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The geologic time scale, or geological time scale, (GTS) is a representation of
time Time is the continued sequence of existence and events that occurs in an apparently irreversible succession from the past, through the present, into the future. It is a component quantity of various measurements used to sequence events, t ...
based on the rock record of
Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surf ...
. It is a system of
chronological dating Chronological dating, or simply dating, is the process of attributing to an object or event a date in the past, allowing such object or event to be located in a previously established chronology. This usually requires what is commonly known as a "d ...
that uses
chronostratigraphy Chronostratigraphy is the branch of stratigraphy that studies the ages of rock strata in relation to time. The ultimate aim of chronostratigraphy is to arrange the sequence of deposition and the time of deposition of all rocks within a geologica ...
(the process of relating
strata In geology and related fields, a stratum ( : strata) is a layer of rock or sediment characterized by certain lithologic properties or attributes that distinguish it from adjacent layers from which it is separated by visible surfaces known as e ...
to time) and geochronology (scientific branch of
geology Geology () is a branch of natural science concerned with Earth and other astronomical objects, the features or rocks of which it is composed, and the processes by which they change over time. Modern geology significantly overlaps all other Ea ...
that aims to determine the age of rocks). It is used primarily by Earth scientists (including
geologist A geologist is a scientist who studies the solid, liquid, and gaseous matter that constitutes Earth and other terrestrial planets, as well as the processes that shape them. Geologists usually study geology, earth science, or geophysics, alt ...
s, paleontologists,
geophysicists Geophysics () is a subject of natural science concerned with the physical processes and physical properties of the Earth and its surrounding space environment, and the use of quantitative methods for their analysis. The term ''geophysics'' so ...
, geochemists, and
paleoclimatologists Paleoclimatology (British spelling, palaeoclimatology) is the study of climates for which direct measurements were not taken. As instrumental records only span a tiny part of Earth's history, the reconstruction of ancient climate is important to ...
) 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 Paleomagnetism (or palaeomagnetismsee ), is the study of magnetic fields recorded in rocks, sediment, or archeological materials. Geophysicists who specialize in paleomagnetism are called ''paleomagnetists.'' Certain magnetic minerals in rocks ...
properties, and
fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...
s. The definition of standardized international units of geologic time is the responsibility of the
International Commission on Stratigraphy The International Commission on Stratigraphy (ICS), sometimes referred to unofficially as the "International Stratigraphic Commission", is a daughter or major subcommittee grade scientific daughter organization that concerns itself with stratigr ...
(ICS), a constituent body of the
International Union of Geological Sciences The International Union of Geological Sciences (IUGS) is an international non-governmental organization devoted to international cooperation in the field of geology. About The IUGS was founded in 1961 and is a Scientific Union member of the Inte ...
(IUGS), whose primary objective is to precisely define global chronostratigraphic units of the International Chronostratigraphic Chart (ICC) that are used to define divisions of geologic time. The chronostratigraphic divisions are in turn used to define geochronologic units. While some regional terms are still in use, the table of geologic time presented in this article conforms to the
nomenclature Nomenclature (, ) is a system of names or terms, or the rules for forming these terms in a particular field of arts or sciences. The principles of naming vary from the relatively informal conventions of everyday speech to the internationally agre ...
, ages, and color codes set forth by the ICS as this is the standard, reference global geologic time scale – the International Geological Time Scale.


Principles

The geologic time scale is a way of representing
deep time Deep time is a term introduced and applied by John McPhee to the concept of geologic time in his book ''Basin and Range'' (1981), parts of which originally appeared in the '' New Yorker'' magazine. The philosophical concept of geological time ...
based on events that have occurred throughout Earth's history, a time span of about 4.54 ± 0.05 Ga (4.54 billion years). It chronologically organizes strata, and subsequently time, by observing fundamental changes in stratigraphy that correspond to major geological or paleontological events. For example, the
Cretaceous–Paleogene extinction event The Cretaceous–Paleogene (K–Pg) extinction event (also known as the Cretaceous–Tertiary extinction) was a sudden extinction event, mass extinction of three-quarters of the plant and animal species on Earth, approximately 66 million y ...
, marks the lower boundary of the
Paleogene The Paleogene ( ; also spelled Palaeogene or Palæogene; informally Lower Tertiary or Early Tertiary) is a geologic period and system that spans 43 million years from the end of the Cretaceous Period million years ago (Mya) to the beginning of ...
System/Period and thus the boundary between the
Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...
and Paleogene Systems/Periods. For divisions prior to the Cryogenian, arbitrary numeric boundary definitions ( Global Standard Stratigraphic Ages, GSSAs) are used to divide geologic time. Proposals have been made to better reconcile these divisions with the rock record. Historically, regional geologic time scales were 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 standardizing globally significant and identifiable stratigraphic horizons that can be used to define the lower boundaries of chronostratigraphic units. Defining chronostratigraphic units in such a manner allows for the use of global, standardised nomenclature. The ICC represents this ongoing effort. The relative relationships of rocks for determining their chronostratigraphic positions use the overriding principles of: * Superposition – Newer rock beds will lie on top of older rock beds unless the succession has been overturned. *
Horizontality ''Horizontalidad'' (, horizontality or horizontalism) is a social relationship that advocates the creation, development, and maintenance of social structures for the equitable distribution of management power. These structures and relationships ...
– All rock layers were originally deposited horizontally. * Lateral continuity – Originally deposited layers of rock extend laterally in all directions until either thinning out or being cut off by a different rock layer. * Biologic succession (where applicable) – This states that each stratum in a succession contains a distinctive set of fossils. This allows for correlation of stratum even when the horizon between them is not continuous. *
Cross-cutting relationships Cross-cutting relationships is a principle of geology that states that the geologic feature which cuts another is the younger of the two features. It is a relative dating technique in geology. It was first developed by Danish geological pioneer ...
– A rock feature that cuts across another feature must be younger than the rock it cuts. * Inclusion – Small fragments of one type of rock but embedded in a second type of rock must have formed first, and were included when the second rock was forming. * Relationships of unconformities – Geologic features representing periods of erosion or non-deposition, indicating non-continuous sediment deposition.


Terminology

The GTS is divided into chronostratigraphic units and their corresponding geochronologic units. These are represented on the ICC published by the ICS; however, regional terms are still in use in some areas. is the element of
stratigraphy Stratigraphy is a branch of geology concerned with the study of rock layers ( strata) and layering (stratification). It is primarily used in the study of sedimentary and layered volcanic rocks. Stratigraphy has three related subfields: lithost ...
that deals with the relation between rock bodies and the relative measurement of geological time. It is the process where distinct strata between defined stratigraphic horizons are assigned to represent a relative interval of geologic time. A is a body of rock, layered or unlayered, that is defined between specified stratigraphic horizons which represent specified intervals of geologic time. They include all rocks representative of a specific interval of geologic time, and only this time span. Eonothem, erathem, system, series, subseries, stage, and substage are the hierarchical chronostratigraphic units. is the scientific branch of geology that aims to determine the age of rocks, fossils, and sediments either through absolute (e.g.,
radiometric dating Radiometric dating, radioactive dating or radioisotope dating is a technique which is used to date materials such as rocks or carbon, in which trace radioactive impurities were selectively incorporated when they were formed. The method compares t ...
) or relative means (e.g., stratigraphic position,
Paleomagnetism Paleomagnetism (or palaeomagnetismsee ), is the study of magnetic fields recorded in rocks, sediment, or archeological materials. Geophysicists who specialize in paleomagnetism are called ''paleomagnetists.'' Certain magnetic minerals in roc ...
, stable isotope ratios). A is a subdivision of geologic time. It is a numeric representation of an intangible property (time). Eon, era, period, epoch, subepoch, age, and subage are the hierarchical geochronologic units. is the field of geochronology that numerically quantifies geologic time. A (GSSP) is an internationally agreed upon reference point on a stratigraphic section which defines the lower boundaries of stages on the geologic time scale. (Recently this has been used to define the base of a system) A (GSSA) is a numeric only, chronologic reference point used to define the base of geochronologic units prior to the Cryogenian. These points are arbitrarily defined. They are used where GSSPs have not yet been established. Research is ongoing to define GSSPs for the base of all units that are currently defined by GSSAs. The numeric (geochronometric) representation of a geochronologic unit can, and is more frequently subject to, change when geochronology refines the geochronometry, while the equivalent chronostratigraphic unit remains the same, and their revision is less common. For example, in early 2022 the boundary between the
Ediacaran The Ediacaran Period ( ) is a geological period that spans 96 million years from the end of the Cryogenian Period 635 million years ago (Mya), to the beginning of the Cambrian Period 538.8 Mya. It marks the end of the Proterozoic Eon, and t ...
and
Cambrian The Cambrian Period ( ; sometimes symbolized Ꞓ) was the first geological period of the Paleozoic Era, and of the Phanerozoic Eon. The Cambrian lasted 53.4 million years from the end of the preceding Ediacaran Period 538.8 million years ag ...
Periods (geochronologic units) was revised from 541 Ma to 538.8 Ma but the rock definition of the boundary (GSSP) at the base of the Cambrian, and thus the boundary between the Ediacaran and Cambrian Systems (chronostratigraphic units) has not changed, merely the geochronometry has been refined. The numeric values on the ICC are represented by the unit Ma (megaannum) meaning "million
year A year or annus is the orbital period of a planetary body, for example, the Earth, moving in its orbit around the Sun. Due to the Earth's axial tilt, the course of a year sees the passing of the seasons, marked by change in weather, the ...
s", i.e., Ma, the lower boundary of the
Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The J ...
Period, is defined as 201,300,000 years old with an uncertainty of 200,000 years. Other
SI prefix The International System of Units, known by the international abbreviation SI in all languages and sometimes pleonastically as the SI system, is the modern form of the metric system and the world's most widely used system of measurement. ...
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 Before Present (BP) years, or "years before present", is a time scale used mainly in archaeology, geology and other scientific disciplines to specify when events occurred relative to the origin of practical radiocarbon dating in the 1950s. Becaus ...
).


Divisions of geologic time

An is the largest (formal) geochronologic time unit and is the equivalent of a chronostratigraphic
eonothem In stratigraphy and geology, an eonothem is the totality of rock strata laid down in the stratigraphic record deposited during a certain eon of the continuous geologic timescale. The eonothem is not to be confused with the eon itself, which is ...
. there are three formally defined eons/eonothems: the
Archean The Archean Eon ( , also spelled Archaean or Archæan) is the second of four eon (geology), geologic eons of History of Earth, Earth's history, representing the time from . The Archean was preceded by the Hadean Eon and followed by the Proterozo ...
,
Proterozoic The Proterozoic () is a geological eon spanning the time interval from 2500 to 538.8million years ago. It is the most recent part of the Precambrian "supereon". It is also the longest eon of the Earth's geologic time scale, and it is subdivided ...
, and
Phanerozoic The Phanerozoic Eon is the current geologic eon in the geologic time scale, and the one during which abundant animal and plant life has existed. It covers 538.8 million years to the present, and it began with the Cambrian Period, when anima ...
. The
Hadean The Hadean ( ) is a geologic eon of Earth history preceding the Archean. On Earth, the Hadean began with the planet's formation about 4.54 billion years ago (although the start of the Hadean is defined as the age of the oldest solid material ...
is an informal eon/eonothem, but is commonly used. An is the second largest geochronologic time unit and is the equivalent of a chronostratigraphic erathem. there are currently ten defined eras/erathems. A is a major rank below an ''era'' and above an ''epoch''. It is the geochronologic equivalent of a chronostratigraphic system. there are currently 22 defined periods/systems. As an exception two subperiods/subsystems are used for the Carboniferous Period/System. An is the second smallest geochronologic unit, between a ''period'' and an ''age''. It is the equivalent of a chronostratigraphic series. there are currently 37 defined and one informal ''epochs/series''. There are also 11 subepochs/subseries which are all within the
Neogene The Neogene ( ), informally Upper Tertiary or Late Tertiary, is a geologic period and system that spans 20.45 million years from the end of the Paleogene Period million years ago (Mya) to the beginning of the present Quaternary Period Mya. ...
and Quaternary. The use of subseries/subepochs as formal ranks/units in international chronostratigraphy was ratified in 2022. An is the smallest hierarchical geochronologic unit and is the equivalent of a chronostratigraphic stage. there are currently 96 formal and five informal ''ages/stages''. A is a non-hierarchical formal geochronology unit of unspecified rank and is the equivalent of a chronostratigraphic chronozone. These correlate with
magnetostratigraphic Magnetostratigraphy is a geophysical correlation technique used to date sedimentary and volcanic sequences. The method works by collecting oriented samples at measured intervals throughout the section. The samples are analyzed to determine their ' ...
,
lithostratigraphic Lithostratigraphy is a sub-discipline of stratigraphy, the geological science associated with the study of strata or rock layers. Major focuses include geochronology, comparative geology, and petrology. In general, strata are primarily igneous ...
, or biostratigraphic units as they are based on previously defined stratigraphic units or geologic features. The and subdivisions are used as the geochronologic equivalents of the chronostratigraphic and , e.g., Early
Triassic The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago (Mya), to the beginning of the Jurassic Period 201.36 Mya. The Triassic is the first and shortest period ...
Period (geochronologic unit) is used in place of Lower Triassic Series (chronostratigraphic unit). In essence, it is true to say that rocks representing a given chronostratigraphic unit are that chronostratigraphic unit, and the time they were laid down in is the geochronologic unit, i.e., the rocks that represent the
Silurian The Silurian ( ) is a geologic period and system spanning 24.6 million years from the end of the Ordovician Period, at million years ago (Mya), to the beginning of the Devonian Period, Mya. The Silurian is the shortest period of the Paleozoi ...
Series the Silurian Series and they were deposited the Silurian Period.


Naming of geologic time

The names of geologic time units are defined for chronostratigraphic units with the corresponding geochronologic unit sharing the same name with a change to the latter (e.g. Phanerozoic
Eonothem In stratigraphy and geology, an eonothem is the totality of rock strata laid down in the stratigraphic record deposited during a certain eon of the continuous geologic timescale. The eonothem is not to be confused with the eon itself, which is ...
becomes the Phanerozoic Eon). Names of erathems in the Phanerozoic were chosen to reflect major changes of the history of life on Earth:
Paleozoic The Paleozoic (or Palaeozoic) Era is the earliest of three geologic eras of the Phanerozoic Eon. The name ''Paleozoic'' ( ;) was coined by the British geologist Adam Sedgwick in 1838 by combining the Greek words ''palaiós'' (, "old") and ' ...
(old life),
Mesozoic The Mesozoic Era ( ), also called the Age of Reptiles, the Age of Conifers, and colloquially as the Age of the Dinosaurs is the second-to-last era of Earth's geological history, lasting from about , comprising the Triassic, Jurassic and Creta ...
(middle life), and
Cenozoic The Cenozoic ( ; ) is Earth's current geological era, representing the last 66million years of Earth's history. It is characterised by the dominance of mammals, birds and flowering plants, a cooling and drying climate, and the current configu ...
(new life). Names of systems are diverse in origin, with some indicating chronologic position (e.g., Paleogene), while others are named for
lithology The lithology of a rock unit is a description of its physical characteristics visible at outcrop, in hand or core samples, or with low magnification microscopy. Physical characteristics include colour, texture, grain size, and composition. Li ...
(e.g., Cretaceous),
geography Geography (from Greek: , ''geographia''. Combination of Greek words ‘Geo’ (The Earth) and ‘Graphien’ (to describe), literally "earth description") is a field of science devoted to the study of the lands, features, inhabitants, a ...
(e.g.,
Permian The Permian ( ) is a geologic period and stratigraphic system which spans 47 million years from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.9 Mya. It is the last period of the Pale ...
), or are tribal (e.g.,
Ordovician The Ordovician ( ) is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start of the Silurian Period Mya. ...
) in origin. Most currently recognised series and subseries are named for their position within a system/series (early/middle/late); however, the ICS advocates for all new series and subseries to be named for a geographic feature in the vicinity of its stratotype or
type locality Type locality may refer to: * Type locality (biology) * Type locality (geology) See also * Local (disambiguation) * Locality (disambiguation) {{disambiguation ...
. 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 The Precambrian (or Pre-Cambrian, sometimes abbreviated pꞒ, 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 th ...
or pre-Cambrian (Supereon). }, the god of the underworld (the hell, the inferno) in the Greek mythology.


History of the geologic time scale


Early history

While a modern geological time scale was not formulated until 1911 by Arthur Holmes, the broader concept that rocks and time are related can be traced back to (at least) the philosophers of
Ancient Greece Ancient Greece ( el, Ἑλλάς, Hellás) was a northeastern Mediterranean civilization, existing from the Greek Dark Ages of the 12th–9th centuries BC to the end of classical antiquity ( AD 600), that comprised a loose collection of cult ...
.
Xenophanes of Colophon Xenophanes of Colophon (; grc, Ξενοφάνης ὁ Κολοφώνιος ; c. 570 – c. 478 BC) was a Greek philosopher, theologian, poet, and critic of Homer from Ionia who travelled throughout the Greek-speaking world in early Classical A ...
(c. 570–487  BCE) observed rock beds with fossils of shells located above the sea-level, viewed them as once living organisms, and used this to imply an unstable relationship in which the sea had at times transgressed over the land and at other times had regressed. This view was shared by a few of Xenophanes' contemporaries and those that followed, including
Aristotle Aristotle (; grc-gre, Ἀριστοτέλης ''Aristotélēs'', ; 384–322 BC) was a Greek philosopher and polymath during the Classical Greece, Classical period in Ancient Greece. Taught by Plato, he was the founder of the Peripatet ...
(384–322 BCE) who (with additional observations) reasoned that the positions of land and sea had changed over long periods of time. The concept of
deep time Deep time is a term introduced and applied by John McPhee to the concept of geologic time in his book ''Basin and Range'' (1981), parts of which originally appeared in the '' New Yorker'' magazine. The philosophical concept of geological time ...
was also recognised by Chinese naturalist
Shen Kuo Shen Kuo (; 1031–1095) or Shen Gua, courtesy name Cunzhong (存中) and pseudonym Mengqi (now usually given as Mengxi) Weng (夢溪翁),Yao (2003), 544. was a Chinese polymathic scientist and statesman of the Song dynasty (960–1279). She ...
(1031–1095) and Islamic
scientist A scientist is a person who conducts scientific research to advance knowledge in an area of the natural sciences. In classical antiquity, there was no real ancient analog of a modern scientist. Instead, philosophers engaged in the philosophica ...
-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 A polymath ( el, πολυμαθής, , "having learned much"; la, homo universalis, "universal human") is an individual whose knowledge spans a substantial number of subjects, known to draw on complex bodies of knowledge to solve specific pro ...
Avicenna Ibn Sina ( fa, ابن سینا; 980 – June 1037 CE), commonly known in the West as Avicenna (), was a Persian polymath who is regarded as one of the most significant physicians, astronomers, philosophers, and writers of the Islam ...
(Ibn Sînâ, 980–1037) who wrote in ''
The Book of Healing ''The Book of Healing'' (; ; also known as ) is a scientific and philosophical encyclopedia written by Abu Ali ibn Sīna (aka Avicenna) from medieval Persia, near Bukhara in Maverounnahr. He most likely began to compose the book in 1014, comp ...
'' (1027) on the concept of stratification and superposition, pre-dating Nicolas Steno by more than six centuries. Avicenna also recognised fossils as "petrifications of the bodies of plants and animals", with the 13th-century Dominican
bishop A bishop is an ordained clergy member who is entrusted with a position of authority and oversight in a religious institution. In Christianity, bishops are normally responsible for the governance of dioceses. The role or office of bishop is ...
Albertus Magnus Albertus Magnus (c. 1200 – 15 November 1280), also known as Saint Albert the Great or Albert of Cologne, was a German Dominican friar, philosopher, scientist, and bishop. Later canonised as a Catholic saint, he was known during his li ...
(c. 1200–1280) extending this into a theory of a petrifying fluid. These works appeared to have little influence on
scholar A scholar is a person who pursues academic and intellectual activities, particularly academics who apply their intellectualism into expertise in an area of study. A scholar can also be an academic, who works as a professor, teacher, or research ...
s in
Medieval Europe In the history of Europe, the Middle Ages or medieval period lasted approximately from the late 5th to the late 15th centuries, similar to the post-classical period of global history. It began with the fall of the Western Roman Empire a ...
who looked to the
Bible The Bible (from Koine Greek , , 'the books') is a collection of religious texts or scriptures that are held to be sacred in Christianity, Judaism, Samaritanism, and many other religions. The Bible is an anthologya compilation of texts o ...
to explain the origins of fossils and sea-level changes, often attributing these to the '
Deluge A deluge is a large downpour of rain, often a flood. The Deluge refers to the flood narrative in the Biblical book of Genesis. Deluge may also refer to: History *Deluge (history), the Swedish and Russian invasion of the Polish-Lithuanian Comm ...
', including
Ristoro d'Arezzo Ristoro or Restoro d'Arezzo was an Italian monk and scientist of the Middle Ages. Italian scholar Enrico Narducci calls him the ' Humboldt' of the thirteenth century. Life and works Restoro was born in Arezzo, Tuscany, at an unknown date in the ...
in 1282. It was not until the
Italian Renaissance The Italian Renaissance ( it, Rinascimento ) was a period in Italian history covering the 15th and 16th centuries. The period is known for the initial development of the broader Renaissance culture that spread across Europe and marked the tra ...
when
Leonardo da Vinci Leonardo di ser Piero da Vinci (15 April 14522 May 1519) was an Italian polymath of the High Renaissance who was active as a painter, Drawing, draughtsman, engineer, scientist, theorist, sculptor, and architect. While his fame initially re ...
(1452–1519) would reinvigorate the relationships between stratification, relative sea-level change, and time, denouncing attribution of fossils to the 'Deluge': 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 Genesis may refer to: Bible * Book of Genesis, the first book of the biblical scriptures of both Judaism and Christianity, describing the creation of the Earth and of mankind * Genesis creation narrative, the first several chapters of the Book o ...
were not readily accepted and dissent from
religious Religion is usually defined as a social- cultural system of designated behaviors and practices, morals, beliefs, worldviews, texts, sanctified places, prophecies, ethics, or organizations, that generally relates humanity to supernatural, ...
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.


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 Creation may refer to: Religion *'' Creatio ex nihilo'', the concept that matter was created by God out of nothing *Creation myth, a religious story of the origin of the world and how people first came to inhabit it *Creationism, the belief that ...
). 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 correlation of strata relative 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 by
Thomas Burnet Thomas Burnet (c. 1635? – 27 September 1715) was an English theologian and writer on cosmogony. Life He was born at Croft near Darlington in 1635. After studying at Northallerton Grammar School under Thomas Smelt, he went to Clare College ...
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"''. This attribution to the 'Deluge', while questioned earlier by the likes of da Vinci, was the foundation of Abraham Gottlob Werner's (1749–1817) Neptunism theory in which all rocks precipitated out of a single flood. A competing theory,
Plutonism Plutonism is the geologic theory that the igneous rocks forming the Earth originated from intrusive magmatic activity, with a continuing gradual process of weathering and erosion wearing away rocks, which were then deposited on the sea bed, r ...
, was developed by Anton Moro (1687–1784) and also used primary and secondary divisions for rock units. In this early version of the Plutonism theory, the interior of Earth was seen as hot, and this drove the creation of primary igneous and metamorphic rocks and secondary rocks formed contorted and fossiliferous sediments. These primary and secondary divisions were expanded on 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 Neputism 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 James Hutton (; 3 June O.S.172614 June 1726 New Style. – 26 March 1797) was a Scottish geologist, agriculturalist, chemical manufacturer, naturalist and physician. Often referred to as the father of modern geology, he played a key role ...
(1726–1797), in particular his '' Theory of the Earth'', first presented before the
Royal Society of Edinburgh The Royal Society of Edinburgh is Scotland's national academy of science and letters. It is a registered charity that operates on a wholly independent and non-partisan basis and provides public benefit throughout Scotland. It was established i ...
in 1785. Hutton's theory would later become known as
uniformitarianism Uniformitarianism, also known as the Doctrine of Uniformity or the Uniformitarian Principle, is the assumption that the same natural laws and processes that operate in our present-day scientific observations have always operated in the universe in ...
, popularised by
John Playfair John Playfair FRSE, FRS (10 March 1748 – 20 July 1819) was a Church of Scotland minister, remembered as a scientist and mathematician, and a professor of natural philosophy at the University of Edinburgh. He is best known for his book ''Illu ...
(1748–1819) and later
Charles Lyell Sir Charles Lyell, 1st Baronet, (14 November 1797 – 22 February 1875) was a Scottish geologist who demonstrated the power of known natural causes in explaining the earth's history. He is best known as the author of '' Principles of Geol ...
(1797–1875) in his ''
Principles of Geology ''Principles of Geology: Being an Attempt to Explain the Former Changes of the Earth's Surface, by Reference to Causes Now in Operation'' is a book by the Scottish geologist Charles Lyell that was first published in 3 volumes from 1830–1833. L ...
''. Their theories strongly contested the 6,000 year age of the Earth as suggested determined by
James Ussher James Ussher (or Usher; 4 January 1581 – 21 March 1656) was the Church of Ireland Archbishop of Armagh and Primate of All Ireland between 1625 and 1656. He was a prolific scholar and church leader, who today is most famous for his iden ...
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 Léopold Nicolas Frédéric, Baron Cuvier (; 23 August 1769 – 13 May 1832), known as Georges Cuvier, was a French naturalist and zoologist, sometimes referred to as the "founding father of paleontology". Cuvier was a major figure in na ...
,
Jean d'Omalius d'Halloy Jean Baptiste Julien d'Omalius d'Halloy (17 February 1783 in Liège – 15 January 1875 in Brussels) was a Belgian geologist. He also wrote on races. Early life and education Born in Liège, he was the only son of an ancient and noble family ...
, and
Alexandre Brongniart Alexandre Brongniart (5 February 17707 October 1847) was a French chemist, mineralogist, geologist, paleontologist, and zoologist, who collaborated with Georges Cuvier on a study of the geology of the region around Paris. Observing fossil conten ...
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

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 Thermodynamics is a branch of physics that deals with heat, work, and temperature, and their relation to energy, entropy, and the physical properties of matter and radiation. The behavior of these quantities is governed by the four laws o ...
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 William Thomson, 1st Baron Kelvin, (26 June 182417 December 1907) was a British mathematician, mathematical physicist and engineer born in Belfast. Professor of Natural Philosophy at the University of Glasgow for 53 years, he did important ...
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 Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration, or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is consid ...
by
Henri Becquerel Antoine Henri Becquerel (; 15 December 1852 – 25 August 1908) was a French engineer, physicist, Nobel laureate, and the first person to discover evidence of radioactivity. For work in this field he, along with Marie Skłodowska-Curie and Pi ...
,
Marie Curie Marie Salomea Skłodowska–Curie ( , , ; born Maria Salomea Skłodowska, ; 7 November 1867 – 4 July 1934) was a Polish and naturalized-French physicist and chemist who conducted pioneering research on radioactivity. She was the first ...
, and
Pierre Curie Pierre Curie ( , ; 15 May 1859 – 19 April 1906) was a French physicist, a pioneer in crystallography, magnetism, piezoelectricity, and radioactivity. In 1903, he received the Nobel Prize in Physics with his wife, Marie Curie, and Henri Becq ...
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 Ernest Rutherford, 1st Baron Rutherford of Nelson, (30 August 1871 – 19 October 1937) was a New Zealand physicist who came to be known as the father of nuclear physics. ''Encyclopædia Britannica'' considers him to be the greatest ...
,
Bertram Boltwood Bertram Borden Boltwood (July 27, 1870 Amherst, Massachusetts – August 15, 1927, Hancock Point, Maine) was an American pioneer of radiochemistry. Boltwood attended Yale University, became a professor there and in 1910 was appointed chair of th ...
, 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
isotope Isotopes are two or more types of atoms that have the same atomic number (number of protons in their nuclei) and position in the periodic table (and hence belong to the same chemical element), and that differ in nucleon numbers ( mass number ...
s in 1913 by
Frederick Soddy Frederick Soddy FRS (2 September 1877 – 22 September 1956) was an English radiochemist who explained, with Ernest Rutherford, that radioactivity is due to the transmutation of elements, now known to involve nuclear reactions. He also pro ...
, and the developments in
mass spectrometry Mass spectrometry (MS) is an analytical technique that is used to measure the mass-to-charge ratio of ions. The results are presented as a '' mass spectrum'', a plot of intensity as a function of the mass-to-charge ratio. Mass spectrometry is u ...
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 geologic 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.


Major proposed revisions to the ICC


Proposed Anthropocene Series/Epoch

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 Anthropocene has not been ratified by the ICS; however, in May 2019 the
Anthropocene Working Group The Anthropocene Working Group (AWG) is an interdisciplinary research group dedicated to the study of the Anthropocene as a geological time unit. It was established in 2009 as part of the Subcommission on Quaternary Stratigraphy (SQS), a constituent ...
voted in favour of submitting a formal proposal to the ICS for the establishment of the Anthropocene Series/Epoch. Nevertheless, the definition of the Anthropocene as a geologic time period rather than a geologic event remains controversial and difficult.


Proposals for revisions to pre-Cryogenian timeline


Shields et al. 2021

An international working group of the ICS on pre-Cryogenian chronostratigraphic subdivision have outlined a template to improve the pre-Cyrogenian geologic time scale based on the rock record to bring it in line with the post-Tonian geologic time scale. This work assessed the geologic history of the currently defined eons and eras of the pre-Cambrian, and the proposals in the "Geological Time Scale" books ''2004,'' ''2012,'' and ''2020.'' Their recommend revisions of the pre-Cryogenian geologic time scale were (changes from the current scale 2022/02are italicised): * Three divisions of the Archean instead of four by dropping Eoarchean, and revisions to their geochronometric definition, along with the repositioning of the Siderian into the latest Neoarchean, and a potential Kratian division in the Neoarchean. ** Archean (4000–''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 word ''κράτος'' (krátos), meaning 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 the Greek word σκουριά (''skouriá''), meaning '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 the Greek words κλείσιμο (''kleísimo'') meaning 'closure', and σύνδεση (''sýndesi'') meaning '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: ImageSize = width:1300 height:100 PlotArea = left:80 right:20 bottom:20 top:5 AlignBars = justify Colors = id:proterozoic value:rgb(0.968,0.207,0.388) id:neoproterozoic value:rgb(0.996,0.701,0.258) id:ediacaran value:rgb(0.996,0.85,0.415) id:cryogenian value:rgb(0.996,0.8,0.36) id:tonian value:rgb(0.996,0.75,0.305) id:kleisian value:rgb(0.996,0.773,0.431) id:mesoproterozoic value:rgb(0.996,0.705,0.384) id:stenian value:rgb(0.996,0.85,0.604) id:ectasian value:rgb(0.996,0.8,0.541) id:calymmian value:rgb(0.996,0.75,0.478) id:paleoproterozoic value:rgb(0.968,0.263,0.44) id:skourian value:rgb(0.949,0.439,0.545) id:statherian value:rgb(0.968,0.459,0.655) id:orosirian value:rgb(0.968,0.408,0.596) id:rhyacian value:rgb(0.968,0.357,0.537) id:archean value:rgb(0.996,0.157,0.498) id:neoarchean value:rgb(0.976,0.608,0.757) id:mesoarchean value:rgb(0.968,0.408,0.662) id:paleoarchean value:rgb(0.96,0.266,0.624) id:hadean value:rgb(0.717,0,0.494) id:black value:black id:white value:white Period = from:-4600 till:-538.8 TimeAxis = orientation:horizontal ScaleMajor = unit:year increment:500 start:-4500 ScaleMinor = unit:year increment:100 start:-4500 PlotData = align:center textcolor:black fontsize:8 mark:(line,black) width:25 shift:(0,-5) bar:Eonothem/Eon from: -2450 till: -538.8 text:Proterozoic color:proterozoic from: -4000 till: -2450 text:Archean color:archean from: start till: -4000 text:Hadean color:hadean bar:Erathem/Era from: -1000 till: -538.8 text:Neoproterozoic color:neoproterozoic from: -1800 till: -1000 text:Mesoproterozoic color:mesoproterozoic from: -2450 till: -1800 text:Paleoproterozoic color:paleoproterozoic from: -3000 till: -2450 text:Neoarchean color:neoarchean from: -3300 till: -3000 text:Mesoarchean color:mesoarchean from: -4000 till: -3300 text:Paleoarchean color:paleoarchean from: start till: -4000 color:white bar:System/Period fontsize:7 from: -635 till: -538.8 text:Ed. color:ediacaran from: -720 till: -635 text:Cr. color:cryogenian from: -800 till: -720 text:Tonian color:tonian from: -1000 till: -800 text:?kleisian color:kleisian from: -1200 till: -1000 text:Stenian color:stenian from: -1400 till: -1200 text:Ectasian color:ectasian from: -1600 till: -1400 text:Calymmian color:calymmian from: -1800 till: -1600 text:Statherian color:statherian from: -2050 till: -1800 text:Orosirian color:orosirian from: -2300 till: -2050 text:Rhyacian color:rhyacian from: -2450 till: -2300 text:?Skourian color:skourian from: -2700 till: -2450 text:Siderian color:neoarchean from: -3000 till: -2700 text:?Kratian color:neoarchean from: start till: -3000 color:white Current ICC pre-Cambrian timeline (v2022/02), shown to scale: ImageSize = width:1300 height:100 PlotArea = left:80 right:20 bottom:20 top:5 AlignBars = justify Colors = id:proterozoic value:rgb(0.968,0.207,0.388) id:neoproterozoic value:rgb(0.996,0.701,0.258) id:ediacaran value:rgb(0.996,0.85,0.415) id:cryogenian value:rgb(0.996,0.8,0.36) id:tonian value:rgb(0.996,0.75,0.305) id:mesoproterozoic value:rgb(0.996,0.705,0.384) id:stenian value:rgb(0.996,0.85,0.604) id:ectasian value:rgb(0.996,0.8,0.541) id:calymmian value:rgb(0.996,0.75,0.478) id:paleoproterozoic value:rgb(0.968,0.263,0.44) id:statherian value:rgb(0.968,0.459,0.655) id:orosirian value:rgb(0.968,0.408,0.596) id:rhyacian value:rgb(0.968,0.357,0.537) id:siderian value:rgb(0.968,0.306,0.478) id:archean value:rgb(0.996,0.157,0.498) id:neoarchean value:rgb(0.976,0.608,0.757) id:mesoarchean value:rgb(0.968,0.408,0.662) id:paleoarchean value:rgb(0.96,0.266,0.624) id:eoarchean value:rgb(0.902,0.114,0.549) id:hadean value:rgb(0.717,0,0.494) id:black value:black id:white value:white Period = from:-4600 till:-538.8 TimeAxis = orientation:horizontal ScaleMajor = unit:year increment:500 start:-4500 ScaleMinor = unit:year increment:100 start:-4500 PlotData = align:center textcolor:black fontsize:8 mark:(line,black) width:25 shift:(0,-5) bar:Eonothem/Eon from: -2500 till: -538.8 text:Proterozoic color:proterozoic from: -4000 till: -2500 text:Archean color:archean from: start till: -4000 text:Hadean color:hadean bar:Erathem/Era from: -1000 till: -538.8 text:Neoproterozoic color:neoproterozoic from: -1600 till: -1000 text:Mesoproterozoic color:mesoproterozoic from: -2500 till: -1600 text:Paleoproterozoic color:paleoproterozoic from: -2800 till: -2500 text:Neoarchean color:neoarchean from: -3200 till: -2800 text:Mesoarchean color:mesoarchean from: -3600 till: -3200 text:Paleoarchean color:paleoarchean from: -4000 till: -3600 text:Eoarchean color:eoarchean from: start till: -4000 color:white bar:Sytem/Period fontsize:7 from: -635 till: -538.8 text:Ed. color:ediacaran from: -720 till: -635 text:Cr. color:cryogenian from: -1000 till: -720 text:Tonian color:tonian from: -1200 till: -1000 text:Stenian color:stenian from: -1400 till: -1200 text:Ectasian color:ectasian from: -1600 till: -1400 text:Calymmian color:calymmian from: -1800 till: -1600 text:Statherian color:statherian from: -2050 till: -1800 text:Orosirian color:orosirian from: -2300 till: -2050 text:Rhyacian color:rhyacian from: -2500 till: -2300 text:Siderian color:siderian from: start till: -2500 color:white


Van Kranendonk et al. 2012 (GTS2012)

The book, ''Geologic Time Scale 2012,'' was the last commercial publication of an international chronostratigraphic chart that was closely associated with the ICS. It included a proposal to substantially revise the pre-Cryogenian time scale to reflect important events such as the formation of the solar system and the
Great Oxidation Event The Great Oxidation Event (GOE), also called the Great Oxygenation Event, the Oxygen Catastrophe, the Oxygen Revolution, the Oxygen Crisis, or the Oxygen Holocaust, was a time interval during the Paleoproterozoic era when the Earth's atmospher ...
, among others, while at the same time maintaining most of the previous chronostratigraphic nomenclature for the pertinent time span. these proposed changes have not been accepted by the ICS. The proposed changes were (changes from the current scale 2022/02are italicised): * Hadean Eon (''4567–4030'' Ma) ** Chaotian Era/Erathem (4567–4404 Ma) – the name alluding both to the mythological Chaos and the
chaotic Chaotic was originally a Danish trading card game. It expanded to an online game in America which then became a television program based on the game. The program was able to be seen on 4Kids TV (Fox affiliates, nationwide), Jetix, The CW4Kids ...
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,
zircon Zircon () is a mineral belonging to the group of nesosilicates and is a source of the metal zirconium. Its chemical name is zirconium(IV) silicate, and its corresponding chemical formula is Zr SiO4. An empirical formula showing some of th ...
s. * 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 Continental crust is the layer of igneous, sedimentary, and metamorphic rocks that forms the geological continents and the areas of shallow seabed close to their shores, known as continental shelves. This layer is sometimes called '' sial' ...
. *** ''Isuan'' Period (3''810–3490'' 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 Kapvaal (Southern Africa) and
Pilbara The Pilbara () is a large, dry, thinly populated region in the north of Western Australia. It is known for its Aboriginal peoples; its ancient landscapes; the red earth; and its vast mineral deposits, in particular iron ore. It is also a gl ...
(Western Australia)
craton A craton (, , or ; from grc-gre, κράτος "strength") is an old and stable part of the continental lithosphere, which consists of Earth's two topmost layers, the crust and the uppermost mantle. Having often survived cycles of merging and ...
s, to reflect the growth of stable continental nuclei or proto-
craton A craton (, , or ; from grc-gre, κράτος "strength") is an old and stable part of the continental lithosphere, which consists of Earth's two topmost layers, the crust and the uppermost mantle. Having often survived cycles of merging and ...
ic 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 Methanotrophs (sometimes called methanophiles) are prokaryotes that metabolize methane as their source of carbon and chemical energy. They are bacteria or archaea, can grow aerobically or anaerobically, and require single-carbon compounds to su ...
prokaryotes A prokaryote () is a single-celled organism that lacks a nucleus and other membrane-bound organelles. The word ''prokaryote'' comes from the Greek πρό (, 'before') and κάρυον (, 'nut' or 'kernel').Campbell, N. "Biology:Concepts & Conn ...
*** Siderian Period/System (''2630–2420'' Ma) – named for the voluminous
banded iron formation Banded iron formations (also known as banded ironstone formations or BIFs) are distinctive units of sedimentary rock consisting of alternating layers of iron oxides and iron-poor chert. They can be up to several hundred meters in thickness a ...
s 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 oxidizing 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 Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the three domains of life. Bact ...
. *** ''Columbian Period/System'' (''2060–1780'' Ma) – named after the
supercontinent In geology, a supercontinent is the assembly of most or all of Earth's continental blocks or cratons to form a single large landmass. However, some geologists use a different definition, "a grouping of formerly dispersed continents", which lea ...
Columbia Columbia may refer to: * Columbia (personification), the historical female national personification of the United States, and a poetic name for America Places North America Natural features * Columbia Plateau, a geologic and geographic region in ...
. ** 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: ImageSize = width:1200 height:100 PlotArea = left:80 right:20 bottom:20 top:5 AlignBars = justify Colors = id:proterozoic value:rgb(0.968,0.207,0.388) id:neoproterozoic value:rgb(0.996,0.701,0.258) id:ediacaran value:rgb(0.996,0.85,0.415) id:cryogenian value:rgb(0.996,0.8,0.36) id:tonian value:rgb(0.996,0.75,0.305) id:mesoproterozoic value:rgb(0.996,0.705,0.384) id:rodinian value:rgb(0.996,0.75,0.478) id:paleoproterozoic value:rgb(0.968,0.263,0.44) id:columbian value:rgb(0.968,0.459,0.655) id:eukaryian value:rgb(0.968,0.408,0.596) id:oxygenian value:rgb(0.968,0.357,0.537) id:archean value:rgb(0.996,0.157,0.498) id:neoarchean value:rgb(0.976,0.608,0.757) id:siderian value:rgb(0.976,0.7,0.85) id:methanian value:rgb(0.976,0.65,0.8) id:mesoarchean value:rgb(0.968,0.408,0.662) id:pongolan value:rgb(0.968,0.5,0.75) id:vaalbaran value:rgb(0.968,0.45,0.7) id:paleoarchean value:rgb(0.96,0.266,0.624) id:isuan value:rgb(0.96,0.35,0.65) id:acastan value:rgb(0.96,0.3,0.6) id:hadean value:rgb(0.717,0,0.494) id:zirconian value:rgb(0.902,0.114,0.549) id:chaotian value:rgb(0.8,0.05,0.5) id:black value:black id:white value:white Period = from:-4600 till:-538.8 TimeAxis = orientation:horizontal ScaleMajor = unit:year increment:500 start:-4500 ScaleMinor = unit:year increment:100 start:-4500 PlotData = align:center textcolor:black fontsize:8 mark:(line,black) width:25 shift:(0,-5) bar:Eonothem/Eon from: -2420 till: -538.8 text:Proterozoic color:proterozoic from: -4030 till: -2420 text:Archean color:archean from: -4567 till: -4030 text:Hadean color:hadean from: start till: -4567 color:white bar:Erathem/Era from: -850 till: -538.8 text:Neoproterozoic color:neoproterozoic from: -1780 till: -850 text:Mesoproterozoic color:mesoproterozoic from: -2420 till: -1780 text:Paleoproterozoic color:paleoproterozoic from: -2780 till: -2420 text:Neoarchean color:neoarchean from: -3490 till: -2780 text:Mesoarchean color:mesoarchean from: -4030 till: -3490 text:Paleoarchean color:paleoarchean from: -4404 till: -4030 text:Zirconian color:zirconian from: -4567 till: -4404 text:Chaotian color:chaotian from: start till: -4567 color:white bar:System/Period fontsize:7 from: -630 till: -538.8 text:Ed. color:ediacaran from: -850 till: -630 text:Cr. color:cryogenian from: -1780 till: -850 text:Rodinian color:rodinian from: -2060 till: -1780 text:Columbian color:columbian from: -2250 till: -2060 text:Eukaryian color:eukaryian from: -2420 till: -2250 text:Oxygenian color:oxygenian from: -2630 till: -2420 text:Siderian color:siderian from: -2780 till: -2630 text:Methanian color:methanian from: -3020 till: -2780 text:Pongolan color:pongolan from: -3490 till: -3020 text:Vaalbaran color:vaalbaran from: -3810 till: -3490 text:Isuan color:isuan from: -4030 till: -3810 text:Acastan color:acastan from: start till: -4030 color:white Current ICC pre-Cambrian timeline (v2022/02), shown to scale: ImageSize = width:1200 height:100 PlotArea = left:80 right:20 bottom:20 top:5 AlignBars = justify Colors = id:proterozoic value:rgb(0.968,0.207,0.388) id:neoproterozoic value:rgb(0.996,0.701,0.258) id:ediacaran value:rgb(0.996,0.85,0.415) id:cryogenian value:rgb(0.996,0.8,0.36) id:tonian value:rgb(0.996,0.75,0.305) id:mesoproterozoic value:rgb(0.996,0.705,0.384) id:stenian value:rgb(0.996,0.85,0.604) id:ectasian value:rgb(0.996,0.8,0.541) id:calymmian value:rgb(0.996,0.75,0.478) id:paleoproterozoic value:rgb(0.968,0.263,0.44) id:statherian value:rgb(0.968,0.459,0.655) id:orosirian value:rgb(0.968,0.408,0.596) id:rhyacian value:rgb(0.968,0.357,0.537) id:siderian value:rgb(0.968,0.306,0.478) id:archean value:rgb(0.996,0.157,0.498) id:neoarchean value:rgb(0.976,0.608,0.757) id:mesoarchean value:rgb(0.968,0.408,0.662) id:paleoarchean value:rgb(0.96,0.266,0.624) id:eoarchean value:rgb(0.902,0.114,0.549) id:hadean value:rgb(0.717,0,0.494) id:black value:black id:white value:white Period = from:-4600 till:-538.8 TimeAxis = orientation:horizontal ScaleMajor = unit:year increment:500 start:-4500 ScaleMinor = unit:year increment:100 start:-4500 PlotData = align:center textcolor:black fontsize:8 mark:(line,black) width:25 shift:(0,-5) bar:Eonothem/Eon from: -2500 till: -538.8 text:Proterozoic color:proterozoic from: -4000 till: -2500 text:Archean color:archean from: start till: -4000 text:Hadean color:hadean bar:Erathem/Era from: -1000 till: -538.8 text:Neoproterozoic color:neoproterozoic from: -1600 till: -1000 text:Mesoproterozoic color:mesoproterozoic from: -2500 till: -1600 text:Paleoproterozoic color:paleoproterozoic from: -2800 till: -2500 text:Neoarchean color:neoarchean from: -3200 till: -2800 text:Mesoarchean color:mesoarchean from: -3600 till: -3200 text:Paleoarchean color:paleoarchean from: -4000 till: -3600 text:Eoarchean color:eoarchean from: start till: -4000 color:white bar:System/Period fontsize:7 from: -635 till: -538.8 text:Ed. color:ediacaran from: -720 till: -635 text:Cr. color:cryogenian from: -1000 till: -720 text:Tonian color:tonian from: -1200 till: -1000 text:Stenian color:stenian from: -1400 till: -1200 text:Ectasian color:ectasian from: -1600 till: -1400 text:Calymmian color:calymmian from: -1800 till: -1600 text:Statherian color:statherian from: -2050 till: -1800 text:Orosirian color:orosirian from: -2300 till: -2050 text:Rhyacian color:rhyacian from: -2500 till: -2300 text:Siderian color:siderian from: start till: -2500 color:white


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 The Phanerozoic Eon is the current geologic eon in the geologic time scale, and the one during which abundant animal and plant life has existed. It covers 538.8 million years to the present, and it began with the Cambrian Period, when anima ...
Eon looks longer than the rest, it merely spans ~539 million years (~12% of Earth's history), whilst the previous three eons collectively span ~3,461 million years (~76% of Earth's history). This bias toward the most recent eon is in part due to the relative lack of information about events that occurred during the first three eons compared to the current eon (the Phanerozoic). The use of subseries/subepochs has been ratified by the ICS. The content of the table is based on the official ICC produced and maintained by the ICS who also provide an online interactive version of this chart. The interactive version is based on a service delivering a machine-readable
Resource Description Framework The Resource Description Framework (RDF) is a World Wide Web Consortium (W3C) standard originally designed as a data model for metadata. It has come to be used as a general method for description and exchange of graph data. RDF provides a variety of ...
/
Web Ontology Language The Web Ontology Language (OWL) is a family of knowledge representation languages for authoring ontologies. Ontologies are a formal way to describe taxonomies and classification networks, essentially defining the structure of knowledge for vario ...
representation of the time scale, which is available through the Commission for the Management and Application of Geoscience Information GeoSciML project as a service and at a SPARQL end-point.


Non-Earth based geologic time scales

Some other
planets A planet is a large, rounded astronomical body that is neither a star nor its remnant. The best available theory of planet formation is the nebular hypothesis, which posits that an interstellar cloud collapses out of a nebula to create a young ...
and
satellites A satellite or artificial satellite is an object intentionally placed into orbit in outer space. Except for passive satellites, most satellites have an electricity generation system for equipment on board, such as solar panels or radioisotop ...
in the
Solar System The Solar System Capitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar ...
have sufficiently rigid structures to have preserved records of their own histories, for example,
Venus Venus is the second planet from the Sun. It is sometimes called Earth's "sister" or "twin" planet as it is almost as large and has a similar composition. As an interior planet to Earth, Venus (like Mercury) appears in Earth's sky never f ...
,
Mars Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury. In the English language, Mars is named for the Roman god of war. Mars is a terrestrial planet with a thin atmos ...
and the Earth's
Moon The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width ...
. Dominantly fluid planets, such as the
gas giant A gas giant is a giant planet composed mainly of hydrogen and helium. Gas giants are also called failed stars because they contain the same basic elements as a star. Jupiter and Saturn are the gas giants of the Solar System. The term "gas giant" ...
s, 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 crater An impact crater is a circular depression in the surface of a solid astronomical object formed by the hypervelocity impact of a smaller object. In contrast to volcanic craters, which result from explosion or internal collapse, impact crater ...
ing,
volcanism Volcanism, vulcanism or volcanicity is the phenomenon of eruption of molten rock (magma) onto the Earth#Surface, surface of the Earth or a solid-surface planet or moon, where lava, pyroclastics, and volcanic gases erupt through a break in the su ...
, and
erosion Erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust, and then transports it to another location where it is deposited. Erosion is di ...
. 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 that is the only other body which we have rock samples with a known geological context.


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). A second time scale based on mineral alteration observed by the OMEGA
spectrometer A spectrometer () is a scientific instrument used to separate and measure spectral components of a physical phenomenon. Spectrometer is a broad term often used to describe instruments that measure a continuous variable of a phenomenon where th ...
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). ImageSize = width:800 height:50 PlotArea = left:15 right:15 bottom:20 top:5 AlignBars = early Period = from:-4500 till:0 TimeAxis = orientation:horizontal ScaleMajor = unit:year increment:500 start:-4500 ScaleMinor = unit:year increment:100 start:-4500 Colors = id:sidericol value:rgb(1,0.4,0.3) id:theiicol value:rgb(1,0.2,0.5) id:phyllocol value:rgb(0.7,0.4,1) PlotData= align:center textcolor:black fontsize:8 mark:(line,black) width:25 shift:(0,-5) text:Siderikan from:-3500 till:0 color:sidericol text:Theiikian from:-4000 till:-3500 color:theiicol text:Phyllocian from:start till:-4000 color:phyllocol


See also

*
Age of the Earth The age of Earth is estimated to be 4.54 ± 0.05 billion years This age may represent the age of Earth's accretion, or core formation, or of the material from which Earth formed. This dating is based on evidence from radiometric age-dating of ...
*
Cosmic calendar The Cosmic Calendar is a method to visualize the chronology of the universe, scaling its currently understood age of 13.8 billion years to a single year in order to help intuit it for pedagogical purposes in science education or popular science. ...
*
Deep time Deep time is a term introduced and applied by John McPhee to the concept of geologic time in his book ''Basin and Range'' (1981), parts of which originally appeared in the '' New Yorker'' magazine. The philosophical concept of geological time ...
*
Evolutionary history of life The history of life on Earth traces the processes by which living and fossil organisms evolved, from the earliest emergence of life to present day. Earth formed about 4.5 billion years ago (abbreviated as ''Ga'', for '' gigaannum'') and evid ...
*
Formation and evolution of the Solar System The formation of the Solar System began about 4.6 billion years ago with the gravitational collapse of a small part of a giant molecular cloud. Most of the collapsing mass collected in the center, forming the Sun, while the rest flattened int ...
* Geological history of Earth *
Geology of Mars The geology of Mars is the scientific study of the surface, crust, and interior of the planet Mars. It emphasizes the composition, structure, history, and physical processes that shape the planet. It is analogous to the field of terrestrial geo ...
* Geon (geology) *
Graphical timeline of the universe This more than 20-billion-year timeline of our universe shows the best estimates of major events from the universe's beginning to anticipated future events. Zero on the scale is the present day. A large step on the scale is one billion years; a s ...
* History of the Earth *
History of geology The history of geology is concerned with the development of the natural science of geology. Geology is the scientific study of the origin, history, and structure of Earth. Antiquity Some of the first geological thoughts were about the ori ...
* History of paleontology *
List of fossil sites This list of fossil sites is a worldwide list of localities known well for the presence of fossils. Some entries in this list are notable for a single, unique find, while others are notable for the large number of fossils found there. Many of t ...
* List of geochronologic names *
Logarithmic timeline A logarithmic timeline is a timeline laid out according to a logarithmic scale. This necessarily implies a zero point and an infinity point, neither of which can be displayed. The most natural zero point is the Big Bang, looking forward, but ...
*
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 o ...
* Martian geologic timescale * Natural history *
New 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 systems of dividing geologic time into epochs and faunal stages. In New Zealand, these epo ...
* Prehistoric life *
Timeline of the Big Bang The chronology of the universe describes the history and future of the universe according to Big Bang cosmology. Research published in 2015 estimates the earliest stages of the universe's existence as taking place 13.8 billion years ago, wit ...
*
Timeline of evolution The timeline of the evolutionary history of life represents the current scientific theory outlining the major events during the development of life on planet Earth. Dates in this article are consensus estimates based on scientific evidence, ma ...
* Timeline of the geologic history of the United States * Timeline of human evolution * Timeline of natural history *
Timeline of paleontology Timeline of paleontology Antiquity – 16th century * 6th century B.C. — The pre-Socratic Greek philosopher Xenophanes of Colophon argues that fossils of marine organisms show that dry land was once under water. * 4th century B.C.  ...


Notes


References


Further reading

* * * * * * * * * * * * * * * Nichols, Gary (2013).
Sedimentology and Stratigraphy
' (2nd ed.). Hoboken: Wiley-Blackwell. * Williams, Aiden (2019).
Sedimentology and Stratigraphy
' (1st ed.). Forest Hills, NY: Callisto Reference.


External links

* The current version of the International Chronostratigraphic Chart can be found a
stratigraphy.org/chart
* Interactive version of the International Chronostratigraphic Chart is found a
stratigraphy.org/timescale
* A list of current Global Boundary Stratotype and Section Points is found a
stratigraphy.org/gssps



GSA: Geologic Time Scale



GeoWhen Database



SeeGrid: Geological Time Systems
Information model for the geologic time scale
Exploring Time
from Planck Time to the lifespan of the universe
Episodes
Gradstein, Felix M. et al. (2004) ''A new Geologic Time Scale, with special reference to Precambrian and Neogene'', Episodes, Vol. 27, no. 2 June 2004 (pdf) * Lane, Alfred C, and Marble, John Putman 1937
Report of the Committee on the measurement of geologic time



Deep Time – A History of the Earth : Interactive InfographicGeology Buzz: Geologic Time Scale
{{Authority control + Evolution-related timelines Geochronology Timescale Articles which contain graphical timelines International Commission on Stratigraphy geologic time scale of Earth