Geologic time scale

Geologic time scale proportionally represented as a log-spiral. The image also shows some notable events in Earth's history and the general evolution of life.

The geologic time scale, proportionally represented as a log-spiral with some major events in Earth's history. A megaannum (Ma) represents one million (10⁶) years.

The geologic time scale or geological time scale describes how geologic time is divided into standardised intervals. It uses the rock record together with the principles of chronostratigraphy to place rock sequences into their relative age positions, and geochronology techniques, such as radiometric dating, to precisely date the boundaries between them. It is used primarily by Earth scientists (including geologists, paleontologists, geophysicists, geochemists, and paleoclimatologists) to describe the timing and relationships of events in geologic history. The time scale has been developed through the study of rock layers and the observation of their relationships and identifying features such as lithologies, paleomagnetic properties, and fossils. The definition of standardised international units of geological time is the responsibility of the International Commission on Stratigraphy (ICS), a constituent body of the International Union of Geological Sciences (IUGS), whose primary objective is to precisely define global chronostratigraphic units of the International Chronostratigraphic Chart (ICC)Template:Ref icc that are used to define divisions of geological time. The chronostratigraphic divisions are in turn used to define geochronologic units.

Principles

See also: Age of Earth, History of Earth, and Geological history of Earth

The geologic time scale is a way of representing deep time based on events that have occurred throughout Earth's history, a time span of about 4.54 ± 0.05 billion years. It arranges the rock record in chronological order by observing fundamental changes in stratigraphy that correspond to major geological or paleontological events. It combines the disciplines of chronostratigraphy, which studies the relationships between rock sequences to determine their relative ages, and geochronology, the science of dating rocks and other geological materials.

Chronostratigraphy

Chronostratigraphy is the branch of stratigraphy that organises all the rocks of the Earth's crust into groups, known as chronostratigraphic units, based on their relative ages. A chronostratigraphic unit includes all rock sequences globally that were deposited during a particular time interval.

Chronostratigraphy uses several key principles to determine the relative relationships of rocks and thus their chronostratigraphic position in the rock record.

• The law of superposition that states that in undeformed stratigraphic sequences the oldest strata will lie at the bottom of the sequence, while newer material stacks upon the surface. In practice, this means a younger rock will lie on top of an older rock unless there is evidence to suggest otherwise.
• The principle of original horizontality that states layers of sediments will originally be deposited horizontally under the action of gravity. However, it is now known that not all sedimentary layers are deposited purely horizontally, but this principle is still a useful concept.
• The principle of lateral continuity that states layers of sediments extend laterally in all directions until either thinning out or being cut off by a different rock layer, i.e. they are laterally continuous. Layers do not extend indefinitely; their limits are controlled by the amount and type of sediment in a sedimentary basin, and the geometry of that basin.
• The principle of cross-cutting relationships that states a rock that cuts across another rock must be younger than the rock it cuts across.
• The law of included fragments that states small fragments of one type of rock that are embedded in a second type of rock must have formed first, and were included when the second rock was forming.
• The relationships of unconformities which are geologic features representing a gap in the geologic record. Unconformities are formed during periods of erosion or non-deposition, indicating non-continuous sediment deposition. Observing the type and relationships of unconformities in strata allows geologist to understand the relative timing of the strata.
• The principle of faunal succession (where applicable) that states rock strata contain distinctive sets of fossils that succeed each other vertically in a specific and reliable order. This allows for a correlation of strata even when the horizon between them is not continuous.

Geochronology

Geochronology is the study of geological time. It uses quantitative measurements (geochronometry), such as radiometric dating, to provide precise ages, and relative methods of dating (e.g. paleomagnetism and stable isotope ratios) to establish a timeframe for events in Earth's history. A geochronologic unit is an interval of time during which a chronostratigraphic unit formed. For example, all the rocks of the Silurian System (a chronostratigraphic unit) were deposited during the Silurian Period (a geochronologic unit).

The age of a geochronologic unit can be refined and changed by improved dating techniques. However, the equivalent chronostratigraphic unit boundary remains unchanged. For example, in early 2022, the base of the Cambrian Period (a geochronologic unit) was revised from 541 Ma to 538.8 Ma but the rock definition of the boundary (GSSP) at the base of the Cambrian, and thus the boundary between the Ediacaran and Cambrian systems (chronostratigraphic units) has not been changed; rather, the absolute age has merely been refined.

Global Boundary Stratotype Section and Point (GSSP)

Historically, regional geologic time scales were used due to the litho- and biostratigraphic differences around the world in time equivalent rocks. The ICS has long worked to reconcile conflicting terminology by standardising globally significant and identifiable stratigraphic horizons that can be used to define the lower boundaries of chronostratigraphic units. A Global Boundary Stratotype Section and Point (GSSP) defines the lower boundary of a stage as being at a precise point in a specific rock succession in a particular geographic location. These reference points are known informally as "golden" spikes. All the beds above the spike belong to one time interval and all those below it to another. This allows beds of a similar age around the world to be correlated with the strata that contain the golden spike. For example, the iridium anomaly produced by the Chicxulub asteroid impact marks the lower boundary of the Paleogene System and thus the boundary between the Cretaceous and Paleogene. Whilst the GSSP is defined at Oued Djerfane in Tunisia, strata containing the iridium anomaly are found worldwide.

The Proterozoic (apart from the Ediacaran), Archean and Hadean are subdivided by absolute ages (Global Standard Stratigraphic Ages) rather than geological features. Proposals have been made to better reconcile these divisions with the rock record.

Divisions of geologic time

See also: Stratigraphy, Chronostratigraphy, Biostratigraphy, Magnetostratigraphy, Lithostratigraphy, and Geochronology

The standard international units of the geologic time scale are published by the International Commission on Stratigraphy on the International Chronostratigraphic Chart. However, regional terms are still in use in some areas. The numeric values on the International Chronostratigraphic Chart are represented by the unit Ma (megaannum, for 'million years'). For example, 201.3 Template:Period start error Ma, the lower boundary of the Jurassic Period, is defined as 201,400,000 years old with an uncertainty of 200,000 years. Other SI prefix units commonly used by geologists are Ga (gigaannum, billion years), and ka (kiloannum, thousand years), with the latter often represented in calibrated units (before present).

The geologic time scale is divided into chronostratigraphic units and their corresponding geochronologic units:

• An eon is the largest geochronologic time unit and is equivalent to a chronostratigraphic eonothem. There are four formally defined eons: the Hadean, Archean, Proterozoic and Phanerozoic.
• An era is the second largest geochronologic time unit and is equivalent to a chronostratigraphic erathem. There are ten defined eras: the Eoarchean, Paleoarchean, Mesoarchean, Neoarchean, Paleoproterozoic, Mesoproterozoic, Neoproterozoic, Paleozoic, Mesozoic and Cenozoic, with none from the Hadean eon.
• A period is equivalent to a chronostratigraphic system. There are 22 defined periods, with the current being the Quaternary period. As an exception, two subperiods are used for the Carboniferous Period.
• An epoch is the second smallest geochronologic unit. It is equivalent to a chronostratigraphic series. There are 37 defined epochs and one informal one. The current epoch is the Holocene. There are also 11 subepochs which are all within the Neogene and Quaternary. The use of subepochs as formal units in international chronostratigraphy was ratified in 2022.
• An age is the smallest hierarchical geochronologic unit. It is equivalent to a chronostratigraphic stage. There are 96 formal and five informal ages. The current age is the Meghalayan.
• A chron is a non-hierarchical formal geochronology unit of unspecified rank and is equivalent to a chronostratigraphic chronozone. These correlate with magnetostratigraphic, lithostratigraphic, or biostratigraphic units as they are based on previously defined stratigraphic units or geologic features.

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

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

The subdivisions Early and Late are used as the geochronologic equivalents of the chronostratigraphic Lower and Upper, e.g., Early Triassic Period (geochronologic unit) is used in place of Lower Triassic System (chronostratigraphic unit).

Naming of geologic time

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

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

History of the geologic time scale

See also: History of geology and History of paleontology

Early history

The most modern geological time scale was not formulated until 1911 by Arthur Holmes (1890 – 1965), who drew inspiration from James Hutton (1726–1797), a Scottish Geologist who presented the idea of uniformitarianism or the theory that changes to the Earth's crust resulted from continuous and uniform processes. The broader concept of the relation between rocks and time can be traced back to (at least) the philosophers of Ancient Greece from 1200 BC to 600 AD. Xenophanes of Colophon (c. 570–487 BCE) observed rock beds with fossils of seashells located above the sea-level, viewed them as once living organisms, and used this to imply an unstable relationship in which the sea had at times transgressed over the land and at other times had regressed. This view was shared by a few of Xenophanes's scholars and those that followed, including Aristotle (384–322 BC) who (with additional observations) reasoned that the positions of land and sea had changed over long periods of time. The concept of deep time was also recognized by Chinese naturalist Shen Kuo (1031–1095) and Islamic scientist-philosophers, notably the Brothers of Purity, who wrote on the processes of stratification over the passage of time in their treatises. Their work likely inspired that of the 11th-century Persian polymath Avicenna (Ibn Sînâ, 980–1037) who wrote in The Book of Healing (1027) on the concept of stratification and superposition, pre-dating Nicolas Steno by more than six centuries. Avicenna also recognized fossils as "petrifications of the bodies of plants and animals", with the 13th-century Dominican bishop Albertus Magnus (c. 1200–1280), who drew from Aristotle's natural philosophy, extending this into a theory of a petrifying fluid. These works appeared to have little influence on scholars in Medieval Europe who looked to the Bible to explain the origins of fossils and sea-level changes, often attributing these to the 'Deluge', including Ristoro d'Arezzo in 1282. It was not until the Italian Renaissance when Leonardo da Vinci (1452–1519) would reinvigorate the relationships between stratification, relative sea-level change, and time, denouncing attribution of fossils to the 'Deluge':

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

File:Sketch of the Succession pf Strata and their relative Altitudes.jpg

Sketch of the Succession of Strata and their Relative Altitudes (William Smith)

These views of da Vinci remained unpublished, and thus lacked influence at the time; however, questions of fossils and their significance were pursued and, while views against Genesis were not readily accepted and dissent from religious doctrine was in some places unwise, scholars such as Girolamo Fracastoro shared da Vinci's views, and found the attribution of fossils to the 'Deluge' absurd. Although many theories surrounding philosophy and concepts of rocks were developed in earlier years, "the first serious attempts to formulate a geological time scale that could be applied anywhere on Earth were made in the late 18th century." Later, in the 19th century, academics further developed theories on stratification. William Smith, often referred to as the "Father of Geology" developed theories through observations rather than drawing from the scholars that came before him. Smith's work was primarily based on his detailed study of rock layers and fossils during his time and he created "the first map to depict so many rock formations over such a large area". After studying rock layers and the fossils they contained, Smith concluded that each layer of rock contained distinct material that could be used to identify and correlate rock layers across different regions of the world. Smith developed the concept of faunal succession or the idea that fossils can serve as a marker for the age of the strata they are found in and published his ideas in his 1816 book, "Strata identified by organized fossils."

Establishment of primary principles

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

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

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

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

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

Formulation of a modern geologic time scale

The apparent, earliest formal division of the geologic record with respect to time was introduced during the era of Biblical models by Thomas Burnet who applied a two-fold terminology to mountains by identifying "montes primarii" for rock formed at the time of the 'Deluge', and younger "monticulos secundarios" formed later from the debris of the "primarii". Anton Moro (1687–1784) also used primary and secondary divisions for rock units but his mechanism was volcanic. In this early version of the Plutonism theory, the interior of Earth was seen as hot, and this drove the creation of primary igneous and metamorphic rocks and secondary rocks formed contorted and fossiliferous sediments. These primary and secondary divisions were expanded on by Giovanni Targioni Tozzetti (1712–1783) and Giovanni Arduino (1713–1795) to include tertiary and quaternary divisions. These divisions were used to describe both the time during which the rocks were laid down, and the collection of rocks themselves (i.e., it was correct to say Tertiary rocks, and Tertiary Period). Only the Quaternary division is retained in the modern geologic time scale, while the Tertiary division was in use until the early 21st century. The Neptunism and Plutonism theories would compete into the early 19th century with a key driver for resolution of this debate being the work of James Hutton (1726–1797), in particular his Theory of the Earth, first presented before the Royal Society of Edinburgh in 1785. Hutton's theory would later become known as uniformitarianism, popularised by John Playfair (1748–1819) and later Charles Lyell (1797–1875) in his Principles of Geology. Their theories strongly contested the 6,000 year age of the Earth as suggested determined by James Ussher via Biblical chronology that was accepted at the time by western religion. Instead, using geological evidence, they contested Earth to be much older, cementing the concept of deep time.

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

The advent of geochronometry

File:Pierre Lecomte du Noüy - LES AGES DE LA VIE SUR LA TERRE - in L'Homme et sa destinée - 1947.jpg

One example of an obsolete geological time scale (France, mid-1940s).

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

The discovery of radioactive decay by Henri Becquerel, Marie Curie, and Pierre Curie laid the ground work for radiometric dating, but the knowledge and tools required for accurate determination of radiometric ages would not be in place until the mid-1950s. Early attempts at determining ages of uranium minerals and rocks by Ernest Rutherford, Bertram Boltwood, Robert Strutt, and Arthur Holmes, would culminate in what are considered the first international geological time scales by Holmes in 1911 and 1913. The discovery of isotopes in 1913 by Frederick Soddy, and the developments in mass spectrometry pioneered by Francis William Aston, Arthur Jeffrey Dempster, and Alfred O. C. Nier during the early to mid-20th century would finally allow for the accurate determination of radiometric ages, with Holmes publishing several revisions to his geological time-scale with his final version in 1960.

Modern international geological time scale

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

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

Table of geologic time

The following table summarises the major events and characteristics of the divisions making up the geologic time scale of Earth. This table is arranged with the most recent geologic periods at the top, and the oldest at the bottom. The height of each table entry does not correspond to the duration of each subdivision of time. As such, this table is not to scale and does not accurately represent the relative time-spans of each geochronologic unit. While the Phanerozoic Eon looks longer than the rest, it merely spans ~538.8 Ma (~11.8% of Earth's history), whilst the previous three eons collectively span ~4,028.2 Ma (~88.2% of Earth's history). This bias toward the most recent eon is in part due to the relative lack of information about events that occurred during the first three eons compared to the current eon (the Phanerozoic). The use of subseries/subepochs has been ratified by the ICS.

While some regional terms are still in use, the table of geologic time conforms to the nomenclature, ages, and colour codes set forth by the International Commission on Stratigraphy in the official International Chronostratigraphic Chart.

Eonothem/ Eon	Erathem/ Era	System/ Period	Series/ Epoch	Stage/ Age	Major events	Start, million years ago
Phanerozoic	Cenozoic	Quaternary	Holocene	Meghalayan	4.2 ka cool period, dry climate leads to decline of agriculture-related civilisations in Egypt, Mesopotamia and India. Medieval Warm Period (about 900 - 1350 CE) and Little Ice Age (about 1400 to 1900 CE). Rapidly warming climate as CO2 added to atmosphere from burning fossil fuels.	0.0042 Template:Period start error*
				Northgrippian	8.2 ka cool period, followed by warming climate with melting ice raising sea levels. Doggerland and Sundaland flooded.	0.0082 Template:Period start error*
				Greenlandian	Younger Dryas and Last Glacial Period end. Rise of agriculture. Extinction of Pleistocene megafauna.	0.0117 Template:Period start error*
			Pleistocene	Upper/Late ('Tarantian')	Eemian Interglacial Stage followed by the Last Glacial Period. After Last Glacial Maximum (about 25 – 15 ka) climate begins to warm. Younger Dryas final cold period of ice age. Toba supervolcano eruption. Homo sapiens spread across the globe. Homo floresiensis live on island of Flores. Homo neanderthalensis go extinct.	0.129 Template:Period start error
				Chibanian	Brunhes–Matuyama geomagnetic reversal event. Homo heidelbergensis evolves in Africa and spreads to Europe. Homo neanderthalensis appear in western Eurasia. Homo sapiens evolve in Africa. Homo erectus and Homo heidelbergensis die out.	0.774Template:Period start error*
				Calabrian	Mid Pleistocene transition: glacial/interglacial frequency slows to every 100,000 years. Glacial periods now long enough for continental ice-sheets beyond polar regions. Chimpanzees and bonobos diverge. Homo erectus spreads through Eurasia. Homo habilis goes extinct.	1.8 Template:Period start error*
				Gelasian	Start of Pleistocene Ice Age: 40,000 year cycles of glacials/interglacials with ice cap growth and retreat, and sea level falls and rises. Rise of Pleistocene megafauna. Homo habilis and Homo erectus evolve in Africa.	2.58 Template:Period start error*
		Neogene	Pliocene	Piacenzian	Isthmus of Panama land bridge forms between North and South America blocking equatorial ocean currents between Atlantic and Pacific oceans. Gulf Stream develops as Atlantic waters divert northward. Global temperatures warm melting polar ice caps and sea levels rise flooding continental margins. Temperatures drop at 2.7 Ma and the Pleistocene Ice Age begins. First modern big cats and modern horses. Tortoises and finch-billed tanagers arrive in the Galapagos. Earliest humans appear.	3.6 Template:Period start error*
				Zanclean	Straits of Gibraltar form as Atlantic waters flood the Mediterranean Sea basin (Zanclean flood). Global climate continues to cool. Asian elephants appear. Hominins Ardipithecus, Australopithecus and Paranthropus evolve.	5.333 Template:Period start error*
			Miocene	Messinian	Connection between Mediterranean Sea and Atlantic is blocked, resulting in Messinian salinity crisis with evaporites accumulating across Mediterranean as its waters dry up. Collision of Banda Arc with Australia and Timor begins. Global climate cools and permanent ice cap forms in Arctic. Sea levels drop as ice sheets grow. Spread of C4 grasses result in extinction of many herbivores. Sea snakes evolve. Gorilla-human-chimpanzee lineages split, then chimpanzees and humans diverge. Earliest hominid Sahelanthropus.	7.246 Template:Period start error*
				Tortonian		11.63 Template:Period start error*
				Serravallian	Australia begins to collide with Southeast Asia, blocking equatorial circulation between western Pacific and Indian Oceans. Antarctic ice cap shrinks as global temperatures warm (Middle Miocene climatic optimum). Last creodonts (early predatory mammals) become extinct. Megalodon (giant shark) evolves.	13.82 Template:Period start error*
				Langhian		15.97 Template:Period start error*
				Burdigalian	The Tian Shan and Altai mountains, Central Asia, form (Himalayan orogeny). Columbia River Basalt large igneous province (LIP) eruptions above rising Yellowstone hotspot, North America. Climate continues to cool. Compositae (herbaceous plants) appear and rapidly diversify, triggering evolutionary radiations in rodents, snakes (first vipers appear) and songbirds. First gibbons and orangutans. First modern dolphins.	20.44 Template:Period start error
				Aquitanian		23.03 Template:Period start error*
		Paleogene	Oligocene	Chattian	North America and Eurasia plate boundary established along Mid-Atlantic Ridge. Central American volcanic arc begins to collide with South America. East African LIP eruptions begin as Afar mantle plume rises. Late Cenozoic Ice Age begins. Rapid growth of the Antarctic ice cap produces major drop in global sea levels. Grasslands and prairies thrive as climate dries. Paraceratherium largest ever land mammal flourishes. First felids (cats), mustelids (e.g. weasels, otters, badgers), and pinnipeds (seals, sea lions and walruses). Whales split into toothed and filter feeders. Multituberculates (rat-like early mammals) go extinct.	28.1 Template:Period start error*
				Rupelian		33.9 Template:Period start error*
			Eocene	Priabonian	Subduction in the Mediterranean leads to Tell-Rif-Betic, Dinarides, Hellenides and Taurides (Alpine) orogenies. Eurekan orogeny, Greenland. Zagros orogeny as Arabia and Eurasia collide. Laramide orogeny ends. Gulf of Aden forms between Africa and Asia. Cooling climate with brief warm period. End Eocene Australia and South America move away from Antarctica opening Drake and Tasmanian passages. Antarctic Circumpolar current forms. Rapid drop in global temperatures. Ice sheets on Antarctica. Canids (wolves and foxes), Catarrhine primates (old world monkeys and apes), and raptors evolve. Basilosaurus is first fully aquatic whale.	37.8 Template:Period start error*
				Bartonian		41.2 Template:Period start error
				Lutetian		47.8 Template:Period start error*
				Ypresian	Greenland separates from Eurasia and Eurasian Basin opens in Arctic. Greater India collides with southern Eurasia, beginning Himalayan orogeny. North Atlantic LIP eruptions continue. Major reorganisation of plate motions across Pacific region initiates Izu-Bonin-Mariana and Tonga-Kermadec subduction zones. Greenhouse temperatures continue from Paleocene-Eocene Thermal Maximum (PETM) as climate affected by North Atlantic LIP eruptions, but global cooling begins from about 50 Ma with changing paleogeography and oceanography conditions. Angiosperms (flowering plants) evolve larger fruits. First songbirds, parrots and woodpeckers. Primates divide into strepsirrhines (lemurs and lorises) and haplorhines (tarsiers and anthropoids). Artiodactyls (even-toed ungulates) appear and split into Cetruminantia (ruminants, whales and dolphins), Suina (pigs), and Tylopoda (camels and relatives). First Carnivora (meat-eating mammals). Mice, rats, bats and tapirs appear. Eohippus earliest member of horse family. Marsupials reach Australia.	56 Template:Period start error*
			Paleocene	Thanetian	Alpine orogeny develops as Neotethys closes and Africa begins collision with Eurasia. Pyrenean and Laramide orogenies continue. India drifts rapidly northwards. North Atlantic LIP eruptions start as Proto-Icelandic mantle plume rises. Subduction zones form along margins of Caribbean plate. Bering Straits land bridge present during low sea level periods. Chicxulub impact causes "impact winter", then climate warms with final eruption of the Deccan Traps before cool, dry conditions re-established. Rapid rise in global temperatures at onset of PETM due to North Atlantic LIP eruptions. End-Cretaceous mass extinction about 75% of plant and animal species go extinct, including ammonoids, rudist molluscs, non-avian dinosaurs, plesiosaurs, mosasaurs and pterosaurs. Mammals evolve quickly filling vacant ecological niches, modern groups of birds diversify and angiosperms become dominant form of plant life. First earthworms and land turtles. Phorusrhacidae (terror birds) and creodonts (early predatory mammals) evolve. Perissodactyls (odd-toed ungulates) appear and diversify. First primates, proboscideans (elephants), Xenartha (sloths, anteaters and armadillos) and rodents.	59.2 Template:Period start error*
				Selandian		61.6 Template:Period start error*
				Danian		66 Template:Period start error*
	Mesozoic	Cretaceous	Upper/Late	Maastrichtian	Pangaea continues to fragment. Africa and South America separate as seafloor spreading established in South Atlantic. India and Australia move away from Antarctica, and India separates from Madagascar. Central Atlantic propagates north. |Pyrenean orogeny begins as Iberia rotates relative to Eurasia. Africa moves northwards. Sevier and Laramide orogenies, western North America. LIP eruptions include: Ontong Java-Nui; Kerguelen; High Arctic and Deccan Traps. Highest sea levels in the Phanerozoic, shallow seas extend across large areas of the continents. Greenhouse climate global average temperature peaks c. 28 °C in the Cenomanian-Turonian. Tropical plants and dinosaurs on Antarctica and above Arctic Circle. Oceanic anoxic events (OAEs) result in widespread deposition of organic-rich black shales. Calcareous foraminifera and coccolithophores flourish forming massive chalk deposits. Teleost (bony fish) radiate. Predators grow large: plesiosaurs and mosasaurs in the sea; carcharodontosaurs and tyrannosaurs on land. Modern lobsters, crabs, shrimps and crocodiles appear. First bees, termites, ants, fleas, mantids and snakes. Angiosperms (flowering plants) proliferate and develop symbiotic relationships with insects. First grasses. Woody angiosperms evolve including rose, magnolia and sycamore families. First marsupials and monotremes. End of the Cretaceous is marked by the Chicxulub impact event and the Cretaceous-Paleogene mass extinction.	72.1 Template:Period start error*
				Campanian		83.6 Template:Period start error*
				Santonian		86.3 Template:Period start error*
				Coniacian		89.8 Template:Period start error*
				Turonian		93.9 Template:Period start error*
				Cenomanian		100.5 Template:Period start error*
			Lower/Early	Albian		~113 Template:Period start error*
				Aptian		~125 Template:Period start error
				Barremian		~129.4 Template:Period start error*
				Hauterivian		~132.9 Template:Period start error*
				Valanginian		~139.8 Template:Period start error*
				Berriasian		~145 Template:Period start error
		Jurassic	Upper/Late	Tithonian	Seafloor spreading in the Central Atlantic between North America and Africa-South America begins break up of Pangaea. Rifting continues in northern Atlantic and Caribbean. Gondwana splits into East and West Gondwana as Somali and Mozambique basins open. Pacific plate forms in central Panthalassa. Cimmerian and Indosinian orogenies continue. Start of Andean tectonic cycle, South America. Nevadan orogeny, North America. Mongol-Okhotsk Ocean closes forming Verkhoyansk-Kolyma mountain belt, Siberia. Neotethys narrows. Greenhouse climate with warmer and cooler periods. Arid conditions across equatorial and subtropical regions; coal and bauxite deposits in wetter temperate belts. Emplacement of Karoo-Ferrar LIP leads to global warming and the widespread Toarcian oceanic anoxic event. Rise in global sea levels. Change from aragonite to calcite seas. First large reefs. Phytoplankton and dinoflagellates diversify. First coccolithophores. Ammonoids and bellomnoids proliferate. Major radiation of sharks. Vieraella earliest true frog. First modern turtles. Cycads dominant forest flora. Also ferns, conifers and ginkgos. Dinosaurs rise to dominance, mammals remain small. First Ornithischia (e.g. stegasaurs and ceratopsians). Sauropods evolve into giants, including brachiosaurs, titanosaurs, and diplodocids. First ceratosaurs, megalosaurs, allosaurs, and coelurosaurs therapods. Coelurosaurs, many with feathers, include early tyrannosaurs and maniraptorans (ancestors of birds). First pterodactyloids.	152.1 Template:Period start error
				Kimmeridgian		157.3 Template:Period start error*
				Oxfordian		163.5 Template:Period start error
			Middle	Callovian		166.1 Template:Period start error
				Bathonian		168.3 Template:Period start error*
				Bajocian		170.3 Template:Period start error*
				Aalenian		174.1 Template:Period start error*
			Lower/Early	Toarcian		182.7 Template:Period start error*
				Pliensbachian		190.8 Template:Period start error*
				Sinemurian		199.3 Template:Period start error*
				Hettangian		201.3 Template:Period start error*
		Triassic	Upper/Late	Rhaetian	Pangaea forms an arc extending from almost pole to pole. Siberian Traps eruptions wane, but hot house climate continues. Cimmerian terranes collide with Eurasia: Indosinian orogeny in east; Cimmerian orogeny in west. Sonoma (western Laurussia), and Hunter-Bowen (Australia) orogenies continue. Late Triassic, emplacement of the Central Atlantic magmatic province (CAMP) followed by seafloor spreading marks start of Pangaea break up. Archosaurs divide into pseudosuchia (crocodiles), and ornithodirans (dinosaurs and pterosaurs). Mammaliaformes evolve from cynodonts. Evidence of endothermy (warm-bloodedness) in dinosaurs and mammals. First teleosts (modern ray-finned fish). Ichthyosaurs, and sauropterygians plesiosaurs, nothosaurs, placodonts) appear. First scleractinian (hard coral) reefs. First wasps and stick insects. Late Triassic eruptions of Wrangellia LIP raises temperatures, intensifies Pangaea monsoons and increases rainfall (Carnian pluvial episode). Bennettitales, modern ferns and conifers appear. First Lepidoptera (moths and butterflies). Modern groups of phytoplankton appear. Manicouagan bolide impact reduces global temperatures, before CAMP eruptions increases them and triggers Triassic-Jurassic mass extinction. Major loss of reef ecosystems, reduction in marine genera, conodonts die out. Major changes in terrestrial flora. Loss of vertebrate genera, including non-mammalian therapsids. Crocodylomorphs only pseudosuchians to survive.	~208.5 Template:Period start error
				Norian		~227 Template:Period start error
				Carnian		~237 Template:Period start error*
			Middle	Ladinian		~242 Template:Period start error*
				Anisian		247.2 Template:Period start error
			Lower/Early	Olenekian		251.2 Template:Period start error
				Induan		251.902 Template:Period start error*
	Paleozoic	Permian	Lopingian	Changhsingian	Pangaea at its maximum extent. Ural and Alleghanian orogenies continue. Hunter-Bowen orogeny, eastern Australia; Sonoma orogeny, western Laurussia. Kazakhstania and Tarim collide with Siberia. Orogenic collapse of Variscan orogeny and early extension along the lines of the future Atlantic, Indian and Southern Oceans. Opening of Neo-Tethys Ocean as Cimmerian terranes rift from northeast Gondwana. Late Paleozoic Ice Age wanes and humid, icehouse climate give way to arid, greenhouse conditions. Global average temperatures rise from c. 12° to over 30° at Permo-Triassic boundary. Desert dune sands and evaporites dominate interior of Pangea. Coal swamps at high latitudes and humid coastal regions. Mosses, Coleoptera (beetles) and Diptera (two-winged flies) appear. Diapsids split into archosaurs (crocodiles and dinosaurs) and lepidosaurs (lizards and snakes). First marine reptiles. Therapsids and cynodonts evolve from synapsids. Guadalupian-Lopingian boundary mass extinction linked to eruption of Emeishan LIP, South China. At the Permo-Triassic boundary, eruption of the Siberian Traps LIP releases vast amounts of CO2 leading to extreme global warming, and the end-Permian mass extinction. Anoxic waters from the deep ocean move up to the shallows, eliminating trilobites, rugose and tabulate corals, and placoderms. Brachiopods, ammonoids, sharks, bony fish, and crinoids see major reductions. On land, forests disappear. Palaeodictyopterida and many insect groups go extinct, as do all non-therapsid synapsids and most therapsid genera.	254.14 Template:Period start error*
				Wuchiapingian		259.1 Template:Period start error*
			Guadalupian	Capitanian		265.1 Template:Period start error*
				Wordian		268.8 Template:Period start error*
				Roadian		272.95 Template:Period start error*
			Cisuralian	Kungurian		283.5 Template:Period start error
				Artinskian		290.1 Template:Period start error*
				Sakmarian		295 Template:Period start error*
				Asselian		298.9 Template:Period start error*
		Carboniferous	Pennsylvanian	Gzhelian	Continuation of the Variscan orogeny (Ouachita and Alleghanian orogenies) with growth of the Central Pangean Mountains. Ural orogeny continues with continental collision between Kazakhstania and Laurussia. Humid, coal swamps form in foreland basins of the Central Pangean Mountains and around North and South China cratons. As the Late Paleozoic icehouse (LPIA) continues, waxing and waning of ice sheets causes rapid changes in global sea level, flooding these regions and depositing cyclothem sequences. Atmospheric oxygen levels rise to over 25% before decreasing again. Appearance of aragonite reef builders, including algae and sponges. Freshwater Eurypterids (sea scorpions). On land, Neoptera appear, and Miomoptera show earliest evidence for complete metamorphosis. First true terrestrial amphibians. Amniotes appear and split into two groups: sauropsids (reptiles) and synapsids (mammals). Lepidodendron and Sigillaria lycopod trees dominate coal swamps, with smaller sphenopsids (horsetails) and seed ferns between. Gymnosperms, including conifers and cycads grow on drier ground. LPIA peaks at Carboniferous-Permian boundary. A drop in CO2 levels and increase in arid conditions leads to change in woodland vegetation (Carboniferous rainforest collapse).	303.7 Template:Period start error
Kasimovian				307 Template:Period start error
Moscovian				315.2 Template:Period start error
Bashkirian				323.2 Template:Period start error*
Mississippian			Serpukhovian	Continents form a near circle around the opening Paleo-Tethys Ocean. Gondwana forms the southern to southwestern margin; Laurussia the west; Siberia, Amuria and Kazakhstania the north; North and South China the northeast; and, Annamia the eastern margin. The terranes collide with southeastern Laurussia during the Variscan orogeny. Antler orogeny continues, and opening of the Slide Mountain Ocean along western margin of Laurussia. Closure of Ural Ocean between Kazakhstania and Laurussia during the Ural orogeny. Development of Altai accretionary complexes along north and eastern margin of the Paleo-Tethys. Main phase of LPIA begins. Drop in global sea levels, extensive glaciation across Gondwana. Increasing atmospheric oxygen levels. Change from calcite to aragonite seas. Evolutionary radiations after the Late Devonian extinctions include brachiopods, bivalves, echinoderms, ammonoids, gastropods, sharks and ray-finned bony fish. Placoderms and graptolites die out. Proetida only group of trilobites. First freshwater mollusks and sharks. Arthropleura (millipede) largest ever terrestrial arthropod. First flying insects Paleodictyopora. Fish-like (Pederpes) and semi-aquatic tetrapods (Eucritta) appear on land. Seedless vascular plants and seed ferns diversify.	330.9 Template:Period start error
			Viséan		346.7 Template:Period start error*
			Tournaisian		358.9 Template:Period start error*
Devonian		Upper/Late	Famennian	Paleo-Tethys continues to open as the Armorican Terrane Assemblage (ATA) drifts north and Annamia-South China moves away from Gondwana. Rheic Ocean closes as ATA collides with Laurussia beginning the Variscan orogeny. Other orogenies: Antler, Ellesmerian, and Acadian (Laurussia); Achalian (Argentina); Tabberabberan/Lachlan (Australia); Ross (Antarctica); Kazakh (Kazakhstania). Period of high sea-levels, greenhouse conditions but decreasing atmospheric CO2 levels and slowly cooling climate with glaciations towards end. Vascular plants increase in size, develop large root systems and spread to upland areas. First forests, seed plants, and modern soil orders appear (alfisols and ultisols). Growth of massive reef systems. Major radiation of jawed fish with appearance of ray-finned, lobe-finned, and cartilaginous fish. Appearance of tetrapods (evolved from lobe-finned fish). Early amphibians move on to land. First ammonoids. Emplacement of the Viley and Pripyat–Dniepr–Donets large igneous provinces coincide with global marine anoxic events and the Kellwasser (c. 372 Ma) and Hangenberg (c. 359 Ma) mass extinctions. Kellwasser extinction: c. 20% of families and c. 50% of genera of marine invertebrates lost. Tabulate coral and stromatoporoid reef ecosystems wiped out. Loss of placoderms and many groups of jawless fish. Hangenberg extinction: loss of c. 16% of marine families and c. 21% of marine genera, including ammonoids, ostracods and sharks.	372.2 Template:Period start error*
			Frasnian		382.7 Template:Period start error*
		Middle	Givetian		387.7 Template:Period start error*
			Eifelian		393.3 Template:Period start error*
		Lower/Early	Emsian		407.6 Template:Period start error*
			Pragian		410.8 Template:Period start error*
			Lochkovian		419.2 Template:Period start error*
Silurian		Pridoli		Laurentia and Avalonia-Baltica collide as Iapetus Ocean closes, Caledonian-Scandian orogeny, and formation of Laurussia. Other orogenies: Salinic (Appalachians); Famatinian (South America) tapers off; Lachlan (Australia). Series of microcontinents and North China separate opening Paleo-Tethys and closing Paleoasian Ocean. Rheic Ocean widens between Gondwana and Laurussia. Siberia drifts north of equator. Temperatures increase as Hirnantian glaciation ends. Sea levels rise. Deposition of black shales, North Africa and Arabia, major hydrocarbon source rocks. Fluctuating climate with glacial advances results in changing ocean conditions causes extinction events, followed by ecological recoveries. Widespread evaporite deposition and hothouse climate by late Silurian. After end-Ordovician mass extinction, major radiation of graptolites, bivalves, gastropods, nautiloids, brachiopods, and crinoids. Increase in trilobites, but never fully recover. Corals and stromatoporiods diversify to produce large reefs. Proliferation of eurypterid arthropods. Earliest jawed fish (acanthodians). Appearance of ostracoderms. Appearance of vascular plants. First land animals including myriapods. First freshwater fish.	423 Template:Period start error*
		Ludlow	Ludfordian		425.6 Template:Period start error*
			Gorstian		427.4 Template:Period start error*
		Wenlock	Homerian		430.5 Template:Period start error*
			Sheinwoodian		433.4 Template:Period start error*
		Llandovery	Telychian		438.5 Template:Period start error*
			Aeronian		440.8 Template:Period start error*
			Rhuddanian		443.8 Template:Period start error*
Ordovician		Upper/Late	Hirnantian	Most continents lay in equatorial regions. Gondwana stretched to south pole. Panthalassic Ocean covered northern hemisphere. Avalonia rifted from Gondwana closing Iapetus Ocean in front, opening Rheic Ocean behind. South China close to Gondwana; North China between Siberia and Gondwana. Orogenies: Famatinian (South America); Benambran (Australia); Taconic (Laurentia). Baltica and Siberia drift north. Early greenhouse climate, cooling to icehouse conditions during Hirnantian Ice Age. Increase in atmospheric O2. Great Ordovician Biodiversification Event, major increase in new genera e.g. brachiopods, trilobites, corals, echinoderms, bryozoans, gastropods, bivalves, nautiloids, graptolites, and conodonts. Very high sea levels expand shallow continental seas, increase range of ecological niches. Modern marine ecosystems established. Earliest jawless fish. Tabulate corals and stromatoporoids dominant reef builders. Nautiloids main predators. Appearance of eurypterids and asteroids. Spread of early land plants. Late Ordovician mass extinction, loss of ~85 % of marine invertebrate species. Two pulses: first with onset of glaciation affects tropical fauna; second at end of ice age, warming climate impacts cool water species. Drastic reduction in trilobite, brachiopod, graptolite, echinoderm, conodont, coral, and chitinozoan genera.	445.2 Template:Period start error*
			Katian		453 Template:Period start error*
			Sandbian		458.4 Template:Period start error*
		Middle	Darriwilian		467.3 Template:Period start error*
			Dapingian		470 Template:Period start error*
		Lower/Early	Floian (formerly Arenig)		477.7 Template:Period start error*
			Tremadocian		485.4 Template:Period start error*
Cambrian		Furongian	Stage 10	Gondwana stretched from the south pole to equator, separated from Laurentia and Baltica by the Iapetus Ocean. Siberia lay close to the equator, north of Baltica; North and South China close to equatorial Gondwana. Orogenies: Cadomian (N.Africa/southern Europe); Kuunga (central Gondwana); Famatinian orogeny (South America); Delamerian (Australia). Greenhouse climate. High atmospheric CO2 levels. Atmospheric oxygen levels rose with increase in photosynthesising organisms. Early aragonite seas replaced by mixed aragonite-calcite seas with many animals developing CaCO3 skeletons. Rapid diversification of animals (Cambrian Explosion), most modern animal phyla appear, e.g. arthropods; molluscs; annelids; echinoderms; bryozoa; priapulids; brachiopods; hemichordates; and, chordates. Radiations of small shelly fossils. Giant anomalocarids (arthropods) dominant predators. Increase in bioturbation and grazing led to decline in stromatolites. Varying oxygen levels in oceans led to series of extinction events followed by radiations, including: earliest Cambrian loss of the Ediacaran acritarchs; end-Botomian extinction, linked to the Kalkarindji large igneous province eruptions (c. 514 Ma) with loss of archaeocyathids (early Cambrian reef builders) and hyoliths; and, end-Cambrian reduction in trilobite diversity. Many fossil lagerstätten, including Burgess Shale and Chengjiang Formation, formed by rapid burial in anoxic conditions.	~489.5
			Jiangshanian		~494 Template:Period start error*
			Paibian		~497 Template:Period start error*
		Miaolingian	Guzhangian		~500.5 Template:Period start error*
			Drumian		~504.5 Template:Period start error*
			Wuliuan		~509 Template:Period start error
		Series 2	Stage 4		~514 Template:Period start error
			Stage 3		~521 Template:Period start error
		Terreneuvian	Stage 2		~529 Template:Period start error
			Fortunian		541 Template:Period start error*
Proterozoic	Neoproterozoic	Ediacaran	As Rodinia breaks up Gondwana begins to assemble with the Pan-African (Africa and South America), East African (Africa, India and Arabia) and Kuungan (India, eastern Antarctica and western Australia) orogenies. Rapid rise in eukaryote diversity and numbers, including early animals. First biomineralising animals. First cnidarians (jellyfish and sea pens). 580 Ma Gaskiers glaciation, followed by rise in atmospheric oxygen levels. Ediacaran biota, deep water, soft-bodied organisms. First trace fossils including simple burrows and first evidence of bilateral symmetry.			~635 Template:Period start error*
		Cryogenian	Rodinia continues to breakup. 720 Ma eruptions of Franklin and Irkutsk LIPs mark rifting of Siberia from Laurentia. Iapetus Ocean begins to open as Amazonia and Baltica drift from Laurentia (from c. 650 Ma). Sturtian (720–658 Ma) and Marinoan (655–635 Ma) Snowball Earth glaciations.			~720 Template:Period start error
		Tonian	900 Ma Rodinia at its maximum extent. Intracontinental rifting begins c. 850 Ma, associated magmatism becoming widespread from 825 Ma, including the Malani Igneous Suite eruptions, India (c. 775 Ma). Beginning of breakup of Rodinia from c. 750 Ma.			1000 Template:Period start error
	Mesoproterozoic	Stenian	Collision between Laurentia and Amazonia results in Grenville orogeny which, with Sveconorwegian orogeny in Baltica, mark beginning of assembly of Rodinian supercontinent. Diversification of eukaryotes as oxygen levels increase. All major modern day clades, including Archaeplastida (e.g. red and green algae), Opisthokonta (e.g. fungi) and Amoebozoa appear. Evidence for life on land. Bangiomorpha pubescens (red algae) earliest known sexually reproducing organism.			1200 Template:Period start error
		Ectasian	Extensive dyke swarms found across all cratons mark completion of breakup of Columbia (Nuna) supercontinent. Oceans have oxygen-rich surface layers and euxinic (no oxygen, high levels of H2S) deep waters, leading to widespread formation of giant massive sulphide deposits (SEDEX) on the seafloor.			1400 Template:Period start error
		Calymmian	Columbia continues to fragment with widespread rift-related magmatism. Stromatolites reach their maximum extent and diversity as cyanobacteria diversify and flourish. Primitive seaweeds appear.			1600 Template:Period start error
	Paleoproterozoic	Statherian	Columbian supercontinent continues to grow along its margins by subduction-related magmatism and terrane accretion. Extension and rift zones begin to develop from c. 1.6 Ga. Eukaryotic red algae appear. Vredefort impact event (2.19 Ga).			1800 Template:Period start error
		Orosirian	2.0–1.8 Ga Columbia supercontinent assembles during collisional events including Trans-Hudson orogeny (North America), Limpopo Belt (South Africa), Capricorn orogeny (Australia) and Trans-North China orogeny. Drop in atmospheric oxygen as increased volcanism releases carbon dioxide. Grypania represents a possible early eukaryote. Sudbury Impact (1.85 Ga).			2050 Template:Period start error
		Rhyacian	Massive rise in atmospheric oxygen leads to expansion of life and increased burial of organic matter (Lomagundi carbon isotope excursion) (2.3 to 2.1 Ga). First red beds deposited. Eruptions of Bushveld Magmatic Province (from 2.25 Ga). Orogenies in South America and West Africa mark beginning of Columbia supercontinent. Yarrabubba impact structure (c. 2.23 Ga).			2300 Template:Period start error
		Siderian	2.5 – 2.42 Ga massive banded iron formations (BIFs) precipitated across most continents. Increasing atmospheric oxygen leads to Great Oxidation Event (c. 2.4––2.3 Ga) and Huronian glaciations as global temperatures drop.			2500 Template:Period start error
Archean	Neoarchean	Widespread mantle melting and crustal growth followed by formation of supercratons Superia (North America, northwest Europe, South Africa and northwest Australia) and Sclavia (Canada, Zimbabwe, southern India, southwestern Australia, Brazil and North China). Major diversification of cyanobacteria with multicellularity, increasing cell size and specialisation. Proliferation of oxygen-producing life leads to stepwise increase in atmospheric oxygen and deposition of banded iron formation.				2800 Template:Period start error
	Mesoarchean	Possible onset of plate tectonics c. 3 Ga. Cratons with low relief and extensive shallow marine environments. Weathering increased supply of nutrients to seas. Localised free oxygen associated with carbonate platform stromatolites. Evidence for oxygen-producing photosynthesisers (and possible eukaryotes) c. 3.2 Ga, and terrestrial life c. 3 Ga. Oldest evidence of glaciation c. 2.9 Ga.				3200 Template:Period start error
	Paleoarchean	Growth of cratons by terrane accretion. Oldest evidence for macroscopic life preserved as stromatolites (c. 3.4 Ga). Evidence for anaerobic prokaryotes in variety of environments including hydrothermal systems and within subsurface sediments. Microbial mats and biofilms become common in shallow water environments.				3600 Template:Period start error
	Eoarchean	Increasing formation of continental crust. 3.8 – 3.65 Ga chemical traces of life in earliest known sedimentary rocks (Isua Greenstone Belt). Anaerobic prokaryotes including chemotrophs and photosynthesisers appear from c. 3.7 Ga. Early BIFs due to anoxygenic photosynthesis.				4000 Template:Period start error
Hadean	Earth consolidates from solar nebula over 10-30 million years. Collision with Theia (proto-planet) forms Moon from debris. Core differentiates. Magma ocean cools, releasing CO2 and water to give CO2-rich atmosphere. Icy asteroids also contribute water. Mantle convection begins with rapid, shallow plate tectonics or stagnant lid tectonics. Decline in meteorite impacts with last ocean-vaporising impact c. 4.3 Ga. Probable emergence of life after this. Evidence for oldest crust from detrital zircon c. 4.37 Ga. Acasta gneiss complex contains oldest recorded rocks c. 4.03 Ga.					4600 Template:Period start error

Major proposed revisions to the ICC

Proposed Anthropocene Series/Epoch

Main article: Anthropocene

First suggested in 2000, the Anthropocene is a proposed epoch/series for the most recent time in Earth's history. While still informal, it is a widely used term to denote the present geologic time interval, in which many conditions and processes on Earth are profoundly altered by human impact. The definition of the Anthropocene as a geologic time period rather than a geologic event remains controversial and difficult.

In May 2019 the Anthropocene Working Group voted in favour of submitting a formal proposal to the ICS for the establishment of the Anthropocene Series/Epoch. The formal proposal was completed and submitted to the Subcommission on Quaternary Stratigraphy in late 2023 for a section in Crawford Lake, Ontario, with heightened Plutonium levels corresponding to 1952 CE. This proposal was rejected as a formal geologic epoch in early 2024, to be left instead as an "invaluable descriptor of human impact on the Earth system"

Proposals for revisions to pre-Cryogenian timeline

Shields et al. 2021

The ICS Subcommission for Cryogenian Stratigraphy has outlined a template to improve the pre-Cryogenian geologic time scale based on the rock record to bring it in line with the post-Tonian geologic time scale. This work assessed the geologic history of the currently defined eons and eras of the Precambrian, and the proposals in the "Geological Time Scale" books 2004, 2012, and 2020. Their recommend revisions of the pre-Cryogenian geologic time scale were as below (changes from the current scale [v2023/09] are italicised). This suggestion was unanimously rejected by the International Subcommission for Precambrian Stratigraphy, based on scientific weaknesses.

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

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

ICC pre-Cambrian timeline (v2024/12, current as of January 2025), shown to scale:

Van Kranendonk et al. 2012 (GTS2012)

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

• Hadean Eon (4567–4030 Ma)
  • Chaotian Era/Erathem (4567–4404 Ma) – the name alluding both to the mythological Chaos and the chaotic phase of planet formation.
  • Jack Hillsian or Zirconian Era/Erathem (4404–4030 Ma) – both names allude to the Jack Hills Greenstone Belt which provided the oldest mineral grains on Earth, zircons.
• Archean Eon/Eonothem (4030–2420 Ma)
  • Paleoarchean Era/Erathem (4030–3490 Ma)
    • Acastan Period/System (4030–3810 Ma) – named after the Acasta Gneiss, one of the oldest preserved pieces of continental crust.
    • Isuan Period/System (3810–3490 Ma) – named after the Isua Greenstone Belt.
  • Mesoarchean Era/Erathem (3490–2780 Ma)
    • Vaalbaran Period/System (3490–3020 Ma) – based on the names of the Kaapvaal (Southern Africa) and Pilbara (Western Australia) cratons, to reflect the growth of stable continental nuclei or proto-cratonic kernels.
    • Pongolan Period/System (3020–2780 Ma) – named after the Pongola Supergroup, in reference to the well preserved evidence of terrestrial microbial communities in those rocks.
  • Neoarchean Era/Erathem (2780–2420 Ma)
    • Methanian Period/System (2780–2630 Ma) – named for the inferred predominance of methanotrophic prokaryotes
    • Siderian Period/System (2630–2420 Ma) – named for the voluminous banded iron formations formed within its duration.
• Proterozoic Eon/Eonothem (2420–538.8 Ma)
  • Paleoproterozoic Era/Erathem (2420–1780 Ma)
    • Oxygenian Period/System (2420–2250 Ma) – named for displaying the first evidence for a global oxidising atmosphere.
    • Jatulian or Eukaryian Period/System (2250–2060 Ma) – names are respectively for the Lomagundi–Jatuli δ¹³C isotopic excursion event spanning its duration, and for the (proposed) first fossil appearance of eukaryotes.
    • Columbian Period/System (2060–1780 Ma) – named after the supercontinent Columbia.
  • Mesoproterozoic Era/Erathem (1780–850 Ma)
    • Rodinian Period/System (1780–850 Ma) – named after the supercontinent Rodinia, stable environment.

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

ICC pre-Cambrian timeline (v2024/12, current as of January 2025), shown to scale:

Extraterrestrial geologic time scales

Main articles: Lunar geologic timescale, Martian geologic timescale, and Geology of Venus

Some other planets and satellites 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 giant planets, 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.

Lunar (selenological) time scale

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

Martian geologic time scale

The geological history of Mars has been divided into two alternate time scales. The first time scale for Mars was developed by studying the impact crater densities on the Martian surface. Through this method four periods have been defined, the Pre-Noachian (~4,500–4,100 Ma), Noachian (~4,100–3,700 Ma), Hesperian (~3,700–3,000 Ma), and Amazonian (~3,000 Ma to present). Template:Mars timescale A second time scale based on mineral alteration observed by the OMEGA spectrometer on board the Mars Express. Using this method, three periods were defined, the Phyllocian (~4,500–4,000 Ma), Theiikian (~4,000–3,500 Ma), and Siderikian (~3,500 Ma to present).

See also

• Cosmic calendar
• Deep time
• Evolutionary history of life
• Formation and evolution of the Solar System
• Geology of Mars
• Geon (geology)
• History of Earth
• History of geology
• History of paleontology
• List of geochronologic names
• Natural history
• New Zealand geologic time scale
• Prehistoric life
• Timeline of the Big Bang
• Timeline of evolution
• Timeline of the geologic history of the United States
• Timeline of human evolution
• Timeline of natural history
• Timeline of paleontology

Further reading

• Aubry, Marie-Pierre; Van Couvering, John A.; Christie-Blick, Nicholas; Landing, Ed; Pratt, Brian R.; Owen, Donald E.; Ferrusquia-Villafranca, Ismael (2009). "Terminology of geological time: Establishment of a community standard". Stratigraphy. 6 (2): 100–105. doi:10.7916/D8DR35JQ.
• Gradstein, Felix M.; Ogg, James G. (June 2004). "Geologic Time Scale 2004 – why, how, and where next!". Lethaia. 37 (2): 175–181. Bibcode:2004Letha..37..175G. doi:10.1080/00241160410006483.
• Gradstein, Felix M.; Ogg, James G.; Smith, Alan G., eds. (2005). A Geologic Time Scale 2004. doi:10.1017/CBO9780511536045. ISBN 978-0-521-78673-7.
• Gradstein, Felix M.; Ogg, James G.; Smith, Alan G.; Bleeker, Wouter; Laurens, Lucas, J. (June 2004). "A new Geologic Time Scale, with special reference to Precambrian and Neogene". Episodes. 27 (2): 83–100. doi:10.18814/epiiugs/2004/v27i2/002. Template:CORE output.
• Ialenti, Vincent (28 September 2014). "Embracing 'Deep Time' Thinking". NPR. NPR Cosmos & Culture.
• Ialenti, Vincent (21 September 2014). "Pondering 'Deep Time' Could Inspire New Ways To View Climate Change". NPR. NPR Cosmos & Culture.
• Knoll, Andrew H.; Walter, Malcolm R.; Narbonne, Guy M.; Christie-Blick, Nicholas (30 July 2004). "A New Period for the Geologic Time Scale". Science. 305 (5684): 621–622. doi:10.1126/science.1098803. PMID 15286353.
• Levin, Harold L. (2010). [[[:Template:GBurl]] "Time and Geology"]. The Earth Through Time. Hoboken, New Jersey: John Wiley & Sons. ISBN 978-0-470-38774-0.
• Montenari, Michael, ed. (2016). Stratigraphy & Timescales. Academic Press. ISBN 978-0-12-811550-3.
• Montenari, Michael (2017). Advances in Sequence Stratigraphy (1st ed.). Amsterdam: Academic Press (Elsevier). ISBN 978-0-12-813077-3.
• Montenari, Michael, ed. (2018). Cyclostratigraphy and Astrochronology (1st ed.). Amsterdam: Academic Press (Elsevier). ISBN 978-0-12-815098-6.
• Montenari, Michael, ed. (2019). Case Studies in Isotope Stratigraphy (1st ed.). Amsterdam: Academic Press (Elsevier). ISBN 978-0-12-817552-1.
• Montenari, Michael, ed. (2020). Carbon Isotope Stratigraphy (1st ed.). Amsterdam: Academic Press (Elsevier). ISBN 978-0-12-820991-2.
• Montenari, Michael, ed. (2021). Calcareous Nannofossil Biostratigraphy (1st ed.). Amsterdam: Academic Press (Elsevier). ISBN 978-0-12-824624-5.
• Montenari, Michael, ed. (2022). Integrated Quaternary Stratigraphy (1st ed.). Amsterdam: Academic Press (Elsevier). ISBN 978-0-323-98913-8.
• Montenari, Michael, ed. (2023). Stratigraphy of Geo- and Biodynamic Processes (1st ed.). Amsterdam: Academic Press (Elsevier). ISBN 978-0-323-99242-8.
• Nichols, Gary (2013). Sedimentology and Stratigraphy. John Wiley & Sons. ISBN 978-1-118-68777-2.
• Williams, Aiden (2019). Sedimentology and Stratigraphy. Callisto Reference. ISBN 978-1-64116-075-9.

External links

• The current version of the International Chronostratigraphic Chart can be found at stratigraphy.org/chart
• Interactive version of the International Chronostratigraphic Chart is found at stratigraphy.org/timescale
• A list of current Global Boundary Stratotype and Section Points is found at stratigraphy.org/gssps
• NASA: Geologic Time (archived 18 April 2005)
• GSA: Geologic Time Scale (archived 20 January 2019)
• British Geological Survey: Geological Timechart
• GeoWhen Database (archived 23 June 2004)
• National Museum of Natural History – Geologic Time (archived 11 November 2005)
• SeeGrid: Geological Time Systems. Archived 23 July 2008 at the Wayback Machine. Information model for the geologic time scale.
• Exploring Time from Planck Time to the lifespan of the universe
• Lane, Alfred C, and Marble, John Putman 1937. Report of the Committee on the measurement of geologic time
• Lessons for Children on Geologic Time (archived 14 July 2011)
• Deep Time – A History of the Earth : Interactive Infographic
• Geology Buzz: Geologic Time Scale. Archived 12 August 2021 at the Wayback Machine.