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).
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, which are in turn divided into periods, 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, millions of
|Archean||Neoarchean||Not officially divided into periods||300|
|Hadean||Not officially divided into eras||Not officially divided into periods||From formation of Earth to
|Segments of rock (strata) in chronostratigraphy||Time spans in geochronology||Notes to|
|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.
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. The adjectives are capitalized when the subdivision is formally recognized, and lower case when not; thus "early Miocene" but "Early Jurassic."
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. 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.
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, the Archean has been divided into four eras and the Proterozoic has been divided into three eras.
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. 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.
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.
The set of rocks (sedimentary, igneous or metamorphic) formed during a period belong to a chronostratigraphic unit called a system. For example, the "Jurassic System" of rocks was formed during the "Jurassic Period" (between 201 and 145 million years ago).
Evidence from radiometric dating indicates that Earth is about 4.54 billion years old. 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.
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]
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.
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. 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). The Chinese naturalist Shen Kuo (1031–1095) also recognized the concept of "deep time".
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:
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 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".: 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.
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.
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.: 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 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.
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. 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. 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.
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.
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. A UML model for how the timescale is structured, relating it to the GSSP, is also available.
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. Cases like this in China, Russia and even New Zealand with other geological eras has slowed the uniform organization of the stratigraphic record.
Popular culture and a growing number of scientists use the term "Anthropocene" informally to label the current epoch in which we are living. 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.
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.
The ICS has not officially approved the term as of September 2015[update]. The Anthropocene Working Group met in Oslo in April 2016 to consolidate evidence supporting the argument for the Anthropocene as a true geologic epoch. Evidence was evaluated and the group voted to recommend "Anthropocene" as the new geological age in August 2016. 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.
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), with the epoch names altered to the early/late format from lower/upper as recommended by the ICS when dealing with chronostratigraphy.
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 and at a SPARQL end-point.
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).
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 and Holocene extinction 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. Pleistocene megafauna extinction.||0.129|
|Chibanian||Mid-Pleistocene Transition occurs, 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 as the cold slowly intensifies towards the Pleistocene. Australopithecus common in East Africa.||3.6*|
|Zanclean||Zanclean flooding of the Mediterranean Basin. First equines and elephantines. Cooling climate continues from the Miocene. Ardipithecus in Africa.||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. Choristoderes, the last creodonts and non-marsupial metatherians go extinct. After separating from gorilla ancestors, chimpanzee and human ancestors gradually separate; Sahelanthropus and Orrorin in Africa.||7.246*|
|Serravallian||Middle Miocene climate optimum temporarily provides a warm climate. Extinctions in middle Miocene disruption, decreasing shark diversity. Ancestor of great apes.||13.82*|
|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.[f] Modern bird and mammal families become recognizable. First neocetes (modern, fully aquatic whales) while primitive ones vanish. Grasses become ubiquitous. Ancestor of apes, including humans.||20.44|
|Paleogene||Oligocene||Chattian||Grande Coupure extinction. Start of widespread Antarctic glaciation. Rapid evolution and diversification of fauna, especially mammals (e.g. first macropods and seals). Major evolution and dispersal of modern types of flowering plants. Cimolestans, miacoids and condylarths go extinct.||28.1|
|Eocene||Priabonian||Moderate, cooling climate. Archaic mammals (e.g. Creodonts, Miacoids, "Condylarths" etc.) flourish and continue to develop during the epoch. Appearance of several "modern" mammal families. Primitive whales and sea cows diversify after returning to water. Birds continue to diversify. First kelp, diprotodonts and simians. The multituberculates and leptictidans go extinct by the end of the epoch. 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|
|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.[f] Indian subcontinent collides with Eurasia and starts Himalayan Orogeny while Eurasia completely separates from North America, creating the North Atlantic Ocean. First passerines, ruminants, bats and true primates.||56*|
|Paleocene||Thanetian||Starts with Chicxulub impact and the K-Pg extinction event, wiping out all non-avian dinosaurs and pterosaurs, most marine reptiles, many other vertebrates (e.g. many Laurasian metatherians), most cephalopods (only Nautilidae and Coleoidea survived) and many other invertebrates. Climate tropical. Mammals and birds (avians) diversify rapidly into a number of lineages following the extinction event (while the marine revolution stops). Multituberculates and the first rodents widespread. First large birds (e.g. ratites and terror birds) and mammals (up to bear or small hippo size). Alpine orogeny in Europe and Asia begins. First proboscideans and plesiadapiformes (stem primates) appear. Some marsupials migrate to Australia.||59.2*|
|Mesozoic||Cretaceous||Late||Maastrichtian||Flowering plants proliferate, along with new types of insects. More modern teleost fish begin to appear. Ammonoids, belemnites, rudist bivalves, sea urchins 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 probably cause the last temnospondyls to die out; and mosasaurs and modern types of sharks appear in the sea. The revolution started by marine reptiles and sharks reaches its peak, though ichthyosaurs vanish few million years after being heavily reduced at the Bonarelli Event. Toothed and toothless avian birds coexist with pterosaurs. Modern monotremes, metatherian (including marsupials, who migrate to South America) and eutherian (including placentals, leptictidans and cimolestans) mammals appear while the last non-mammalian cynodonts die out. First terrestrial crabs. Break up of Gondwana. Beginning of Laramide and Sevier Orogenies of the Rocky Mountains. Atmospheric CO2 close to present-day levels. Acritarchs disappear. Climate intially warm, but later it cools.||72.1 ± 0.2*|
|Campanian||83.6 ± 0.2|
|Santonian||86.3 ± 0.5*|
|Coniacian||89.8 ± 0.3|
|Jurassic||Late||Tithonian||Climate becomes humid again. Gymnosperms (especially conifers, cycads and cycadeoids) and ferns common. Dinosaurs, including sauropods, carnosaurs, stegosaurs and coelurosaurs, become the dominant land vertebrates. Mammals diversify into shuotheriids, australosphenidans, eutriconodonts, multituberculates, symmetrodonts, dryolestids and boreosphenidans but mostly remain small. First birds, lizards, snakes and turtles. First brown algae, rays, shrimps, crabs and lobsters. Parvipelvian ichthyosaurs and plesiosaurs diverse. Rhynchocephalians throughout the world. Bivalves, Ammonoids and belemnites abundant. Sea urchins very common, along with crinoids, starfish, sponges, and terebratulid and rhynchonellid brachiopods. Breakup of Pangaea into Gondwana and Laurasia: beginning of the opening of the North Atlantic Ocean. 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[f]). Crocodylomorphs (last pseudosuchians) seek out an aquatic lifestyle. Mesozoic marine revolution continues from late Triassic. Tentaculitans disappear.||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 bipedal archosaurs. Ichthyosaurs and nothosaurs (a group of sauropterygians) dominate large marine fauna. Cynodonts become smaller and nocturnal, eventually becoming the first true mammals, while other remaining synapsids die out. Rhynchosaurs (archosaur relatives) also common. Dicroidium flora common on land. Many large aquatic temnospondyl amphibians. Ceratitidan ammonoids extremely common. Modern corals and teleost fish appear, as do many modern insect orders and suborders. First starfish. 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). Carnian pluvial event occurs around 234-232 Ma, allowing the first dinosaurs and lepidosaurs (including rhynchocephalians) to radiate. Triassic-Jurassic extinction event occurs 201 Ma, wiping out all conodonts and the last parareptiles, many marine reptiles (e.g. all sauropterygians except plesiosaurs and all ichthyosaurs except parvipelvians) all crocopodans except crocodylomorphs, pterosaurs, and dinosaurs, and many ammonoids (including the whole Ceratitida), bivalves, brachiopods, corals and sponges. First diatoms.||~208.5|
|Induan||251.902 ± 0.06*|
|Paleozoic||Permian||Lopingian||Changhsingian||Landmasses unite into supercontinent Pangaea, creating the Urals, Ouachitas and Appalachians, among other mountain ranges. End of Permo-Carboniferous glaciation. Hot and dry climate. Synapsids (pelycosaurs and therapsids) become widespread and dominant, while parareptiles and temnospondyl amphibians remain common, with the latter probably giving rise to modern amphibians in this period. In the mid-Permian, coal-age flora are replaced by cone-bearing gymnosperms and by the first true mosses. Beetles and flies evolve. The very large arthropods and non-tetrapod tetrapodomorphs go extinct. Marine life flourishes in warm shallow reefs; productid and spiriferid brachiopods, bivalves, forams, ammonoids (including goniatites), and orthoceridans all abundant. Crown reptiles arise from earlier diapsids, and split into ancestors of lepidosaurs, kuehneosaurids, choristoderes, archosaurs, testudinatans, ichthyosaurs, thalattosaurs, and sauropterygians. Cynodonts evolve from larger therapsids. Olson's Extinction (273 Ma), End-Capitanian extinction (260 Ma), and Permian-Triassic extinction event (252 Ma) occur one after another: more than 80% of life on Earth becomes extinct in the lattermost, including most retarian plankton, corals (Tabulata and Rugosa die out fully), brachiopods, bryozoans, gastropods, ammonoids (the goniatites die off fully), insects, parareptiles, synapsids, amphibians, and crinoids (only articulates survived), and all eurypterids, trilobites, graptolites, hyoliths, edrioasteroid crinozoans, blastoids and acanthodians. 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*|
|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. Ice Age continues to the Early Permian. Goniatites, brachiopods, bryozoa, bivalves, and corals plentiful in the seas and oceans. First woodlice. Testate forams proliferate. Euramerica collides with Gondwana and Siberia-Kazakhstania, the latter of which forms Laurasia and the Uralian orogeny. Variscan orogeny continues (these collisions created orogenies, and ultimately Pangaea). Amphibians spread in Euramerica, with some becoming the first amniotes. Carboniferous Rainforest Collapse occurs, initiating a dry climate which favors seed plants over pteridophytes and amniotes over amphibians. Amniotes diversify rapidly into synapsids, parareptiles, cotylosaurs, protorothyridids and diapsids. Rhizodonts remained common before they died out by the end of the period. First sharks.||303.7 ± 0.1|
|Kasimovian||307 ± 0.1|
|Moscovian||315.2 ± 0.2|
|Bashkirian||323.2 ± 0.4*|
|Mississippian||Serpukhovian||Large lycopodian primitive trees flourish and amphibious eurypterids live amid coal-forming coastal swamps, radiating significantly one last time. First holometabolous, paraneopteran, polyneopteran, odonatopteran and ephemeropteran insects and first barnacles. First five-digited tetrapods (amphibians) and land snails. In the oceans, bony and cartilaginous fishes are dominant and diverse; echinoderms (especially crinoids and blastoids) abundant. Corals, bryozoans, orthoceridans, goniatites and brachiopods (Productida, Spiriferida, etc.) recover and become very common again, but trilobites and nautiloids decline. Glaciation in East Gondwana continues from Late Devonian. Tuhua Orogeny in New Zealand tapers off. Some lobe finned fish called rhizodonts become abundant and dominant in freshwaters. Siberia collides with a different small continent, Kazakhstania.||330.9 ± 0.2|
|Viséan||346.7 ± 0.4*|
|Tournaisian||358.9 ± 0.4*|
|Devonian||Late||Famennian||First lycopods, ferns, seed plants (seed ferns, from earlier progymnosperms), first trees (the progymnosperm Archaeopteris), and first winged insects (palaeoptera and neoptera). Strophomenid and atrypid brachiopods, rugose and tabulate corals, and crinoids are all abundant in the oceans. First fully coiled cephalopods (Ammonoidea and Nautilida, independently) with the former group very abundant (especially goniatites). Trilobites and ostracoderms decline, while jawed fishes (placoderms, lobe-finned and ray-finned bony fish, and acanthodians and early cartilaginous fish) proliferate. Some lobe finned fish transform into digited fishapods, slowly becoming amphibious. The last non-trilobite artiopods die off. First decapods (like prawns) and isopods. Pressure from jawed fishes cause eurypterids to decline and some cephalopods to lose their shells while anomalocarids vanish. "Old Red Continent" of Euramerica persists after forming in the Caledonian orogeny. Beginning of Acadian Orogeny for Anti-Atlas Mountains of North Africa, and Appalachian Mountains of North America, also the Antler, Variscan, and Tuhua orogenies in New Zealand. A series of extinction events, including the massive Kellwasser and Hangenberg ones, wipe out many acritarchs, corals, sponges, molluscs, trilobites, eurypterids, graptolites, brachiopods, crinozoans (e.g. all cystoids), 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*|
|Early||Emsian||407.6 ± 2.6*|
|Pragian||410.8 ± 2.8*|
|Lochkovian||419.2 ± 3.2*|
|Silurian||Pridoli||Ozone layer thickens. First vascular plants and fully terrestrialized arthropods: myriapods, hexapods (including insects), and arachnids. Eurypterids diversify rapidly, becoming widespread and dominant. Cephalopods continue to flourish. True jawed fishes, along with ostracoderms, also roam the seas. Tabulate and rugose corals, brachiopods (Pentamerida, Rhynchonellida, etc.), cystoids and crinoids all abundant. Trilobites and molluscs diverse; graptolites not as varied. Three minor extinction events. Some echinoderms go extinct. Beginning of Caledonian Orogeny (collision between Laurentia, Baltica and one of the formerly small Gondwanan terranes) for hills in England, Ireland, Wales, Scotland, and the Scandinavian Mountains. Also continued into Devonian period as the Acadian Orogeny, above (thus Euramerica forms). Taconic Orogeny tapers off. Icehouse period ends late in this period after starting in Late Ordovician. 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||The Great Ordovician Biodiversification Event occurs as plankton increase in number: invertebrates diversify into many new types (especially brachiopods and molluscs; e.g. long straight-shelled cephalopods like the long lasting and diverse Orthocerida). Early corals, articulate brachiopods (Orthida, Strophomenida, etc.), bivalves, cephalopods (nautiloids), trilobites, ostracods, bryozoans, many types of echinoderms (blastoids, cystoids, crinoids, sea urchins, sea cucumbers, and star-like forms, etc.), branched graptolites, and other taxa all common. Acritarchs still persist and common. Cephalopods become dominant and common, with some trending toward a coiled shell. Anomalocarids decline. Mysterious tentaculitans appear. First eurypterids and ostracoderm fish appear, the latter probably giving rise to the jawed fish at the end of the period. First uncontroversial terrestrial fungi and fully terrestrialized plants. Ice age at the end of this period, as well as a series of mass extinction events, killing off some cephalopods and many brachiopods, bryozoans, echinoderms, graptolites, trilobites, bivalves, corals and conodonts.||445.2 ± 1.4*|
|Katian||453 ± 0.7*|
|Sandbian||458.4 ± 0.9*|
|Middle||Darriwilian||467.3 ± 1.1*|
|Dapingian||470 ± 1.4*|
|477.7 ± 1.4*|
|Tremadocian||485.4 ± 1.9*|
|Cambrian||Furongian||Stage 10||Major diversification of (fossils mainly show bilaterian) life in the Cambrian Explosion as oxygen levels increase. Numerous fossils; most modern animal phyla (including arthropods, molluscs, annelids, echinoderms, hemichordates and chordates) appear. Reef-building archaeocyathan sponges initially abundant, then vanish. Stromatolites replace them, but quickly fall prey to the Agronomic revolution, when some animals started burrowing through the microbial mats (affecting some other animals as well). First artiopods (including trilobites), priapulid worms, inarticulate brachiopods (unhinged lampshells), hyoliths, bryozoans, graptolites, pentaradial echinoderms (e.g. blastozoans, crinozoans and eleutherozoans), and numerous other animals. Anomalocarids are dominant and giant predators, while many Ediacaran fauna die out. Crustaceans and molluscs diversify rapidly. Prokaryotes, protists (e.g., forams), algae and fungi continue to present day. First vertebrates from earlier chordates. 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. Some small terranes split off from Gondwana. Atmospheric CO2 content roughly 15 times present-day (Holocene) levels (6000 ppmv compared to today's 400 ppmv)[f] Life starting to expand on land, in the form of multi-celled green algae and arthropods. 3 extinction events occur 517, 502 & 488 Ma, the first and last of which wipe out many of the anomalocarids, artiopods, hyoliths, brachiopods, molluscs, and conodonts (early jawless vertebrates).||~489.5|
|Series 2||Stage 4||~514|
|Fortunian||~541 ± 1.0*|
|Precambrian[h]||Proterozoic[i]||Neoproterozoic[i]||Ediacaran||Good fossils of primitive animals. Ediacaran biota flourish worldwide in seas, possibly appearing after an explosion, possibly caused by a large-scale oxidation event. First vendozoans (unknown affinity among animals), cnidarians and bilaterians. Enigmatic vendozoans include many soft-jellied creatures shaped like bags, disks, or quilts (like Dickinsonia). Simple trace fossils of possible worm-like Trichophycus, etc.Taconic Orogeny in North America. Aravalli Range orogeny in Indian subcontinent. Beginning of Pan-African Orogeny, leading to the formation of the short-lived Ediacaran supercontinent Pannotia, which by the end of the period breaks up into Laurentia, Baltica, Siberia and Gondwana. Petermann Orogeny forms on Australian continent. Beardmore Orogeny in Antarctica, 633–620 Ma. Ozone layer forms. An increase in oceanic mineral levels.||~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. Grenville Orogeny tapers 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 of Adelaide Superbasin and Centralian Superbasin begins on Australian continent. First hypothetical animals (from holozoans) and terrestrial algal mats. Many endosymbiotic events concerning red and green algae occur, transferring plastids to ochrophyta (e.g. diatoms, brown algae), dinoflagellates, cryptophyta, haptophyta, and euglenids (the events may have begun in the Mesoproterozoic) while the first retarians (e.g. forams) also appear: eukaryotes diversify rapidly, including algal, eukaryovoric and biomineralized forms. Trace fossils of simple multi-celled eukaryotes.||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. Stromatolites decline as algae proliferate.||1200[j]|
|Ectasian||Platform covers continue to expand. Algal colonies in the seas. Grenville Orogeny in North America. Columbia breaks up.||1400[j]|
|Calymmian||Platform covers expand. Barramundi Orogeny, McArthur Basin, Northern Australia, and Isan Orogeny, c. 1,600 Ma, Mount Isa Block, Queensland. First archaeplastidans (the first eukaryotes with plastids from cyanobacteria; e.g. red and green algae) and opisthokonts (giving rise to the first fungi and holozoans). Acritarchs (remains of marine algae possibly) start appearing in the fossil record.||1600[j]|
|Paleoproterozoic[i]||Statherian||First uncontroversial eukaryotes: protists with nuclei and endomembrane system. Columbia forms as the second earliest 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. Oxygen levels drop again.||1800[j]|
|Orosirian||The atmosphere becomes much more oxygenic while more cyanobacterial stromatolites appear. 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. First hypothetical eukaryotes. Multicellular Francevillian biota. Kenorland disassembles.||2300[j]|
|Siderian||Great Oxidation Event (due to cyanobacteria) increases oxygen. 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. First supercontinent, Kenorland, and first terrestrial prokaryotes.||2800[j]|
|Mesoarchean[i]||First stromatolites (probably colonial phototrophic bacteria, like 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]||Prokaryotic archaea (e.g. methanogens) and bacteria (e.g. cyanobacteria) diversify rapidly, along with early viruses. First known phototrophic bacteria. Oldest definitive microfossils. First microbial mats. 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]||First uncontroversial living organisms: at first protocells with RNA-based genes around 4000 Ma, after which true cells (prokaryotes) evolve along with proteins and DNA-based genes around 3800 Ma. The end of the Late Heavy Bombardment. Napier Orogeny in Antarctica, 4,000 ± 200 Ma.||~4000|
|Hadean[i][l]||Early Imbrian (Neohadean) (unofficial)[i][m]||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).||4130|
|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. First controversial life forms.||4280|
|Basin Groups (Paleohadean) (unofficial)[i][m]||End of the Early Bombardment Phase. Oldest known mineral (Zircon, 4,404 ± 8 Ma). Asteroids and comets bring water to Earth.||4533|
|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|
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. (See also Period (geology)#Structure.)
Shown to scale:
Compare with the current official timeline, not shown to scale:
((cite web)): CS1 maint: archived copy as title (link)