The geologic time scale (GTS) is a system of chronological dating that relates geological strata (stratigraphy) to time. It is used by geologists, paleontologists, and other Earth scientists to describe the timing and relationships of events that have occurred during Earth's history. The table of geologic time spans, presented here, agree with the nomenclature, dates and standard color codes set forth by the International Commission on Stratigraphy (ICS).
The primary defined divisions of time are eons, in sequence the Hadean, the Archean, the Proterozoic and the Phanerozoic. The first three of these can be referred to collectively as the Precambrian supereon. Eons are divided into eras, which are in turn divided into periods, epochs and ages.
The following four 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, and the most recent period is expanded in the fourth timeline.
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."
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 which took 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 and 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 look different 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 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 preserve their history in a comparable manner. 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 debated.[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 geologist 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 Perm, 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.
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 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.
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. Others say that humans have not even started to leave their biggest impact on Earth, and therefore the Anthropocene has not even started yet.
The ICS has not officially approved the term as of September 2015. 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 most ancient 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, with the epoch names altered to the early/late format from lower/upper as recommended by the ICS when dealing with chronostratigraphy.
A service providing a Resource Description Framework/Web Ontology Language representation of the timescale is available through the Commission for the Management and Application of Geoscience Information GeoSciML project as a service and at a SPARQL end-point.
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:
The Amazonian is a geologic system and time period on the planet Mars characterized by low rates of meteorite and asteroid impacts and by cold, hyperarid conditions broadly similar to those on Mars today. The transition from the preceding Hesperian period is somewhat poorly defined. The Amazonian is thought to have begun around 3 billion years ago, although error bars on this date are extremely large (~500 million years). The period is sometimes subdivided into the Early, Middle, and Late Amazonian. The Amazonian continues to the present day.Bartonian
Not to be confused with the Bortonian of the New Zealand geologic time scale.The Bartonian is, in the ICS's geologic time scale, a stage or age in the middle Eocene epoch or series. The Bartonian age spans the time between 41.2 and 37.8 Ma. It is preceded by the Lutetian and is followed by the Priabonian age.Basin Groups
Basin Groups refers to 9 subdivisions of the lunar Pre-Nectarian geologic period. It is the second era of the Hadean.Changhsingian
In the geologic time scale, the Changhsingian or Changxingian is the latest age or uppermost stage of the Permian. It is also the upper or latest of two subdivisions of the Lopingian epoch or series. The Changhsingian lasted from 254.14 to 251.902 million years ago (Ma). It was preceded by the Wuchiapingian and followed by the Induan.The greatest mass extinction in the Phanerozoic eon, the Permian–Triassic extinction event, occurred during this age. The extinction rate peaked about a million years before the end of this stage.Global Boundary Stratotype Section and Point
A Global Boundary Stratotype Section and Point, abbreviated GSSP, is an internationally agreed upon reference point on a stratigraphic section which defines the lower boundary of a stage on the geologic time scale. The effort to define GSSPs is conducted by the International Commission on Stratigraphy, a part of the International Union of Geological Sciences. Most, but not all, GSSPs are based on paleontological changes. Hence GSSPs are usually described in terms of transitions between different faunal stages, though far more faunal stages have been described than GSSPs. The GSSP definition effort commenced in 1977. As of 2012, 64 of the 101 stages that need a GSSP have been formally defined.Imbrian
Millions of years before present
The Imbrian is a lunar geologic period divided into two epochs, the Early Imbrian and Late Imbrian.International Commission on Stratigraphy
The International Commission on Stratigraphy (ICS), sometimes referred to by the unofficial name "International Stratigraphic Commission" is a daughter or major subcommittee grade scientific daughter organization that concerns itself with stratigraphy, geological, and geochronological matters on a global scale.
It is a subordinate body of the International Union of Geological Sciences—of which it is the largest body within the organisation—and of which it is essentially a permanent working subcommittee that meets far more regularly than the quadrennial meetings scheduled by the IUGS, when it meets as a congress or membership of the whole.Lunar geologic timescale
The lunar geological timescale (or selenological timescale) divides the history of Earth's Moon into five generally recognized periods: the Copernican, Eratosthenian, Imbrian (Late and Early epochs), Nectarian, and Pre-Nectarian. The boundaries of this time scale are related to large impact events that have modified the lunar surface, changes in crater formation through time, and the size-frequency distribution of craters superposed on geological units. The absolute ages for these periods have been constrained by radiometric dating of samples obtained from the lunar surface. However, there is still much debate concerning the ages of certain key events, because correlating lunar regolith samples with geological units on the Moon is difficult, and most lunar radiometric ages have been highly affected by an intense history of bombardment.Meghalayan
In the geologic time scale, the Meghalayan is the latest age or uppermost stage of the Quaternary. It is also the upper, or latest, of three subdivisions of the Holocene epoch or series. Its Global Boundary Stratotype Section and Point (GSSP) is a Mawmluh cave formation in Meghalaya, northeast India. Mawmluh cave is one of the longest and deepest caves in India, and conditions here were suitable for preserving chemical signs of the transition in ages. The global auxiliary stratotype is an ice core from Mount Logan in Canada.The Meghalayan begins 4,200 years BP, i.e., before 1950 (c. 2250 BCE), leaving open room for the possible creation of the Anthropocene from 1950 forward. The age began with a 200-year drought that impacted human civilizations in Egypt, Greece, Syria, Canaan, Mesopotamia, the Indus Valley and the Yangtze River Valley. "The fact that the beginning of this age coincides with a cultural shift caused by a global climate event makes it unique," according to Stanley Finney, Secretary General of the International Union of Geological Sciences.The age was officially ratified by the International Commission on Stratigraphy in July 2018 along with the Greenlandian and the Northgrippian.Mississippian (geology)
The Mississippian (also known as Lower Carboniferous or Early Carboniferous) is a subperiod in the geologic timescale or a subsystem of the geologic record. It is the earliest/lowermost of two subperiods of the Carboniferous period lasting from roughly 358.9 to 323.2 million years ago. As with most other geochronologic units, the rock beds that define the Mississippian are well identified, but the exact start and end dates are uncertain by a few million years. The Mississippian is so named because rocks with this age are exposed in the Mississippi River valley.
The Mississippian was a period of marine transgression in the Northern Hemisphere: the sea level was so high that only the Fennoscandian Shield and the Laurentian Shield were dry land. The cratons were surrounded by extensive delta systems and lagoons, and carbonate sedimentation on the surrounding continental platforms, covered by shallow seas.In North America, where the interval consists primarily of marine limestones, it is treated as a geologic period between the Devonian and the Pennsylvanian. During the Mississippian an important phase of orogeny occurred in the Appalachian Mountains. It is a major rock-building period named for the exposures in the Mississippi Valley region. The USGS geologic time scale shows its relation to other periods.In Europe, the Mississippian and Pennsylvanian are one more-or-less continuous sequence of lowland continental deposits and are grouped together as the Carboniferous system, and sometimes called the Upper Carboniferous and Lower Carboniferous instead.Nectarian
The Nectarian Period of the lunar geologic timescale runs from 3920 million years ago to 3850 million years ago. It is the period during which the Nectaris Basin and other major basins were formed by large impact events. Ejecta from Nectaris forms the upper part of the densely cratered terrain found in lunar highlands.
Millions of years before presentNew Zealand geologic time scale
While also using the international geologic time scale, many nations - especially those with isolated and therefore non-standard prehistories - use their own system of dividing geologic time into epochs and faunal stages.
In New Zealand, these epochs and stages use local place names (mainly Maori in origin) back to the Permian. Prior to this time, they largely use the same terms as used in the Australian geologic time scale, and are not divided into epochs. In practice, these early terms are rarely used, as most New Zealand geology is of more recent origin. In all cases, New Zealand uses the same periods as used internationally; it is only the subdivisions of these periods that have been renamed. Very few epochs and stages cross international period boundaries. Of those that do, almost all are within the Cenozoic Era.
Though the New Zealand geologic time scale has not been formally adopted, it has become widely used by New Zealand earth scientists, geologists and palaeontologists since its proposal by J. S. Crampton in 1995.
A standard abbreviation is also used for these epochs and stages, mostly in the form Xx where the first letter is the initial letter of the epoch and the second (lower-case) letter is the initial letter of the stage. These are listed alongside the stage names in the list below.
Currently, we are in the Haweran stage of the Wanganui epoch. The Haweran, which started some 340,000 years ago, is named after the North Island town of Hawera.Northgrippian
In the geologic time scale, the Northgrippian is the middle of the three ages of the Holocene epoch which lies in the Quaternary period. It was officially ratified by the International Commission on Stratigraphy in July 2018 along with the Greenlandian and the Meghalayan.The age began 8,236 years prior to the year 2000 (6236 BCE), and goes up to the start of the Meghalayan, which began 4,200 years prior to the year 1950 (2250 BCE).Piacenzian
The Piacenzian is in the international geologic time scale the upper stage or latest age of the Pliocene. It spans the time between 3.6 ± 0.005 Ma and 2.588 ± 0.005 Ma (million years ago). The Piacenzian is after the Zanclean and is followed by the Gelasian (part of the Pleistocene).
The Piacenzian is roughly coeval with the European land mammal age MN 16, overlaps the late Chapadmalalan and early Uquian South American land mammal age and falls inside the more extensive Blancan North American land mammal age. It also correlates with the Astian, Redonian, Reuverian and Romanian regional stages of Europe. Some authorities describe the British Red Crag Formation and Waltonian stage as late Piacenzian, while others regard them as early Pleistocene.Pliocene
The Pliocene ( ; also Pleiocene) Epoch is the epoch in the geologic timescale that extends from 5.333 million to 2.58 million years BP. It is the second and youngest epoch of the Neogene Period in the Cenozoic Era. The Pliocene follows the Miocene Epoch and is followed by the Pleistocene Epoch. Prior to the 2009 revision of the geologic time scale, which placed the four most recent major glaciations entirely within the Pleistocene, the Pliocene also included the Gelasian stage, which lasted from 2.588 to 1.806 million years ago, and is now included in the Pleistocene.As with other older geologic periods, the geological strata that define the start and end are well identified but the exact dates of the start and end of the epoch are slightly uncertain. The boundaries defining the Pliocene are not set at an easily identified worldwide event but rather at regional boundaries between the warmer Miocene and the relatively cooler Pliocene. The upper boundary was set at the start of the Pleistocene glaciations.Pre-Nectarian
The pre-Nectarian period of the lunar geologic timescale runs from 4.533 billion years ago (the time of the initial formation of the Moon) to 3.920 billion years ago, when the Nectaris Basin was formed by a large impact. It is followed by the Nectarian period.Precambrian
The Precambrian (or Pre-Cambrian, sometimes abbreviated pЄ, or Cryptozoic) is the earliest part of Earth's history, set before the current Phanerozoic Eon. The Precambrian is so named because it preceded the Cambrian, the first period of the Phanerozoic eon, which is named after Cambria, the Latinised name for Wales, where rocks from this age were first studied. The Precambrian accounts for 88% of the Earth's geologic time.
The Precambrian (colored green in the timeline figure) is an informal unit of geologic time, subdivided into three eons (Hadean, Archean, Proterozoic) of the geologic time scale. It spans from the formation of Earth about 4.6 billion years ago (Ga) to the beginning of the Cambrian Period, about 541 million years ago (Ma), when hard-shelled creatures first appeared in abundance.Quaternary
Quaternary ( ) is the current and most recent of the three periods of the Cenozoic Era in the geologic time scale of the International Commission on Stratigraphy (ICS). It follows the Neogene Period and spans from 2.588 ± 0.005 million years ago to the present. The Quaternary Period is divided into two epochs: the Pleistocene (2.588 million years ago to 11.7 thousand years ago) and the Holocene (11.7 thousand years ago to today). The informal term "Late Quaternary" refers to the past 0.5–1.0 million years.The Quaternary Period is typically defined by the cyclic growth and decay of continental ice sheets associated with Milankovitch cycles and the associated climate and environmental changes that occurred.Zanclean
The Zanclean is the lowest stage or earliest age on the geologic time scale of the Pliocene. It spans the time between 5.332 ± 0.005 Ma and 3.6 ± 0.005 Ma (million years ago). It is preceded by the Messinian age of the Miocene epoch, and followed by the Piacenzian age.
The Zanclean can be correlated with regionally used stages, such as the Tabianian or Dacian of Central Europe. It also corresponds to the late Hemphillian to mid-Blancan North American Land Mammal Ages. In California, the Zanclean roughly corresponds to the mid-Delmontian Californian Stage of from 7.5 To 2.9 Ma ago.
|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.||0.126|
|Middle ('Ionian', 'Chibanian')||High amplitude 100 ka glacial cycles. Rise of Homo sapiens.||0.781|
|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. Australopithecus common in East Africa.||3.6*|
|Zanclean||Zanclean flooding of the Mediterranean Basin. Cooling climate. 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; Gradual separation of human and chimpanzee ancestors. Sahelanthropus tchadensis in Africa.||7.246*|
|Serravallian||Warmer during Middle Miocene Climate Optimum. Extinctions in Middle Miocene disruption.||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 mammal and bird families become recognizable. Horses and mastodons diverse. Grasses become ubiquitous. Ancestor of apes and humans.||20.44|
|Paleogene||Oligocene||Chattian||Grande Coupure extinction. Start of widespread Antarctic glaciation. Rapid evolution and diversification of fauna, especially mammals. Major evolution and dispersal of modern types of flowering plants||28.1|
|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. First grasses. 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 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 primitive 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.||59.2*|
|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, duck bills, and horned dinosaurs) evolve on land, as do Eusuchia (modern crocodilians); and mosasaurs and modern sharks appear in the sea. Primitive birds gradually replace pterosaurs. 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|
|Jurassic||Late||Tithonian||Gymnosperms (especially conifers, Bennettitales and cycads) and ferns common. Many types of dinosaurs, such as sauropods, carnosaurs, and stegosaurs. Mammals common but small. First birds and lizards. Ichthyosaurs and plesiosaurs 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[f]).||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 dinosaurs, in the oceans as Ichthyosaurs and nothosaurs, and in the air as pterosaurs. Cynodonts become smaller and more mammal-like, while first mammals and crocodilia appear. Dicroidiumflora common on land. Many large aquatic temnospondyl amphibians. 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|
|Induan||251.902 ± 0.06*|
|Paleozoic||Permian||Lopingian||Changhsingian||Landmasses unite into supercontinent Pangaea, creating the Appalachians. End of Permo-Carboniferous glaciation. Synapsid reptiles (pelycosaurs and therapsids) become plentiful, 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. 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*|
|Pennsylvanian||Gzhelian||Winged insects radiate suddenly; some (esp. Protodonata and Palaeodictyoptera) are quite large. Amphibians common and diverse. First reptiles and 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.||303.7 ± 0.1|
|Kasimovian||307 ± 0.1|
|Moscovian||315.2 ± 0.2|
|Bashkirian||323.2 ± 0.4*|
|Mississippian||Serpukhovian||Large primitive trees, first land vertebrates, and amphibious sea-scorpions live amid coal-forming coastal swamps. Lobe-finned rhizodonts are dominant big fresh-water predators. 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.||330.9 ± 0.2|
|Viséan||346.7 ± 0.4*|
|Tournaisian||358.9 ± 0.4*|
|Devonian||Late||Famennian||First clubmosses, horsetails and ferns appear, as do the first seed-bearing plants (progymnosperms), first trees (the progymnosperm Archaeopteris), and first (wingless) insects. Strophomenid and atrypid 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) rule the seas. First amphibians still aquatic. "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 (the rhyniophytes and their relatives), first millipedes and arthropleurids on land. First jawed fishes, as well as many armoured jawless fish, 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. Conodonts (early planktonic vertebrates) appear. First green plants and fungi on land. Ice age at end of period.||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 life in the Cambrian Explosion. Numerous fossils; most modern animal phyla appear. First chordates appear, along with a number of extinct, problematic phyla. 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. Gondwana emerges. Petermann Orogeny on the Australian continent tapers off (550–535 Ma). Ross Orogeny in Antarctica. Adelaide Geosyncline (Delamerian Orogeny), majority of orogenic activity from 514–500 Ma. Lachlan Orogeny on Australian continent, c. 540–440 Ma. Atmospheric CO2 content roughly 15 times present-day (Holocene) levels (6000 ppmv compared to today's 400 ppmv)[f]||~489.5|
|Series 2||Stage 4||~514|
|Fortunian||~541 ± 1.0*|
|Precambrian[h]||Proterozoic[i]||Neoproterozoic[i]||Ediacaran||Good fossils of the first multi-celled animals. Ediacaran biota flourish worldwide in seas. Simple trace fossils of possible worm-like Trichophycus, etc. First sponges and trilobitomorphs. 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.||~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. Adelaide Geosyncline laid down on Australian continent, beginning of Adelaide Geosyncline (Delamerian Orogeny) in Australia.||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. 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).||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. Earliest evidence for life based on unusually high amounts of light isotopes of carbon, a common sign of life.||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|
(541.0 Mya–2.5 Gya)
|Archean eon (2.5–4 Gya)|
|Hadean eon (4–4.6 Gya)|