geologic time scale
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The geologic time scale or geological time scale (GTS) is a representation of
time Time is the continuous progression of existence that occurs in an apparently irreversible process, irreversible succession from the past, through the present, and into the future. It is a component quantity of various measurements used to sequ ...
based on the rock record of
Earth Earth is the third planet from the Sun and the only astronomical object known to Planetary habitability, harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all ...
. It is a system of chronological dating that uses chronostratigraphy (the process of relating strata to time) and geochronology (a scientific branch of
geology Geology (). is a branch of natural science concerned with the Earth and other astronomical objects, the rocks of which they are composed, and the processes by which they change over time. Modern geology significantly overlaps all other Earth ...
that aims to determine the age of rocks). 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
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 preserve ...
s. The definition of standardised international units of geological time is the responsibility of the
International Commission on Stratigraphy The International Commission on Stratigraphy (ICS), sometimes unofficially referred to as the International Stratigraphic Commission, is a daughter or major subcommittee grade scientific organization that concerns itself with stratigraphy, strati ...
(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) that are used to define divisions of geological time. The chronostratigraphic divisions are in turn used to define geochronologic units.


Principles

The geologic time scale is a way of representing deep time based on events that have occurred through Earth's history, a time span of about 4.54 ± 0.05 billion years. It chronologically organises 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, marks the lower boundary of the Paleogene System/Period and thus the boundary between the
Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...
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 standardising 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 International Chronostratigraphic Chart represents this ongoing effort. Several key principles are used to determine the relative relationships of rocks and thus their chronostratigraphic position. 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.


Divisions of geologic time

The geologic time scale is divided into chronostratigraphic units and their corresponding geochronologic units. * An is the largest geochronologic time unit and is equivalent to a chronostratigraphic eonothem. There are four formally defined eons: the Hadean,
Archean The Archean ( , also spelled Archaean or Archæan), in older sources sometimes called the Archaeozoic, is the second of the four geologic eons of Earth's history of Earth, history, preceded by the Hadean Eon and followed by the Proterozoic and t ...
, Proterozoic and Phanerozoic. * An 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 The Mesoproterozoic Era is a geologic era that occurred from . The Mesoproterozoic was the first era of Earth's history for which a fairly definitive geological record survives. Continents existed during the preceding era (the Paleoproterozoic ...
,
Neoproterozoic The Neoproterozoic Era is the last of the three geologic eras of the Proterozoic geologic eon, eon, spanning from 1 billion to 538.8 million years ago, and is the last era of the Precambrian "supereon". It is preceded by the Mesoproterozoic era an ...
, Paleozoic,
Mesozoic The Mesozoic Era is the Era (geology), era of Earth's Geologic time scale, geological history, lasting from about , comprising the Triassic, Jurassic and Cretaceous Period (geology), Periods. It is characterized by the dominance of archosaurian r ...
and Cenozoic, with none from the Hadean eon. * A is equivalent to a chronostratigraphic
system A system is a group of interacting or interrelated elements that act according to a set of rules to form a unified whole. A system, surrounded and influenced by its open system (systems theory), environment, is described by its boundaries, str ...
. There are 22 defined periods, with the current being the Quaternary period. As an exception, two subperiods are used for the Carboniferous Period. * An 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 The Holocene () is the current geologic time scale, geological epoch, beginning approximately 11,700 years ago. It follows the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene to ...
. 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 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 ' 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. The subdivisions and are used as the geochronologic equivalents of the chronostratigraphic and , e.g., Early
Triassic The Triassic ( ; sometimes symbolized 🝈) is a geologic period and system which spans 50.5 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.4 Mya. The Triassic is t ...
Period (geochronologic unit) is used in place of Lower Triassic System (chronostratigraphic unit). Rocks representing a given chronostratigraphic unit are that chronostratigraphic unit, and the time they were laid down in is the geochronologic unit, e.g., the rocks that represent the Silurian System the Silurian System and they were deposited the Silurian Period. This definition means the numeric age of a geochronologic unit can be changed (and is more often subject to change) when refined by geochronometry while the equivalent chronostratigraphic unit (the revision of which is less frequent) remains unchanged. For example, in early 2022, the boundary between the
Ediacaran The Ediacaran ( ) is a geological period of the Neoproterozoic geologic era, Era that spans 96 million years from the end of the Cryogenian Period at 635 Million years ago, Mya to the beginning of the Cambrian Period at 538.8 Mya. It is the last ...
and Cambrian 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 been changed; rather, the absolute age has merely been refined.


Terminology

is the element of stratigraphy 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. A is a subdivision of geologic time. It is a numeric representation of an intangible property (time). These units are arranged in a hierarchy: eon, era, period, epoch, subepoch, age, and subage. is the scientific branch of geology that aims to determine the age of rocks, fossils, and sediments either through absolute (e.g., radiometric dating) or relative means (e.g., stratigraphic position, paleomagnetism, stable isotope ratios). is the field of geochronology that numerically quantifies geologic time. A (GSSP) is an internationally agreed-upon reference point on a stratigraphic section that 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 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 Chronostratigrahpic Chart are represented by the unit Ma (megaannum, for 'million years'). For example, 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 143.1 Mya. ...
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).


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 The Mesozoic Era is the Era (geology), era of Earth's Geologic time scale, geological history, lasting from about , comprising the Triassic, Jurassic and Cretaceous Period (geology), Periods. It is characterized by the dominance of archosaurian r ...
(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 Geography (from Ancient Greek ; combining 'Earth' and 'write', literally 'Earth writing') is the study of the lands, features, inhabitants, and phenomena of Earth. Geography is an all-encompassing discipline that seeks an understanding o ...
(e.g.,
Permian The Permian ( ) is a geologic period and System (stratigraphy), 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 251.902 Mya. It is the s ...
), 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


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
philosopher Philosophy ('love of wisdom' in Ancient Greek) is a systematic study of general and fundamental questions concerning topics like existence, reason, knowledge, Value (ethics and social sciences), value, mind, and language. It is a rational an ...
s of
Ancient Greece Ancient Greece () was a northeastern Mediterranean civilization, existing from the Greek Dark Ages of the 12th–9th centuries BC to the end of classical antiquity (), that comprised a loose collection of culturally and linguistically r ...
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 Aristotle (; 384–322 BC) was an Ancient Greek philosophy, Ancient Greek philosopher and polymath. His writings cover a broad range of subjects spanning the natural sciences, philosophy, linguistics, economics, politics, psychology, a ...
(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
Islam Islam is an Abrahamic religions, Abrahamic monotheistic religion based on the Quran, and the teachings of Muhammad. Adherents of Islam are called Muslims, who are estimated to number Islam by country, 2 billion worldwide and are the world ...
ic
scientist A scientist is a person who Scientific method, researches to advance knowledge in an Branches of science, area of the natural sciences. In classical antiquity, there was no real ancient analog of a modern scientist. Instead, philosophers engag ...
-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 or polyhistor is an individual whose knowledge spans many different subjects, known to draw on complex bodies of knowledge to solve specific problems. Polymaths often prefer a specific context in which to explain their knowledge, ...
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 A bishop is an ordained member of the clergy who is entrusted with a position of Episcopal polity, authority and oversight in a religious institution. In Christianity, bishops are normally responsible for the governance and administration of di ...
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 In the history of Europe, the Middle Ages or medieval period lasted approximately from the 5th to the late 15th centuries, similarly to the post-classical period of World history (field), global history. It began with the fall of the West ...
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 Leonardo di ser Piero da Vinci (15 April 1452 - 2 May 1519) was an Italian polymath of the High Renaissance who was active as a painter, draughtsman, engineer, scientist, theorist, sculptor, and architect. While his fame initially rested o ...
(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 were not readily accepted and dissent from
religious Religion is a range of social- cultural systems, including designated behaviors and practices, morals, beliefs, worldviews, texts, sanctified places, prophecies, ethics, or organizations, that generally relate 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. 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

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 (thermodynamics), work, and temperature, and their relation to energy, entropy, and the physical properties of matter and radiation. The behavior of these quantities is governed b ...
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 Pierre Curie ( ; ; 15 May 1859 – 19 April 1906) was a French physicist, Radiochemistry, radiochemist, and a pioneer in crystallography, magnetism, piezoelectricity, and radioactivity. He shared the 1903 Nobel Prize in Physics with his wife, ...
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
isotope Isotopes are distinct nuclear species (or ''nuclides'') of the same chemical element. They have the same atomic number (number of protons in their Atomic nucleus, nuclei) and position in the periodic table (and hence belong to the same chemica ...
s 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.


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 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

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 2023/09are 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: 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 ICC pre-Cambrian timeline (v2024/12, current ), 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:-4567 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: -4031 till: -2500 text:Archean color:archean from: start till: -4031 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: -4031 till: -3600 text:Eoarchean color:eoarchean from: start till: -4031 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 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. these proposed changes have not been accepted by the ICS. The proposed changes (changes from the current scale 2023/09 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 Continental crust is the layer of igneous, metamorphic, and sedimentary 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 '' si ...
. *** ''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
prokaryote A prokaryote (; less commonly spelled procaryote) is a unicellular organism, single-celled organism whose cell (biology), cell lacks a cell nucleus, nucleus and other membrane-bound organelles. The word ''prokaryote'' comes from the Ancient Gree ...
s *** 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
eukaryote The eukaryotes ( ) constitute the Domain (biology), domain of Eukaryota or Eukarya, organisms whose Cell (biology), cells have a membrane-bound cell nucleus, nucleus. All animals, plants, Fungus, fungi, seaweeds, and many unicellular organisms ...
s. *** ''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: 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:-4567.3 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: -541 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: -541 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: -541 text:Ediacaran color:ediacaran from: -850 till: -630 text:Cryogenian 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 ICC pre-Cambrian timeline (v2024/12, current ), 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:-4567.3 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: -4031 till: -2500 text:Archean color:archean from: start till: -4031 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: -4031 till: -3600 text:Eoarchean color:eoarchean from: start till: -4031 color:white bar:System/Period fontsize:7 from: -635 till: -538.8 text:Ediacaran color:ediacaran from: -720 till: -635 text:Cryogenian 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 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. 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. The International Commission on Stratigraphy also provide an online interactive version of this chart. The interactive version is based on a service delivering a machine-readable Resource Description Framework/ Web Ontology Language 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 and satellites in the
Solar System The Solar SystemCapitalization 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 "Sola ...
have sufficiently rigid structures to have preserved records of their own histories, for example, Venus, Mars and the Earth's
Moon The Moon is Earth's only natural satellite. It Orbit of the Moon, orbits around Earth at Lunar distance, an average distance of (; about 30 times Earth diameter, Earth's diameter). The Moon rotation, rotates, with a rotation period (lunar ...
. 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 Geomorphology () is the scientific study of the origin and evolution of topography, topographic and bathymetry, bathymetric features generated by physical, chemical or biological processes operating at or near Earth#Surface, Earth's surface. Ge ...
markers, namely impact cratering, volcanism, and
erosion Erosion is the action of surface processes (such as Surface runoff, water flow or wind) that removes soil, Rock (geology), rock, or dissolved material from one location on the Earth's crust#Crust, Earth's crust and then sediment transport, tran ...
. 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.


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 on board the
Mars Express ''Mars Express'' is a space exploration mission by the European Space Agency, European Space Agency (ESA) exploring the planet Mars and its moons since 2003, and the first planetary mission attempted by ESA. ''Mars Express'' consisted of two ...
. 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 (astrophysics), accretion, or Internal structure of Earth, core formation, or of the material from which Earth formed. This dating ...
* Cosmic calendar * Deep time * Evolutionary history of life * Formation and evolution of the Solar System * Geological history of Earth * Geology of Mars * Geon (geology) * History of Earth * History of geology * History of paleontology * List of fossil sites * List of geochronologic names * Lunar geologic timescale * Martian geologic timescale * 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


Notes


References


Further reading

* * * * * * * * * * * * * * *Montenari, Michael (2022)
Integrated Quaternary Stratigraphy
(1st ed.). Amsterdam: Academic Press (Elsevier). ISBN 978-0-323-98913-8. *Montenari, Michael (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
' (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


(archived 18 April 2005)
GSA: Geologic Time Scale
(archived 20 January 2019)


GeoWhen Database
(archived 23 June 2004)

(archived 11 November 2005)
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


(archived 14 July 2011)
Deep Time – A History of the Earth : Interactive InfographicGeology Buzz: Geologic Time Scale
. {{Authority control + Natural history Evolution-related timelines Geochronology Articles which contain graphical timelines International Commission on Stratigraphy geologic time scale of Earth