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Geologic time scale

The geologic time scale or geological time scale (GTS) is a representation of time based on the rock record of Earth. It is a system of chronological dating that uses chronostratigraphy (the process of relating strata to time) and geochronology (a scientific branch of geology 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 fossils. The definition of standardised international units of geologic time is the responsibility of the International Commission on Stratigraphy (ICS), a constituent body of the International Union of Geological Sciences (IUGS), whose primary objective is to precisely define global chronostratigraphic units of the International Chronostratigraphic Chart (ICC) 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 conforms to the nomenclature, ages, and colour codes set forth by the ICS.

Principles
The geologic time scale is a way of representing deep time based on events that have occurred throughout Earth's history, a time span of about 4.54 ± 0.05 Ga (4.54 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 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 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 – 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 a correlation of the stratum even when the horizon between them is not continuous.
 * Cross-cutting relationships – A rock feature that cuts across another feature must be younger than the rock it cuts across.
 * 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 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) or relative means (e.g., stratigraphic position, paleomagnetism, 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 often 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 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 changed, merely the geochronometry has been refined.

The numeric values on the ICC are represented by the unit Ma (megaannum) 'million years', i.e.,  Ma, the lower boundary of the Jurassic Period, is defined as 201,400,000 years old with an uncertainty of 200,000 years. Other SI prefix units commonly used by geologists are Ga (gigaannum, billion years), and ka (kiloannum, thousand years), with the latter often represented in calibrated units (before present).

Divisions of geologic time

 * An  is the largest geochronologic time unit and is equivalent to a chronostratigraphic eonothem. There are four formally defined eons: the Hadean, Archean, Proterozoic and Phanerozoic.
 * An  is the second largest geochronologic time unit and is equivalent to a chronostratigraphic erathem. There are ten defined eras: the Eoarchean, Paleoarchean, Mesoarchean, Neoarchean, Paleoproterozoic, Mesoproterozoic, Neoproterozoic, Paleozoic, Mesozoic and Cenozoic, with none from the Hadean eon.
 * A  is equivalent to a chronostratigraphic system. There are 22 defined periods, with the current being the Quaternary period. As an exception two subperiods are used for the Carboniferous Period.
 * An  is the second smallest geochronologic unit. It is equivalent to a chronostratigraphic series. There are 37 defined epochs and one informal one. 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 and is equivalent to a chronostratigraphic stage. There are 96 formal and five informal ages.
 * 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 and  subdivisions are used as the geochronologic equivalents of the chronostratigraphic  and, e.g., Early Triassic Period (geochronologic unit) is used in place of Lower Triassic Series (chronostratigraphic unit).

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 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 becomes the Phanerozoic Eon). Names of erathems in the Phanerozoic were chosen to reflect major changes in the history of life on Earth: Paleozoic (old life), Mesozoic (middle life), and Cenozoic (new life). Names of systems are diverse in origin, with some indicating chronologic position (e.g., Paleogene), while others are named for lithology (e.g., Cretaceous), geography (e.g., Permian), or are tribal (e.g., Ordovician) in origin. Most currently recognised series and subseries are named for their position within a system/series (early/middle/late); however, the ICS 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).

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. Xenophanes of Colophon (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 (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 was also recognised by Chinese naturalist Shen Kuo (1031–1095) and Islamic scientist-philosophers, notably the Brothers of Purity, who wrote on the processes of stratification over the passage of time in their treatises. Their work likely inspired that of the 11th-century Persian polymath Avicenna (Ibn Sînâ, 980–1037) who wrote in The Book of Healing (1027) on the concept of stratification and superposition, pre-dating Nicolas Steno by more than six centuries. Avicenna also recognised fossils as "petrifications of the bodies of plants and animals", with the 13th-century Dominican bishop Albertus Magnus (c. 1200–1280) extending this into a theory of a petrifying fluid. These works appeared to have little influence on scholars in Medieval Europe who looked to the Bible to explain the origins of fossils and sea-level changes, often attributing these to the 'Deluge', including Ristoro d'Arezzo in 1282. It was not until the Italian Renaissance when Leonardo da Vinci (1452–1519) would reinvigorate the relationships between stratification, relative sea-level change, and time, denouncing attribution of fossils to the 'Deluge':

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

These views of da Vinci remained unpublished, and thus lacked influence at the time; however, questions of fossils and their significance were pursued and, while views against Genesis were not readily accepted and dissent from religious doctrine was in some places unwise, scholars such as Girolamo Fracastoro shared da Vinci's views, and found the attribution of fossils to the 'Deluge' absurd.

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: 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.
 * 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.

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 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, 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 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 or orbital physics. These estimations varied from 15,000 million years to 0.075 million years depending on method and author, but the estimations of Lord Kelvin and Clarence King were held in high regard at the time due to their pre-eminence in physics and geology. All of these early geochronometric determinations would later prove to be incorrect.

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

Modern international 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.

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.

Shields et al. 2021
An international working group of the ICS on pre-Cryogenian chronostratigraphic subdivision have 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 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 [v2023/09] are italicised): Proposed pre-Cambrian timeline (Shield et al. 2021, ICS working group on pre-Cryogenian chronostratigraphy), shown to scale: Current ICC pre-Cambrian timeline (v2023/09), shown to scale:
 * 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)

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, 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 [v2023/09]) are italicised:

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

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

Current ICC pre-Cambrian timeline (v2023/09), shown to scale:

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.

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/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 have sufficiently rigid structures to have preserved records of their own histories, for example, Venus, Mars and the Earth's Moon. Dominantly fluid planets, such as the giant planets, do not comparably preserve their history. Apart from the Late Heavy Bombardment, events on other planets probably had little direct influence on the Earth, and events on Earth had correspondingly little effect on those planets. Construction of a time scale that links the planets is, therefore, of only limited relevance to the Earth's time scale, except in a Solar System context. The existence, timing, and terrestrial effects of the Late Heavy Bombardment are still a matter of debate.

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

title: Geologic time scale


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Talk:Geologic time scale

Any citation for the term "epoch" as meaning a span (rather than moment) of time?
The article uses the word epoch to mean a span of time less than an era. In chronology, the term specifies a specific moment in time. Using the latter definition, the current favourite proposed epoch for the Anthropocene is 1950; the epoch for the Holocene is "approximately 11,650 cal years before present". Wiktionary gives both senses (though five of the six use the 'moment' meaning). So I expected to find here a source for the 'time span' meaning, but failed to find it. Under #Terminology, we have Eons are divided into eras,[2] which are in turn divided into periods,[3] epochs and ages. No citation is given for 'epochs' or 'ages'.

Citation 2 above [Chapter 9 of Stratigraphic Guide] just says a. Definition. The series is a chronostratigraphic unit ranking above a stage and below a system. The geochronologic equivalent of a series is an epoch. I don't have Citation 3 [the AGI  Glossary of geology] but it is curious that we have citations for eras and periods, but not for epochs and ages (and don't even mention 'series'. Nor 'stage' nor 'system', for that matter.).

Would someone rectify, please? --John Maynard Friedman (talk) 11:48, 1 February 2022 (UTC)

 * I found it surprisingly difficult to find a clear definition - I note that both Epoch (geology) and Age (geology) unhelpfully redirect to this page. I think that this source should cover this, both for "epochs" and "ages", even if it doesn't go into any detail about the latter. Mikenorton (talk) 12:55, 1 February 2022 (UTC)
 * I suggest it would be a good idea to expand the #Terminology section to define and explain all these terms. That really needs some subject expertise that I don't have. I don't think that just whacking in a citation arbitrarily will do. --John Maynard Friedman (talk) 17:21, 1 February 2022 (UTC)

 * This is what I was looking for. It contains everything that we need to write a more comprehensive terminology section as you suggest. I will do my best to get around to doing this, if nobody else gets there first. Mikenorton (talk) 17:41, 1 February 2022 (UTC)
 * Hi @Mikenorton I've started work on writing a much more comprehensive terminology Draft: GeologicTimeScale Terminology and am happy to take the lead on this. If you have time and feel like helping out that would be much appreciated and would speed up the process. Given I'm planning a substantial rewrite I thought it would be easier to write a draft first and then replace the current terminology section on this page. Jarred C Lloyd (talk) 05:47, 2 April 2022 (UTC)
 * Good news, I keep getting involved in other things. Currently away and with little opportunity to edit, so will hopefully take a look on my return, thanks, Mikenorton (talk) 14:38, 2 April 2022 (UTC)
 * In passing, I was surprised to see this in the ICS item to which you linked @Mikenorton: An eonothem is a chronostratigraphic unit greater than an erathem. The geochronologic equivalent is an eon. Three eonothems are generally recognized, from older to younger, the Archean, Proterozoic and Phanerozoic eonothems. The combined first two are usually referred to as the Precambrian. - it rather ignores the Hadean and equates just the combined Archaean and Proterozoic eon(othem)s with the Precambrian; a definition from an august body at odds with the general understanding of the supereon and indeed with its own published chart. A simple error on the part of ICS? cheers Geopersona (talk) 07:18, 26 April 2022 (UTC)
 * I think that may be a deliberate omission of the Hadean in that definition by the ICS as they are only talking about the formally defined eonothems/eons. As you point out the general use of pre-Cambrian includes the Hadean (as does their latest chart [although both are still informal as indicated by italics]), but neither are formal chronostratigraphic names/terms. The better definition which I've used in this revision of the article I'm working on, is "Informally, the time before the Cambrian is often referred to as the pre-Cambrian or Precambrian (Supereon)". Jarred C Lloyd (talk) 07:46, 26 April 2022 (UTC)
 * There are plainly nuances here - I'm leaving a clearer exposition of all this in your hands. thanks Geopersona (talk) 08:02, 26 April 2022 (UTC)

Dates in 'Proposed Precambrian Timeline' section
I was about to change the Precambrian/Cambrian boundary dates (of which there are 3 occurrences) from 541 Ma to 539 Ma in accordance with the recently published ICS chart (as featured elsewhere in this article and many others) but then wondered if this section is intended in full to describe the situation in 2012 in which case it might be appropriate, if confusing, to retain the 541 figure as part of the proposals set out at that time. The section as a whole perhaps needs updating from the perspective of April 2022. Geopersona (talk) 06:42, 26 April 2022 (UTC)

 * Good pick up @Geopersona as in my above reply (about eons), I'm working on revising this entire article. Because I'm making some substantial revisions I've been drafting it on my user page so I don't break this one for now. I'll make sure I adjust the dates in a sensible way for this. If you feel like helping out or providing some commentary on it, pop it on here and I'll be sure to look into it. Jarred C Lloyd (talk) 07:56, 26 April 2022 (UTC)
 * Yes, sounds good to me - good luck! cheers Geopersona (talk) 08:02, 26 April 2022 (UTC)
 * The entire Proposal section has been deleted. Why? 2601:441:4900:A6E0:91A4:2688:B6B:98E5 (talk) 02:10, 9 July 2022 (UTC)
 * I think it was archived: a perfectly normal procedure. Feline Hymnic (talk) 09:18, 9 July 2022 (UTC)
 * If the proposal section that is being referred to was "Proposed Precambrian timeline", it has not been deleted but actually expanded within the section Geologic_time_scale section, which includes the previous content, Anthropocene, and another proposal for the Precambrian of the ICC. Jarred C Lloyd (talk) 12:39, 11 July 2022 (UTC)

Revision of article
To those who are interested (@Geopersona, @Mikenorton, @Benniboi01, @User:GeoWriter?, please ignore if not interested) I've drafted a substantial revision to this article intially spurred on by the commentary above by @User:John Maynard Friedman. I drafted it seperately from this page as I have been making a lot of edits and it was easier to build upon the existing article content this way. I'd like to try elevate this article quality rating. This revision can be found here.

I've also made a new figure to replace the "clock" lead image to try adress previous criticism and have a more senisble progression (I do find a circle to be an odd representation of a linear timeline). I'm not "attached" to this figure and can retain the current circle if other editors prefer it. I've only got the final section (about non-Earth geologic time scales) to finish writing, and copyedit to fix spelling errors etc. The final section will incorporate the times (in the Hadean) I removed from the main table of geologic time that are non-Earth divisions as IMO these are conflating Earth's geologic time scale and the Moon's geologic time scale in an article spefically about Earth's geotime.

It would be much appreciated if I could have a second pair of eyes run over the draft, comment on layout (order of sections), comment on the newer lead image, suggest improvements (i.e. point out critical flaws) they think need to be made before incorporatating it into this main article etc. I'll start incorporating the changes from next Thursday (Aus time) when I return from field work. Jarred C Lloyd (talk) 07:18, 4 May 2022 (UTC)

 * At first glance, looking good. I won't be able to do a proper comparison until I get back from my current trip and can look at them side by side on a large screen, rather than the tablet I've got with me. Mikenorton (talk) 13:18, 4 May 2022 (UTC)

 * I just took a look and I have one issue with it at the moment (aside from minor formatting issues which aren't really that important). I think it might be better if we change the bulleted list in the "terminology" section into prose, since a lot of those terms don't make sense to me to include in a list format like that. Otherwise, I think the draft is pretty solid. I especially like the new "principles" section, as it provides a nice way to link pages that are otherwise rarely mentioned elsewhere, while also providing some new info. Benniboi01 (talk) 16:29, 7 May 2022 (UTC)
 * I've removed the bullet point formatting as per your suggestion, as they were written in prose anyway. I had the bulleted list originally to clearly delineate linked concepts and key concepts, but I think they are clear enough as I have them now anyway. What minor formatting issues are you eluding to? I've likely just missed them in my drafting process. Jarred C Lloyd (talk) 01:55, 12 May 2022 (UTC)

Any objections to me implementing the revised article (see here) and lead image? I've only got a tiny bit to add in the last section of the draft on Non-Earth based geologic time scales. It's a substantial rewrite of the page and I want to give a final heads up before I implement it. Obviously formatting/style may need to be adjusted afterwards if I've missed something or parts don't fit the MOS. Jarred C Lloyd (talk) 05:32, 25 May 2022 (UTC)

Personally, I really miss the horizontal time scale that presented Earth's geologic time at different scales, as seen in this revision (dated 18 May 2021—perhaps it also appears in later revisions, but there have been a lot of changes to the page since then). I find it the most readable and easily scanned version for just getting a sense of whole the epochs unfold across eons, etc. Is there anyway to bring that version back somewhere? I'm sorry I haven't followed the discussions that led to its disappearance, but I get frustrated everytime I return to this page to look up information about specific epochs, because I found that earlier version much more fun and easy to search than what I has appeared since. Thomascantor (talk) 15:27, 25 November 2022 (UTC)

 * @Thomascantor do you mean the multiple scale horizontal time scale that is in the Terminology section of the revision you have linked? if so, it is still in the article, but at the end of the Modern International Timescale subsection of the History section. I moved it when I revised the article to better separate the themes of a given section. Jarred C Lloyd (talk) 22:56, 25 November 2022 (UTC)
 * Ah, I see it now. Thanks, Jarred C Lloyd, for the clarification and help. Thomascantor (talk) 21:50, 28 November 2023 (UTC)

Merging the geological timeline articles? Geologic time scale - Timeline of the evolutionary history of life - Timeline of human evolution
I am interested in the past of Earth and life, a fan of extinct lifeforms, but I am not an expert in any relevant field, i.e. I am not a professional geologist, palaeontologist, palaeoclimatologist or something like that.

Nevertheless, while browsing articles, I found this article to significantly overlap with Timeline of the evolutionary history of life and at least partially with Timeline of human evolution. Thus I propose merging this article with Timeline of the evolutionary history of life and refocusing Timeline of human evolution towards Hominidae or at least primate evolution specific dates. Of course, the first Bilateria represent an important milestone, but such milestones can be explained in this article or Timeline of the evolutionary history of life in my opinion. PragmaFisch (talk) 17:11, 11 November 2023 (UTC)

 * You apparently don't understand the timescale. Evolutionary and geological are very different. --Fama Clamosa (talk) 19:26, 11 November 2023 (UTC)
 * I do see the point - however, Geologic time scale contains quite a lot of information on life and its evolution, too. Might that be better suited to Timeline of the evolutionary history of life? Also, I love Geologic time scale most because the scrollable timetable with the common colours and explanations etc. which provides an excellent overview. Maybe this at least could be incorporated into Timeline of the evolutionary history of life? PragmaFisch (talk) 19:34, 11 November 2023 (UTC)
 * Oppose Despite some extent of overlap given their geological natures, geologic time scale and timeline of the evolutionary history of life are two different concepts, the former focusing on the stratigraphic side and the latter focusing on the paleobiological side. Merging the two pages would result in an excessively long page. They both can overlap in discussing stratigraphic ranges of life forms, but for the geologic time scale page, it's not the main topic. PrimalMustelid (talk) 19:01, 12 November 2023 (UTC)
 * I would be opposed to merging the two, as the only real overlap seems to be the fact that they both use the same division of deep time and the fact that the timeline on this article also has some information on what was happening at the time, also pertaining to life that existed. The topics they cover (those being stratigraphic and paleobiological) are quite far apart, and merging them together would result in a much messier article than either of the two seperate ones. The Morrison Man (talk) 15:57, 13 November 2023 (UTC)
 * Oppose - the timelines each have a different scope: geological development of Earth, lifeforms, human lifeform; each of which needs its own chronological reckoning.  — The Transhumanist   11:16, 30 April 2024 (UTC)

 * Oppose - There is inevitably some overlap between the timelines but any sort of combined timeline would not, in my view, do any of the topics justice. Mikenorton (talk) 13:49, 30 April 2024 (UTC)
 * Oppose - While there is some overlap due to the nature of how geological time is defined and how biologicial evolution in inherently linked with geologic processes, merging of the two articles would not do either topic justice. As it stands, I believe both articles are able to elaborate on their specific topics in better detail and with greater cohesion and readability than a merged article would be able to do.  Jarred C Lloyd (talk) 12:11, 1 May 2024 (UTC)

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

title: Talk:Geologic time scale


text:
Gambler's fallacy

The gambler's fallacy, also known as the Monte Carlo fallacy or the fallacy of the maturity of chances, is the belief that, if an event (whose occurrences are independent and identically distributed) has occurred less frequently than expected, it is more likely to happen again in the future (or vice versa). The fallacy is commonly associated with gambling, where it may be believed, for example, that the next dice roll is more than usually likely to be six because there have recently been fewer than the expected number of sixes.

The term "Monte Carlo fallacy" originates from an example of the phenomenon, in which the roulette wheel spun black 26 times in succession at the Monte Carlo Casino in 1913.

Coin toss
The gambler's fallacy can be illustrated by considering the repeated toss of a fair coin. The outcomes in different tosses are statistically independent and the probability of getting heads on a single toss is $1⁄2$ (one in two). The probability of getting two heads in two tosses is $1⁄4$ (one in four) and the probability of getting three heads in three tosses is $1⁄8$ (one in eight). In general, if Ai is the event where toss i of a fair coin comes up heads, then:
 * $$\Pr\left(\bigcap_{i=1}^n A_i\right)=\prod_{i=1}^n \Pr(A_i)={1\over2^n}$$.

If after tossing four heads in a row, the next coin toss also came up heads, it would complete a run of five successive heads. Since the probability of a run of five successive heads is $1⁄32$ (one in thirty-two), a person might believe that the next flip would be more likely to come up tails rather than heads again. This is incorrect and is an example of the gambler's fallacy. The event "5 heads in a row" and the event "first 4 heads, then a tails" are equally likely, each having probability $1⁄32$. Since the first four tosses turn up heads, the probability that the next toss is a head is:
 * $$\Pr\left(A_5|A_1 \cap A_2 \cap A_3 \cap A_4 \right)=\Pr\left(A_5\right)=\frac{1}{2}$$.

While a run of five heads has a probability of $1⁄32$ = 0.03125 (a little over 3%), the misunderstanding lies in not realizing that this is the case only before the first coin is tossed. After the first four tosses in this example, the results are no longer unknown, so their probabilities are at that point equal to 1 (100%). The probability of a run of coin tosses of any length continuing for one more toss is always 0.5. The reasoning that a fifth toss is more likely to be tails because the previous four tosses were heads, with a run of luck in the past influencing the odds in the future, forms the basis of the fallacy.

Why the probability is 1/2 for a fair coin
If a fair coin is flipped 21 times, the probability of 21 heads is 1 in 2,097,152. The probability of flipping a head after having already flipped 20 heads in a row is $1⁄2$. Assuming a fair coin:
 * The probability of 20 heads, then 1 tail is 0.520 × 0.5 = 0.521
 * The probability of 20 heads, then 1 head is 0.520 × 0.5 = 0.521

The probability of getting 20 heads then 1 tail, and the probability of getting 20 heads then another head are both 1 in 2,097,152. When flipping a fair coin 21 times, the outcome is equally likely to be 21 heads as 20 heads and then 1 tail. These two outcomes are equally as likely as any of the other combinations that can be obtained from 21 flips of a coin. All of the 21-flip combinations will have probabilities equal to 0.521, or 1 in 2,097,152. Assuming that a change in the probability will occur as a result of the outcome of prior flips is incorrect because every outcome of a 21-flip sequence is as likely as the other outcomes. In accordance with Bayes' theorem, the likely outcome of each flip is the probability of the fair coin, which is $1⁄2$.

Other examples
The fallacy leads to the incorrect notion that previous failures will create an increased probability of success on subsequent attempts. For a fair 16-sided die, the probability of each outcome occurring is $1⁄16$ (6.25%). If a win is defined as rolling a 1, the probability of a 1 occurring at least once in 16 rolls is:
 * $$1-\left[\frac{15}{16}\right]^{16} \,=\, 64.39\%$$

The probability of a loss on the first roll is $15⁄16$ (93.75%). According to the fallacy, the player should have a higher chance of winning after one loss has occurred. The probability of at least one win is now:
 * $$1-\left[\frac{15}{16}\right]^{15} \,=\, 62.02\%$$

By losing one toss, the player's probability of winning drops by two percentage points. With 5 losses and 11 rolls remaining, the probability of winning drops to around 0.5 (50%). The probability of at least one win does not increase after a series of losses; indeed, the probability of success actually decreases, because there are fewer trials left in which to win. The probability of winning will eventually be equal to the probability of winning a single toss, which is $1⁄16$ (6.25%) and occurs when only one toss is left.

Reverse position
After a consistent tendency towards tails, a gambler may also decide that tails has become a more likely outcome. This is a rational and Bayesian conclusion, bearing in mind the possibility that the coin may not be fair; it is not a fallacy. Believing the odds to favor tails, the gambler sees no reason to change to heads. However it is a fallacy that a sequence of trials carries a memory of past results which tend to favor or disfavor future outcomes.

The inverse gambler's fallacy described by Ian Hacking is a situation where a gambler entering a room and seeing a person rolling a double six on a pair of dice may erroneously conclude that the person must have been rolling the dice for quite a while, as they would be unlikely to get a double six on their first attempt.

Retrospective gambler's fallacy
Researchers have examined whether a similar bias exists for inferences about unknown past events based upon known subsequent events, calling this the "retrospective gambler's fallacy".

An example of a retrospective gambler's fallacy would be to observe multiple successive "heads" on a coin toss and conclude from this that the previously unknown flip was "tails". Real world examples of retrospective gambler's fallacy have been argued to exist in events such as the origin of the Universe. In his book Universes, John Leslie argues that "the presence of vastly many universes very different in their characters might be our best explanation for why at least one universe has a life-permitting character". Daniel M. Oppenheimer and Benoît Monin argue that "In other words, the 'best explanation' for a low-probability event is that it is only one in a multiple of trials, which is the core intuition of the reverse gambler's fallacy." Philosophical arguments are ongoing about whether such arguments are or are not a fallacy, arguing that the occurrence of our universe says nothing about the existence of other universes or trials of universes. Three studies involving Stanford University students tested the existence of a retrospective gamblers' fallacy. All three studies concluded that people have a gamblers' fallacy retrospectively as well as to future events. The authors of all three studies concluded their findings have significant "methodological implications" but may also have "important theoretical implications" that need investigation and research, saying "[a] thorough understanding of such reasoning processes requires that we not only examine how they influence our predictions of the future, but also our perceptions of the past."

Childbirth
In 1796, Pierre-Simon Laplace described in A Philosophical Essay on Probabilities the ways in which men calculated their probability of having sons: "I have seen men, ardently desirous of having a son, who could learn only with anxiety of the births of boys in the month when they expected to become fathers. Imagining that the ratio of these births to those of girls ought to be the same at the end of each month, they judged that the boys already born would render more probable the births next of girls." The expectant fathers feared that if more sons were born in the surrounding community, then they themselves would be more likely to have a daughter. This essay by Laplace is regarded as one of the earliest descriptions of the fallacy. Likewise, after having multiple children of the same sex, some parents may erroneously believe that they are due to have a child of the opposite sex.

Monte Carlo Casino
An example of the gambler's fallacy occurred in a game of roulette at the Monte Carlo Casino on August 18, 1913, when the ball fell in black 26 times in a row. This was an extremely unlikely occurrence: the probability of a sequence of either red or black occurring 26 times in a row is $(18⁄37)^{26-1}$ or around 1 in 66.6 million, assuming the mechanism is unbiased. Gamblers lost millions of francs betting against black, reasoning incorrectly that the streak was causing an imbalance in the randomness of the wheel, and that it had to be followed by a long streak of red.

Non-independent events
The gambler's fallacy does not apply when the probability of different events is not independent. In such cases, the probability of future events can change based on the outcome of past events, such as the statistical permutation of events. An example is when cards are drawn from a deck without replacement. If an ace is drawn from a deck and not reinserted, the next card drawn is less likely to be an ace and more likely to be of another rank. The probability of drawing another ace, assuming that it was the first card drawn and that there are no jokers, has decreased from $4⁄52$ (7.69%) to $3⁄51$ (5.88%), while the probability for each other rank has increased from $4⁄52$ (7.69%) to $4⁄51$ (7.84%). This effect allows card counting systems to work in games such as blackjack.

Bias
In most illustrations of the gambler's fallacy and the reverse gambler's fallacy, the trial (e.g. flipping a coin) is assumed to be fair. In practice, this assumption may not hold. For example, if a coin is flipped 21 times, the probability of 21 heads with a fair coin is 1 in 2,097,152. Since this probability is so small, if it happens, it may well be that the coin is somehow biased towards landing on heads, or that it is being controlled by hidden magnets, or similar. In this case, the smart bet is "heads" because Bayesian inference from the empirical evidence — 21 heads in a row — suggests that the coin is likely to be biased toward heads. Bayesian inference can be used to show that when the long-run proportion of different outcomes is unknown but exchangeable (meaning that the random process from which the outcomes are generated may be biased but is equally likely to be biased in any direction) and that previous observations demonstrate the likely direction of the bias, the outcome which has occurred the most in the observed data is the most likely to occur again.

For example, if the a priori probability of a biased coin is say 1%, and assuming that such a biased coin would come down heads say 60% of the time, then after 21 heads the probability of a biased coin has increased to about 32%.

The opening scene of the play Rosencrantz and Guildenstern Are Dead by Tom Stoppard discusses these issues as one man continually flips heads and the other considers various possible explanations.

Changing probabilities
If external factors are allowed to change the probability of the events, the gambler's fallacy may not hold. For example, a change in the game rules might favour one player over the other, improving his or her win percentage. Similarly, an inexperienced player's success may decrease after opposing teams learn about and play against their weaknesses. This is another example of bias.

Origins
The gambler's fallacy arises out of a belief in a law of small numbers, leading to the erroneous belief that small samples must be representative of the larger population. According to the fallacy, streaks must eventually even out in order to be representative. Amos Tversky and Daniel Kahneman first proposed that the gambler's fallacy is a cognitive bias produced by a psychological heuristic called the representativeness heuristic, which states that people evaluate the probability of a certain event by assessing how similar it is to events they have experienced before, and how similar the events surrounding those two processes are. According to this view, "after observing a long run of red on the roulette wheel, for example, most people erroneously believe that black will result in a more representative sequence than the occurrence of an additional red", so people expect that a short run of random outcomes should share properties of a longer run, specifically in that deviations from average should balance out. When people are asked to make up a random-looking sequence of coin tosses, they tend to make sequences where the proportion of heads to tails stays closer to 0.5 in any short segment than would be predicted by chance, a phenomenon known as insensitivity to sample size. Kahneman and Tversky interpret this to mean that people believe short sequences of random events should be representative of longer ones. The representativeness heuristic is also cited behind the related phenomenon of the clustering illusion, according to which people see streaks of random events as being non-random when such streaks are actually much more likely to occur in small samples than people expect.

The gambler's fallacy can also be attributed to the mistaken belief that gambling, or even chance itself, is a fair process that can correct itself in the event of streaks, known as the just-world hypothesis. Other researchers believe that belief in the fallacy may be the result of a mistaken belief in an internal locus of control. When a person believes that gambling outcomes are the result of their own skill, they may be more susceptible to the gambler's fallacy because they reject the idea that chance could overcome skill or talent.

Variations
Some researchers believe that it is possible to define two types of gambler's fallacy: type one and type two. Type one is the classic gambler's fallacy, where individuals believe that a particular outcome is due after a long streak of another outcome. Type two gambler's fallacy, as defined by Gideon Keren and Charles Lewis, occurs when a gambler underestimates how many observations are needed to detect a favorable outcome, such as watching a roulette wheel for a length of time and then betting on the numbers that appear most often. For events with a high degree of randomness, detecting a bias that will lead to a favorable outcome takes an impractically large amount of time and is very difficult, if not impossible, to do. The two types differ in that type one wrongly assumes that gambling conditions are fair and perfect, while type two assumes that the conditions are biased, and that this bias can be detected after a certain amount of time.

Another variety, known as the retrospective gambler's fallacy, occurs when individuals judge that a seemingly rare event must come from a longer sequence than a more common event does. The belief that an imaginary sequence of die rolls is more than three times as long when a set of three sixes is observed as opposed to when there are only two sixes. This effect can be observed in isolated instances, or even sequentially. Another example would involve hearing that a teenager has unprotected sex and becomes pregnant on a given night, and concluding that she has been engaging in unprotected sex for longer than if we hear she had unprotected sex but did not become pregnant, when the probability of becoming pregnant as a result of each intercourse is independent of the amount of prior intercourse.

Relationship to hot-hand fallacy
Another psychological perspective states that gambler's fallacy can be seen as the counterpart to basketball's hot-hand fallacy, in which people tend to predict the same outcome as the previous event - known as positive recency - resulting in a belief that a high scorer will continue to score. In the gambler's fallacy, people predict the opposite outcome of the previous event - negative recency - believing that since the roulette wheel has landed on black on the previous six occasions, it is due to land on red the next. Ayton and Fischer have theorized that people display positive recency for the hot-hand fallacy because the fallacy deals with human performance, and that people do not believe that an inanimate object can become "hot." Human performance is not perceived as random, and people are more likely to continue streaks when they believe that the process generating the results is nonrandom. When a person exhibits the gambler's fallacy, they are more likely to exhibit the hot-hand fallacy as well, suggesting that one construct is responsible for the two fallacies.

The difference between the two fallacies is also found in economic decision-making. A study by Huber, Kirchler, and Stockl in 2010 examined how the hot hand and the gambler's fallacy are exhibited in the financial market. The researchers gave their participants a choice: they could either bet on the outcome of a series of coin tosses, use an expert opinion to sway their decision, or choose a risk-free alternative instead for a smaller financial reward. Participants turned to the expert opinion to make their decision 24% of the time based on their past experience of success, which exemplifies the hot-hand. If the expert was correct, 78% of the participants chose the expert's opinion again, as opposed to 57% doing so when the expert was wrong. The participants also exhibited the gambler's fallacy, with their selection of either heads or tails decreasing after noticing a streak of either outcome. This experiment helped bolster Ayton and Fischer's theory that people put more faith in human performance than they do in seemingly random processes.

Neurophysiology
While the representativeness heuristic and other cognitive biases are the most commonly cited cause of the gambler's fallacy, research suggests that there may also be a neurological component. Functional magnetic resonance imaging has shown that after losing a bet or gamble, known as riskloss, the frontoparietal network of the brain is activated, resulting in more risk-taking behavior. In contrast, there is decreased activity in the amygdala, caudate, and ventral striatum after a riskloss. Activation in the amygdala is negatively correlated with gambler's fallacy, so that the more activity exhibited in the amygdala, the less likely an individual is to fall prey to the gambler's fallacy. These results suggest that gambler's fallacy relies more on the prefrontal cortex, which is responsible for executive, goal-directed processes, and less on the brain areas that control affective decision-making.

The desire to continue gambling or betting is controlled by the striatum, which supports a choice-outcome contingency learning method. The striatum processes the errors in prediction and the behavior changes accordingly. After a win, the positive behavior is reinforced and after a loss, the behavior is conditioned to be avoided. In individuals exhibiting the gambler's fallacy, this choice-outcome contingency method is impaired, and they continue to make risks after a series of losses.

Possible solutions
The gambler's fallacy is a deep-seated cognitive bias and can be very hard to overcome. Educating individuals about the nature of randomness has not always proven effective in reducing or eliminating any manifestation of the fallacy. Participants in a study by Beach and Swensson in 1967 were shown a shuffled deck of index cards with shapes on them, and were instructed to guess which shape would come next in a sequence. The experimental group of participants was informed about the nature and existence of the gambler's fallacy, and were explicitly instructed not to rely on run dependency to make their guesses. The control group was not given this information. The response styles of the two groups were similar, indicating that the experimental group still based their choices on the length of the run sequence. This led to the conclusion that instructing individuals about randomness is not sufficient in lessening the gambler's fallacy.

An individual's susceptibility to the gambler's fallacy may decrease with age. A study by Fischbein and Schnarch in 1997 administered a questionnaire to five groups: students in grades 5, 7, 9, 11, and college students specializing in teaching mathematics. None of the participants had received any prior education regarding probability. The question asked was: "Ronni flipped a coin three times and in all cases heads came up. Ronni intends to flip the coin again. What is the chance of getting heads the fourth time?" The results indicated that as the students got older, the less likely they were to answer with "smaller than the chance of getting tails", which would indicate a negative recency effect. 35% of the 5th graders, 35% of the 7th graders, and 20% of the 9th graders exhibited the negative recency effect. Only 10% of the 11th graders answered this way, and none of the college students did. Fischbein and Schnarch theorized that an individual's tendency to rely on the representativeness heuristic and other cognitive biases can be overcome with age.

Another possible solution comes from Roney and Trick, Gestalt psychologists who suggest that the fallacy may be eliminated as a result of grouping. When a future event such as a coin toss is described as part of a sequence, no matter how arbitrarily, a person will automatically consider the event as it relates to the past events, resulting in the gambler's fallacy. When a person considers every event as independent, the fallacy can be greatly reduced.

Roney and Trick told participants in their experiment that they were betting on either two blocks of six coin tosses, or on two blocks of seven coin tosses. The fourth, fifth, and sixth tosses all had the same outcome, either three heads or three tails. The seventh toss was grouped with either the end of one block, or the beginning of the next block. Participants exhibited the strongest gambler's fallacy when the seventh trial was part of the first block, directly after the sequence of three heads or tails. The researchers pointed out that the participants that did not show the gambler's fallacy showed less confidence in their bets and bet fewer times than the participants who picked with the gambler's fallacy. When the seventh trial was grouped with the second block, and was perceived as not being part of a streak, the gambler's fallacy did not occur.

Roney and Trick argued that instead of teaching individuals about the nature of randomness, the fallacy could be avoided by training people to treat each event as if it is a beginning and not a continuation of previous events. They suggested that this would prevent people from gambling when they are losing, in the mistaken hope that their chances of winning are due to increase based on an interaction with previous events.

Types of users
Within a real-world setting, numerous studies have uncovered that for various decision makers placed in high stakes scenarios, it is likely they will reflect some degree of strong negative autocorrelation in their judgement.

Asylum judges
In a study aimed at discovering if the negative autocorrelation that exists with the gambler's fallacy existed in the decision made by U.S. asylum judges, results showed that after two successive asylum grants, a judge would be 5.5% less likely to approve a third grant.

Baseball umpires
In the game of baseball, decisions are made every minute. One particular decision made by umpires which is often subject to scrutiny is the 'strike zone' decision. Whenever a batter does not swing, the umpire must decide if the ball was within a fair region for the batter, known as the strike zone. If outside of this zone, the ball does not count towards outing the batter. In a study of over 12,000 games, results showed that umpires are 1.3% less likely to call a strike if the previous two balls were also strikes.

Loan officers
In the decision making of loan officers, it can be argued that monetary incentives are a key factor in biased decision making, rendering it harder to examine the gambler's fallacy effect. However, research shows that loan officers who are not incentivised by monetary gain are 8% less likely to approve a loan if they approved one for the previous client.

Lottery players
Lottery play and jackpots entice gamblers around the globe, with the biggest decision for hopeful winners being what numbers to pick. While most people will have their own strategy, evidence shows that after a number is selected as a winner in the current draw, the same number will experience a significant drop in selections in the following lottery. A popular study by Charles Clotfelter and Philip Cook investigated this effect in 1991, where they concluded bettors would cease to select numbers immediately after they were selected, ultimately recovering selection popularity within three months. Soon after, a 1994 study was constructed by Dek Terrell to test the findings of Clotfelter and Cook. The key change in Terrell's study was the examination of a pari-mutuel lottery in which, a number selected with lower total wagers placed on it will result in a higher pay-out. While this examination did conclude that players in both types of lotteries exhibited behaviour in-line with the gambler's fallacy theory, those who took part in pari-mutuel betting seemed to be less influenced.

The effect the of gambler's fallacy can be observed as numbers are chosen far less frequently soon after they are selected as winners, recovering slowly over a two-month period. For example, on the 11th of April 1988, 41 players selected 244 as the winning combination. Three days later only 24 individuals selected 244, a 41.5% decrease. This is the gambler's fallacy in motion, as lottery players believe that the occurrence of a winning combination in previous days will decrease its likelihood of occurring today.

Video game players
Several video games feature the use of loot boxes, a collection of in-game items awarded on opening with random contents set by rarity metrics, as a monetization scheme. Since around 2018, loot boxes have come under scrutiny from governments and advocates on the basis they are akin to gambling, particularly for games aimed at youth. Some games use a special "pity-timer" mechanism, that if the player has opened several loot boxes in a row without obtaining a high-rarity item, subsequent loot boxes will improve the odds of a higher-rate item drop. This is considered to feed into the gambler's fallacy since it reinforces the idea that a player will eventually obtain a high-rarity item (a win) after only receiving common items from a string of previous loot boxes.

title: Gambler's fallacy


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Gilbert Plains

Gilbert Plains is an unincorporated urban community in the Gilbert Plains Municipality, Manitoba, Canada, that was classified as a town prior to January 1, 2015.

It is situated on the Valley River, in the Parkland Region between Riding Mountain National Park and Duck Mountain Provincial Park.

Gilbert Plains was featured during season 3 of the CBC program Still Standing. The episode originally aired on September 5, 2017.

History
Incorporated in 1906, the original townsite was some miles to the south. The community was named for Gilbert Ross, a Métis man who was living in the region when the first European settler, Glenlyon Campbell, arrived.

On 1 January 2015, the Town of Gilbert Plains relinquished its town status when it amalgamated with the Rural Municipality of Gilbert Plains to form the Gilbert Plains Municipality.

Demographics
In the 2021 Census of Population conducted by Statistics Canada, Gilbert Plains had a population of 773 living in 356 of its 407 total private dwellings, a change of NaN% from its 2016 population of 785. With a land area of 2.74 km2, it had a population density of in 2021.

Media
A local newspaper, The Exponent, serviced both Gilbert Plains and its neighboring town, Grandview. The Exponent closed on 24 February 2017, after 117 years of operation.

A weekly non-profit newspaper, The Plain View, published its first issue on 5 June 2018, and has been running ever since. It serves both Gilbert Plains and Grandview.

Transportation
The community is located on Highway 5 and the CN railway line between Dauphin and Grandview, approximately 250 mi northwest of Winnipeg. Gilbert Plains railway station receives Via Rail service. The community previously had an airport.

title: Gilbert Plains


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Gasparo Contarini

Gasparo Contarini (16 October 1483 – 24 August 1542) was an Italian diplomat, cardinal, and Bishop of Belluno. He advocated for dialogue with Protestants during the Reformation. Born in Venice, he served as the Republic's ambassador to Charles V during its war with him. He was the first to explain the time discrepancy in the Magellan–Elcano circumnavigation due to Earth's rotation. He participated in diplomatic efforts and reconciliations, and became a cardinal, even though he was initially a layman. Contarini was a leader in the reform movement within the Roman Catholic Church. He played a role in the papal approval of the Society of Jesus (Jesuits). He was also involved in attempts to restore religious unity in Germany.

Contarini's work, De magistratibus et republica venetorum, praised the Venetian government system for its harmony, fairness, and stability. He described the electoral process, particularly the lottery system for choosing officials, emphasizing fairness and equality. Contarini's depiction of the Doge, Venice's leader, highlighted the balance between symbolic monarchy and the power of civic institutions. He portrayed the Doge as both a regal figure and a representative of the city's republican governance. Contarini's writings aimed to glorify the republican nature of Venice while showcasing its ceremonial and symbolic elements.

Biography
He was born in Venice, the eldest son of Alvise Contarini, of the ancient noble House of Contarini, and his wife Polissena Malpiero. After a thorough scientific and philosophical training at the University of Padua, he began his career in the service of his native city. From September 1520 to August 1525 he was the Republic's ambassador to Charles V, with whom Venice was soon at war, instructed to defend the Republic's alliance with Francis I of France. Though he participated at the Diet of Worms, April 1521, he never saw or spoke with Martin Luther. He accompanied Charles in the Netherlands and Spain.

Contarini was in Spain when the Magellan–Elcano circumnavigation returned in 1522, bringing with them a cargo of spices from the East as well as a scientific curiosity. Although the sailors had carefully recorded every day of the three-year journey since they left Seville, the ship's log was one day earlier than the actual date when they returned to Seville. Contarini was the first European to give a correct explanation of this phenomenon. Since the ship had sailed westward around the world, in the same direction as the apparent motion of the sun in the sky, the sailors had experienced one fewer sunrise than a stationary observer.

He participated at the Congress of Ferrara in 1526 as the Republic's representative; at the Congress the League of Cognac was formed against the Emperor, allying France with Venice and several states of Italy. Later, after the Sack of Rome (1527), he assisted in reconciling the emperor with Clement VII, whose release he had obtained, and with the Republic of Bologna. Upon his return to Venice, he was made a senator and a member of the Great Council.

Cardinalate
In 1535, Paul III unexpectedly made the secular diplomat a cardinal in order to bind an able man of evangelical disposition to the Roman interests. Contarini accepted, but in his new position did not exhibit his former independence. At the time he was promoted to cardinal, May 21, 1535, he was still a layman. However, already in October 1536 he was appointed Bishop of Belluno. One of the fruits of his diplomatic activity is his De magistratibus et republica Venetorum.

As Cardinal, Contarini figured among the most prominent of the Spirituali, the leaders of the movement for reform within the Roman church. In April 1536 Paul III appointed a commission to devise ways for a reformation, with Contarini presiding. Paul III received favorably Contarini's Consilium de Emendanda Ecclesia, which was circulated among the cardinalate, but it remained a dead letter. Contarini in a letter to his friend Cardinal Reginald Pole (dated 11 November 1538) says that his hopes had been wakened anew by the pope's attitude. He and his friends, who formed the Catholic evangelical movement of the Spirituali, thought that all would have been done when the abuses in church life had been put away. What Contarini had to do with it is shown by his letters to the pope in which he complained of the schism in the church, of simony and flattery in the papal court, but above all of papal tyranny, its least grateful passages. Paul's successor Paul IV, once a member on the commission, in 1539 put it on the Index Librorum Prohibitorum.

In 1541 Cardinal Contarini was papal legate at the Conference of Regensburg, the diet and religious debate marking the culmination of attempts to restore religious unity in Germany by means of conferences. There everything was unfavorable; the Catholic states were bitter, the Evangelicals were distant. Contarini's instructions though apparently free were in fact full of papal reservations. But the papal party had gladly sent him, thinking that through him a union in doctrine could be brought about, while the interest of Rome could be attended to later. Though the princes stood aloof, the theologians and the emperor were for peace, so the main articles were put forth in a formula, Evangelical in thought and Catholic in expression. The papal legate had revised the Catholic proposal and assented to the formula agreed upon. All gave their approval, even Johann Eck, though he later regretted it.

Contarini's theological advisor was Tommaso Badia; his own position is shown in a treatise on justification, composed at Regensburg, which in essential points is Evangelical, differing only in the omission of the negative side and in being interwoven with the teaching of Aquinas. Meanwhile, the papal policy had changed, and Contarini was compelled to follow his leader. He advised the emperor, after the conference had broken up, not to renew it, but to submit everything to the pope.

Ignatius Loyola acknowledged that Cardinal Contarini was largely responsible for the papal approbation of the Society of Jesus, on September 27, 1540. Meanwhile, Rome had drifted further into reaction, and Contarini died while legate at Bologna, at a time when the Inquisition had driven many of his friends and fellows in conviction into exile.

The Commonwealth and Government of Venice
Contarini's book De magistratibus et republica venetorum (Paris, 1543) is an important source for the study of sixteenth- and seventeenth-century Venice's unique system of government. It was published in an English translation in 1599. This magisterial work, written during his time as an ambassador to Charles V, extols the various institutions of the Venetian state in a manner designed to emphasize harmony, fairness and serenity. Historians have demonstrated that this text represents Contarini's idealization of Venetian reality. Probably written for a foreign, courtly audience, this work functions as the source for the everlasting propagation of the "myth of Venice" as a stable, unchanging and prosperous society.

His depiction of how members of the council were elected to the senate, for example, aimed to emphasise the way the electoral system prevented factionalism from occurring, instead making sure that “public benefits are largely extended among the citizens” rather than narrowly amongst “one family”. An elaborate lottery is described as giving the maximum amount of chance in appointing patricians to particular offices, and care is taken to point out if two of one family are standing for similar posts. Fairness is further emphasised in Contarini's constant references to the equality the members of the council enjoyed. They “sit down where it pleases them, for there is no place appointed to any”, and they “with oath promise to do their utmost diligence, that the laws may be observed”. He creates an image of disparate individuals, with factions broken up by the guiding hand of the law, working to ensure those in positions of importance are fairly chosen from their number and without the capacity to serve the interests of a smaller group.

Contarini's depiction of the Doge lucidly demonstrates the way in which this figure embodies both the conscious illusion of a resplendent monarchical ruler and an equally conscious demonstration of a regime that wishes to portray itself as ruled by many limiting the powers of one. This calculated duality means that Contarini's doge, which the second book of De magistratibus is almost entirely devoted to discussing, represents the closest point in his text to what actually occurred, because the Doge served as a literal embodiment of the idealisation of the reality of Venetian politics. For Contarini, this duality almost defines the greatness of the Venetian constitution. The Doge is the “heart”, under which “all are comprised”. Contarini places him in the centre of his body metaphor, making him synecdochical for the city and the people that reside within it. This means he is to ensure that the disparate, competing interests of the city beat in time with one another, creating in the process the “perfection of civil agreement”. His job as a conductor, rather than a ruler, means therefore that the role takes on the aspect of representative of the entire city. Contarini's description of his vestments, privileges and rituals can therefore be compared to Marin Sanudo’s description of the physical spaces of Venice in his essay In Praise of Venice. Both are designed to extol the virtues of the entire city by describing representative parts. This is apparent in the way both authors treat the chapel of St. Mark. Patron saints were hugely important in terms of civic self-identification in renaissance Italy. Contarini emphasizes this, saying that he is “with exceeding honour solemnized of the Venetians”. His description of the Doge's close relationship with the saint, through the “solemn pomp” with which he attends mass at the saint's chapel, attaches him to the aforementioned “exceeding honour”, in a similar fashion to the way in which Sanudo glorifies Venice as a whole by constantly referring to the beauty and worth of St. Mark's square and chapel as part of his panoramic praise of the city.

At the same time, however, Contarini's overall purpose is, of course, the glorification of the republican nature of his city. Therefore, he cannot avoid referring to “the other side” of the Doge's figure when discussing his “royal appearing show”. Things like the “kingly ornaments” which were “always purple garments or cloth of gold”, both very ostentatious assertions of wealth and power, were to ensure he was “recompensed” for his “limitation of authority”. Contarini thus openly concludes that the Doge is a combination of myth and reality, saying that “in everything you may see the show of a king, but his authority is nothing”. Indeed, as Edward Muir points out, “by the sixteenth century virtually every word, gesture and act that the doge made in public was subject to legal and ceremonial regulation”. He could not buy expensive jewels, own property outside Venice or the Veneto, display his insignia outside the Ducal Palace, decorate his apartment as he wanted, receive people in his ducal dress, send official letters, or have close ties with guilds, amongst a great many other restrictions. Legally, therefore, power in Venice came from the numerous councils, not the figurehead. The Doge thus becomes a brazen republican statement. Venice drew attention to a princely, magnificently adorned figurehead, only to direct most executive power to councils of her citizens.

title: Gasparo Contarini