rise of Homo sapiens. 0.774
Calabrian Further cooling of the climate. Spread of Homo erectus. 1.8*
Gelasian Start of Quaternary glaciations. Rise of the Pleistocene megafauna and Homo habilis. 2.58*
Neogene Pliocene Piacenzian Greenland ice sheet develops.[42] Australopithecus common in East Africa.[43] 3.6*
Zanclean Zanclean flooding of the Mediterranean Basin. Cooling climate. Ardipithecus in Africa.[43] 5.333*
Miocene Messinian Messinian Event with hypersaline lakes in empty Mediterranean Basin. Moderate Icehouse climate, punctuated by ice ages and re-establishment of East Antarctic Ice Sheet; Gradual separation of human and chimpanzee ancestors. Sahelanthropus tchadensis in Africa. 7.246*
Tortonian 11.63*
Serravallian Warmer during middle Miocene climate optimum.[44] Extinctions in middle Miocene disruption. 13.82*
Langhian 15.97
Burdigalian Orogeny in Northern Hemisphere. Start of Kaikoura Orogeny forming Southern Alps in New Zealand. Widespread forests slowly draw in massive amounts of CO2, gradually lowering the level of atmospheric CO2 from 650 ppmv down to around 100 ppmv during the Miocene.[45][f] Modern mammal and bird families become recognizable. Horses and mastodons diverse. Grasses become ubiquitous. Ancestor of apes, including humans.[46] 20.44
Aquitanian 23.03*
Paleogene Oligocene Chattian Grande Coupure extinction. Start of widespread Antarctic glaciation.[47] Rapid evolution and diversification of fauna, especially mammals. Major evolution and dispersal of modern types of flowering plants 28.1
Rupelian 33.9*
Eocene Priabonian Moderate, cooling climate. 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. Reglaciation of Antarctica and formation of its ice cap; End of Laramide and Sevier Orogenies of the Rocky Mountains in North America. Orogeny of the Alps in Europe begins. Hellenic Orogeny begins in Greece and Aegean Sea. 37.8
Bartonian 41.2
Lutetian 47.8*
Ypresian Two transient events of global warming (PETM and ETM-2) and warming climate until the Eocene Climatic Optimum. The Azolla event decreased CO2 levels from 3500 ppm to 650 ppm, setting the stage for a long period of cooling.[45][f] Indian subcontinent collides with Asia and starts Himalayan Orogeny. 56*
Paleocene Thanetian Starts with Chicxulub impact and the K-Pg extinction event. Climate tropical. Modern plants appear; Mammals diversify into a number of lineages following the extinction of the non-avian dinosaurs. First large mammals (up to bear or small hippo size). Alpine orogeny in Europe and Asia begins. Birds diversify rapidly. First primates appear. 59.2*
Selandian 61.6*
Danian 66*
Mesozoic Cretaceous Late Maastrichtian Flowering plants proliferate, along with new types of insects. More modern teleost fish begin to appear. Ammonoidea, belemnites, rudist bivalves, echinoids and sponges all common. Many new types of dinosaurs (e.g. Tyrannosaurs, Titanosaurs, Hadrosaurs, and Ceratopsids) evolve on land, while crocodilians) appear in water; and mosasaurs and modern sharks appear in the sea. Toothed and toothless birds coexist with pterosaurs. Modern monotremes, marsupials and placental mammals appear. Break up of Gondwana. Beginning of Laramide and Sevier Orogenies of the Rocky Mountains. Atmospheric CO2 close to present-day levels. 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*
Early Albian ~113
Aptian ~125
Barremian ~129.4
Hauterivian ~132.9
Valanginian ~139.8
Berriasian ~145
Jurassic Late Tithonian Gymnosperms (especially conifers, Bennettitales and cycads) and ferns common. Dinosaurs, including sauropods, carnosaurs, and stegosaurs, become the dominant land vertebrates. Mammals diversify into australosphenidans and therians but mostly remain small. First birds, lizards and snakes. Ichthyosaurs and plesiosaurs diverse. Bivalves, Ammonites and belemnites abundant. Sea urchins very common, along with crinoids, starfish, sponges, and terebratulid and rhynchonellid brachiopods. Breakup of Pangaea into Gondwana and Laurasia. Nevadan orogeny in North America. Rangitata and Cimmerian orogenies taper off. Atmospheric CO2 levels 3–4 times the present day levels (1200–1500 ppmv, compared to today's 400 ppmv[45][f]). Crocodylomorphs seek out an aquatic lifestyle. 152.1 ± 0.9
Kimmeridgian 157.3 ± 1.0
Oxfordian 163.5 ± 1.0
Middle Callovian 166.1 ± 1.2
Bathonian 168.3 ± 1.3*
Bajocian 170.3 ± 1.4*
Aalenian 174.1 ± 1.0*
Early Toarcian 182.7 ± 0.7*
Pliensbachian 190.8 ± 1.0*
Sinemurian 199.3 ± 0.3*
Hettangian 201.3 ± 0.2*
Triassic Late Rhaetian Archosaurs dominant on land as pseudosuchians and in the air as pterosaurs. Dinosaurs also arise from archosaurs. Ichthyosaurs and nothosaurs dominate large marine fauna. Cynodonts become smaller and nocturnal, eventually becoming the first true mammals. Dicroidiumflora common on land. Many large aquatic temnospondyl amphibians while modern ones may have emerged from them in this period. Ceratitic ammonoids extremely common. Modern corals and teleost fish appear, as do many modern insect clades. Andean Orogeny in South America. Cimmerian Orogeny in Asia. Rangitata Orogeny begins in New Zealand. Hunter-Bowen Orogeny in Northern Australia, Queensland and New South Wales ends, (c. 260–225 Ma) ~208.5
Norian ~227
Carnian ~237*
Middle Ladinian ~242*
Anisian 247.2
Early Olenekian 251.2
Induan 251.902 ± 0.06*
Paleozoic Permian Lopingian Changhsingian Landmasses unite into supercontinent Pangaea, creating the Appalachians. End of Permo-Carboniferous glaciation. Synapsids (including pelycosaurs and therapsids) become dominant, while parareptiles and temnospondyl amphibians remain common. In the mid-Permian, coal-age flora are replaced by cone-bearing gymnosperms (the first true seed plants) and by the first true mosses. Beetles and flies evolve. Marine life flourishes in warm shallow reefs; productid and spiriferid brachiopods, bivalves, forams, and ammonoids all abundant. Cynodonts evolve from larger therapsids. Permian-Triassic extinction event occurs 251 Ma: 95% of life on Earth becomes extinct, including all trilobites, graptolites, and blastoids. Ouachita and Innuitian orogenies in North America. Uralian orogeny in Europe/Asia tapers off. Altaid orogeny in Asia. Hunter-Bowen Orogeny on Australian continent begins (c. 260–225 Ma), forming the MacDonnell Ranges. 254.14 ± 0.07*
Wuchiapingian 259.1 ± 0.4*
Guadalupian Capitanian 265.1 ± 0.4*
Wordian 268.8 ± 0.5*
Roadian 272.95 ± 0.5*
Cisuralian Kungurian 283.5 ± 0.6
Artinskian 290.1 ± 0.26
Sakmarian 295 ± 0.18
Asselian 298.9 ± 0.15*
Carbon-
iferous[g] 		Pennsylvanian Gzhelian Winged insects radiate suddenly; some (esp. Protodonata and Palaeodictyoptera) of them as well some millipedes and scorpions become very large. First coal forests (scale trees, ferns, club trees, giant horsetails, Cordaites, etc.). Highest-ever atmospheric oxygen levels. Goniatites, brachiopods, bryozoa, bivalves, and corals plentiful in the seas and oceans. Testate forams proliferate. Uralian orogeny in Europe and Asia. Variscan orogeny occurs towards middle and late Mississippian Periods. Amphibians became quite plentiful while the first amniotes also evolved, replacing the amphibians while the seed plants replaced pteridophytes after the Carboniferous Rainforest Collapse. Rhizodonts remained common. 303.7 ± 0.1
Kasimovian 307 ± 0.1
Moscovian 315.2 ± 0.2
Bashkirian 323.2 ± 0.4*
Mississippian Serpukhovian Large primitive trees and amphibious sea-scorpions live amid coal-forming coastal swamps. First five-digited tetrapods. In the oceans, early sharks are common and quite diverse; echinoderms (especially crinoids and blastoids) abundant. Corals, bryozoa, goniatites and brachiopods (Productida, Spiriferida, etc.) very common, but trilobites and nautiloids decline. Glaciation in East Gondwana. Tuhua Orogeny in New Zealand tapers off. Some lobe finned fish called rhizodonts become abundant and dominant in freshwaters. 330.9 ± 0.2
Viséan 346.7 ± 0.4*
Tournaisian 358.9 ± 0.4*
Devonian Late Famennian First lycopods, ferns and seed-bearing plants (progymnosperms and, later, seed ferns), first trees (the progymnosperm Archaeopteris), and first (winged) insects. Strophomenid and brachiopods, rugose and tabulate corals, and crinoids are all abundant in the oceans. Goniatite ammonoids are plentiful, while squid-like coleoids arise. Trilobites and armoured agnaths decline, while jawed fishes (placoderms, lobe-finned and ray-finned fish, and early sharks) become plentiful. Some lobe finned fish transform into digited fishapods, slowly becoming amphibious. "Old Red Continent" of Euramerica. Beginning of Acadian Orogeny for Anti-Atlas Mountains of North Africa, and Appalachian Mountains of North America, also the Antler, Variscan, and Tuhua Orogeny in New Zealand. 372.2 ± 1.6*
Frasnian 382.7 ± 1.6*
Middle Givetian 387.7 ± 0.8*
Eifelian 393.3 ± 1.2*
Early Emsian 407.6 ± 2.6*
Pragian 410.8 ± 2.8*
Lochkovian 419.2 ± 3.2*
Silurian Pridoli First vascular plants and fully terrestrialized arthropods: myriapods, hexapods, and arachnids. First jawed fishes, as well as many ostracoderms, populate the seas. Sea-scorpions reach large size. Tabulate and rugose corals, brachiopods (Pentamerida, Rhynchonellida, etc.), and crinoids all abundant. Trilobites and mollusks diverse; graptolites not as varied. Beginning of Caledonian Orogeny for hills in England, Ireland, Wales, Scotland, and the Scandinavian Mountains. Also continued into Devonian period as the Acadian Orogeny, above. Taconic Orogeny tapers off. Lachlan Orogeny on Australian continent tapers 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 Late Hirnantian Invertebrates diversify into many new types (e.g., long straight-shelled cephalopods). Early corals, articulate brachiopods (Orthida, Strophomenida, etc.), bivalves, nautiloids, trilobites, ostracods, bryozoa, many types of echinoderms (crinoids, cystoids, starfish, etc.), branched graptolites, and other taxa all common. First ostracoderm fish appear. First uncontroversial terrestrial fungi and fully terrestrialized plants. Ice age at the end of this period. 445.2 ± 1.4*
Katian 453 ± 0.7*
Sandbian 458.4 ± 0.9*
Middle Darriwilian 467.3 ± 1.1*
Dapingian 470 ± 1.4*
Early Floian
(formerly Arenig) 		477.7 ± 1.4*
Tremadocian 485.4 ± 1.9*
Cambrian Furongian Stage 10 Major diversification of life in the Cambrian Explosion. Numerous fossils; most modern animal phyla appear. Reef-building Archaeocyatha abundant; then vanish. Trilobites, priapulid worms, sponges, inarticulate brachiopods (unhinged lampshells), and numerous other animals. Anomalocarids are giant predators, while many Ediacaran fauna die out. Prokaryotes, protists (e.g., forams), fungi and algae continue to present day. First chordates (later also first vertebrates) appear, along with a number of extinct, problematic phyla. Gondwana emerges. Petermann Orogeny on the Australian continent tapers off (550–535 Ma). Ross Orogeny in Antarctica. Delamerian Orogeny (c. 514–490 Ma) and Lachlan Orogeny (c. 540–440 Ma) on Australian continent. Atmospheric CO2 content roughly 15 times present-day (Holocene) levels (6000 ppmv compared to today's 400 ppmv)[45][f] Life starting to expand on land, in the form of green algae and arthropods. ~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 ~541 ± 1.0*
Precambrian[h] Proterozoic[i] Neoproterozoic[i] Ediacaran Good fossils of primitive animals. Ediacaran biota flourish worldwide in seas. Simple trace fossils of possible worm-like Trichophycus, etc. First vendozoans (unknown affinity among animals), cnidarians and bilaterians. Enigmatic forms include many soft-jellied creatures shaped like bags, disks, or quilts (like Dickinsonia). Taconic Orogeny in North America. Aravalli Range orogeny in Indian subcontinent. Beginning of Petermann Orogeny on Australian continent. Beardmore Orogeny in Antarctica, 633–620 Ma. ~635*
Cryogenian Possible "Snowball Earth" period. Fossils still rare. Rodinia landmass begins to break up. Late Ruker / Nimrod Orogeny in Antarctica tapers off. First uncontroversial animal fossils. First hypothetical terrestrial fungi and streptophyta. ~720[j]
Tonian Rodinia supercontinent persists. Sveconorwegian orogeny ends. Trace fossils of simple multi-celled eukaryotes. First radiation of dinoflagellate-like acritarchs. Grenville Orogeny tapers off in North America. Pan-African orogeny in Africa. Lake Ruker / Nimrod Orogeny in Antarctica, 1,000 ± 150 Ma. Edmundian Orogeny (c. 920 – 850 Ma), Gascoyne Complex, Western Australia. Deposition of Adelaide Superbasin and Centralian Superbasin begins on Australian continent. First hypothetical animals. 1000[j]
Mesoproterozoic[i] Stenian Narrow highly metamorphic belts due to orogeny as Rodinia forms. Sveconorwegian orogeny starts. Late Ruker / Nimrod Orogeny in Antarctica possibly begins. Musgrave Orogeny (c. 1,080 Ma), Musgrave Block, Central Australia. 1200[j]
Ectasian Platform covers continue to expand. Green algae colonies in the seas. Grenville Orogeny in North America. 1400[j]
Calymmian Platform covers expand. Barramundi Orogeny, McArthur Basin, Northern Australia, and Isan Orogeny, c. 1,600 Ma, Mount Isa Block, Queensland 1600[j]
Paleoproterozoic[i] Statherian First complex single-celled life: protists with nuclei, Francevillian biota. Columbia is the primordial supercontinent. Kimban Orogeny in Australian continent ends. Yapungku Orogeny on Yilgarn craton, in Western Australia. Mangaroon Orogeny, 1,680–1,620 Ma, on the Gascoyne Complex in Western Australia. Kararan Orogeny (1,650 Ma), Gawler Craton, South Australia. 1800[j]
Orosirian The atmosphere becomes oxygenic. Vredefort and Sudbury Basin asteroid impacts. Much orogeny. Penokean and Trans-Hudsonian Orogenies in North America. Early Ruker Orogeny in Antarctica, 2,000–1,700 Ma. Glenburgh Orogeny, Glenburgh Terrane, Australian continent c. 2,005–1,920 Ma. Kimban Orogeny, Gawler craton in Australian continent begins. 2050[j]
Rhyacian Bushveld Igneous Complex forms. Huronian glaciation. 2300[j]
Siderian Oxygen catastrophe: banded iron formations forms. Sleaford Orogeny on Australian continent, Gawler Craton 2,440–2,420 Ma. 2500[j]
Archean[i] Neoarchean[i] Stabilization of most modern cratons; possible mantle overturn event. Insell Orogeny, 2,650 ± 150 Ma. Abitibi greenstone belt in present-day Ontario and Quebec begins to form, stabilizes by 2,600 Ma. 2800[j]
Mesoarchean[i] First stromatolites (probably colonial cyanobacteria). Oldest macrofossils. Humboldt Orogeny in Antarctica. Blake River Megacaldera Complex begins to form in present-day Ontario and Quebec, ends by roughly 2,696 Ma. 3200[j]
Paleoarchean[i] First known oxygen-producing bacteria. Oldest definitive microfossils. Oldest cratons on Earth (such as the Canadian Shield and the Pilbara Craton) may have formed during this period.[k] Rayner Orogeny in Antarctica. 3600[j]
Eoarchean[i] Simple single-celled life (probably bacteria and archaea). Oldest probable microfossils. The first life forms and self-replicating RNA molecules evolve around 4,000 Ma, after the Late Heavy Bombardment ends on Earth. Napier Orogeny in Antarctica, 4,000 ± 200 Ma. ~4000
Hadean[i][l] Early Imbrian (Neohadean) (unofficial)[i][m] Indirect photosynthetic evidence (e.g., kerogen) of primordial life. This era overlaps the beginning of the Late Heavy Bombardment of the Inner Solar System, produced possibly by the planetary migration of Neptune into the Kuiper belt as a result of orbital resonances between Jupiter and Saturn. Oldest known rock (4,031 to 3,580 Ma).[49] 4130[50]
Nectarian (Mesohadean) (unofficial)[i][m] Possible first appearance of plate tectonics. This unit gets its name from the lunar geologic timescale when the Nectaris Basin and other greater lunar basins form by big impact events. Earliest evidence for life based on unusually high amounts of light isotopes of carbon, a common sign of life. 4280[50]
Basin Groups (Paleohadean) (unofficial)[i][m] End of the Early Bombardment Phase. Oldest known mineral (Zircon, 4,404 ± 8 Ma).[51] Asteroids and comets bring water to Earth.[52] 4533[50]
Cryptic (Eohadean) (unofficial)[i][m] Formation of Moon (4,533 to 4,527 Ma), probably from giant impact, since the end of this era. Formation of Earth (4,570 to 4,567.17 Ma), Early Bombardment Phase begins. Formation of Sun (4,680 to 4,630 Ma) . 4600

Proposed Precambrian timeline[]

The ICS's Geologic Time Scale 2012 book which includes the new approved time scale also displays a proposal to substantially revise the Precambrian time scale to reflect important events such as the formation of the Earth or the Great Oxidation Event, among others, while at the same time maintaining most of the previous chronostratigraphic nomenclature for the pertinent time span.[53] (See also Period (geology)#Structure.)

  • Hadean Eon – 4568–4030 Ma
    • Chaotian Era – 4568–4404 Ma – the name alluding both to the mythological Chaos and the chaotic phase of planet formation[53][50][54]
    • Jack Hillsian or Zirconian Era – 4404–4030 Ma – both names allude to the Jack Hills Greenstone Belt which provided the oldest mineral grains on Earth, zircons[53][50]
  • Archean Eon – 4031–2420 Ma
    • Paleoarchean Era – 4031–3490 Ma
      • Acastan Period – 4031–3810 Ma – named after the Acasta Gneiss[53][50]
      • Isuan Period – 3810–3490 Ma – named after the Isua Greenstone Belt[53]
    • Mesoarchean Era – 3490–2780 Ma
      • Vaalbaran Period – 3490–3020 Ma – based on the names of the Kapvaal (Southern Africa) and Pilbara (Western Australia) cratons[53]
      • Pongolan Period – 3020–2780 Ma – named after the Pongola Supergroup[53]
    • Neoarchean Era – 2780–2420 Ma
      • Methanian Period – 2780–2630 Ma – named for the inferred predominance of methanotrophic prokaryotes[53]
      • Siderian Period – 2630–2420 Ma – named for the voluminous banded iron formations formed within its duration[53]
  • Proterozoic Eon – 2420–541 Ma
    • Paleoproterozoic Era – 2420–1780 Ma
      • Oxygenian Period – 2420–2250 Ma – named for displaying the first evidence for a global oxidizing atmosphere[53]
      • Jatulian or Eukaryian Period – 2250–2060 Ma – names are respectively for the Lomagundi–Jatuli δ13C isotopic excursion event spanning its duration, and for the (proposed)[55][56] first fossil appearance of eukaryotes[53]
      • Columbian Period – 2060–1780 Ma – named after the supercontinent Columbia[53]
    • Mesoproterozoic Era – 1780–850 Ma
      • Rodinian Period – 1780–850 Ma – named after the supercontinent Rodinia, stable environment[53]
    • Neoproterozoic Era – 850–541 Ma
      • Cryogenian Period – 850–630 Ma – named for the occurrence of several glaciations[53]
      • Ediacaran Period – 630–541 Ma

Shown to scale:

AcastanIsuanVaalbaranPongolanMethanianSiderianOxygenianEukaryianColumbianRodinianCryogenianEdiacaranChaotianPaleoarcheanMesoarcheanNeoarcheanPaleoproterozoicMesoproterozoicNeoproterozoicHadeanArcheanProterozoicPrecambrian

Compare with the current official timeline, not shown to scale:

SiderianRhyacianOrosirianStatherianCalymmianEctasianStenianTonianCryogenianEdiacaranEoarcheanPaleoarcheanMesoarcheanNeoarcheanPaleoproterozoicMesoproterozoicNeoproterozoicHadeanArcheanProterozoicPrecambrian

See also[]

Notes[]

  1. ^ Not enough is known about extra-solar planets for worthwhile speculation.
  2. ^ Paleontologists often refer to faunal stages rather than geologic (geological) periods. The stage nomenclature is quite complex. For a time-ordered list of faunal stages, see.[40]
  3. ^ a b Dates are slightly uncertain with differences of a few percent between various sources being common. This is largely due to uncertainties in radiometric dating and the problem that deposits suitable for radiometric dating seldom occur exactly at the places in the geologic column where they would be most useful. The dates and errors quoted above are according to the International Commission on Stratigraphy 2015 time scale except the Hadean eon. Where errors are not quoted, errors are less than the precision of the age given.

    * indicates boundaries where a Global Boundary Stratotype Section and Point has been internationally agreed upon.
  4. ^ References to the "Post-Cambrian Supereon" are not universally accepted, and therefore must be considered unofficial.
  5. ^ Historically, the Cenozoic has been divided up into the Quaternary and Tertiary sub-eras, as well as the Neogene and Paleogene periods. The 2009 version of the ICS time chart[41] recognizes a slightly extended Quaternary as well as the Paleogene and a truncated Neogene, the Tertiary having been demoted to informal status.
  6. ^ a b c d For more information on this, see Atmosphere of Earth#Evolution of Earth's atmosphere, Carbon dioxide in the Earth's atmosphere, and climate change. Specific graphs of reconstructed CO2 levels over the past ~550, 65, and 5 million years can be seen at File:Phanerozoic Carbon Dioxide.png, File:65 Myr Climate Change.png, File:Five Myr Climate Change.png, respectively.
  7. ^ In North America, the Carboniferous is subdivided into Mississippian and Pennsylvanian Periods.
  8. ^ The Precambrian is also known as Cryptozoic.
  9. ^ a b c d e f g h i j k l m n The Proterozoic, Archean and Hadean are often collectively referred to as the Precambrian or, sometimes, the Cryptozoic.
  10. ^ a b c d e f g h i j k l Defined by absolute age (Global Standard Stratigraphic Age).
  11. ^ The age of the oldest measurable craton, or continental crust, is dated to 3,600–3,800 Ma.
  12. ^ Though commonly used, the Hadean is not a formal eon[48] and no lower bound for the Archean and Eoarchean have been agreed upon. The Hadean has also sometimes been called the Priscoan or the Azoic. Sometimes, the Hadean can be found to be subdivided according to the lunar geologic timescale. These eras include the Cryptic and Basin Groups (which are subdivisions of the Pre-Nectarian era), Nectarian, and Early Imbrian units.
  13. ^ a b c d These unit names were taken from the lunar geologic timescale and refer to geologic events that did not occur on Earth. Their use for Earth geology is unofficial. Note that their start times do not dovetail perfectly with the later, terrestrially defined boundaries.

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Further reading[]

External links[]

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