Editing Geologic time scale (section)

== History of the geologic time scale ==
{{See also|History of geology|History of paleontology}}

=== Early history ===
The most modern geological time scale was not formulated until 1911<ref name="Holmes_19113">{{Cite journal |last1=Holmes |first1=Arthur |date=1911-06-09 |title=The association of lead with uranium in rock-minerals, and its application to the measurement of geological time |journal=Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character |volume=85 |issue=578 |pages=248–256 |bibcode=1911RSPSA..85..248H |doi=10.1098/rspa.1911.0036 |issn=0950-1207 |doi-access=free}}</ref> 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.<ref>{{Cite web |title=James Hutton {{!}} Father of Modern Geology, Scottish Naturalist {{!}} Britannica |url=https://www.britannica.com/biography/James-Hutton |access-date=2024-12-03 |website=www.britannica.com |language=en}}</ref> The broader concept of the relation between rocks and time can be traced back to (at least) the [[philosopher]]s of [[Ancient Greece]] from 1200 BC to 600 AD. [[Xenophanes|Xenophanes of Colophon]] (c. 570–487&nbsp;[[Common era|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 [[Marine transgression|transgressed]] over the land and at other times had [[Marine regression|regressed]].<ref name="Fischer_20093">{{Cite journal |last1=Fischer |first1=Alfred G. |last2=Garrison |first2=Robert E. |date=2009 |title=The role of the Mediterranean region in the development of sedimentary geology: a historical overview |url=https://onlinelibrary.wiley.com/doi/10.1111/j.1365-3091.2008.01009.x |journal=Sedimentology |language=en |volume=56 |issue=1 |pages=3–41 |bibcode=2009Sedim..56....3F |doi=10.1111/j.1365-3091.2008.01009.x |s2cid=128604255}}</ref> This view was shared by a few of Xenophanes's scholars and those that followed, including [[Aristotle]] (384–322 BC) who (with additional observations) reasoned that the positions of land and sea had changed over long periods of time. The concept of [[deep time]] was also recognized by [[History of science and technology in China|Chinese naturalist]] [[Shen Kuo]]<ref name="Nathan 19953">{{Cite book |last=Sivin |first=Nathan |url=http://worldcat.org/oclc/956775994 |title=Science in ancient China: researches and reflections |date=1995 |publisher=Variorum |isbn=0-86078-492-4 |oclc=956775994}}</ref> (1031–1095) and [[Islam]]ic [[scientist]]-philosophers, notably the [[Brethren of Purity|Brothers of Purity]], who wrote on the processes of stratification over the passage of time in their [[Encyclopedia of the Brethren of Purity|treatises]].<ref name="Fischer_20093" /> Their work likely inspired that of the 11th-century [[Persians|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.<ref name="Fischer_20093" /> Avicenna also recognized fossils as "petrifications of the bodies of plants and animals",<ref name="Adams_19383">{{Cite book |last=Adams |first=Frank D. |url=http://worldcat.org/oclc/165626104 |title=The Birth and Development of the Geological Sciences |date=1938 |publisher=Williams & Wilkins |isbn=0-486-26372-X |oclc=165626104}}</ref> with the 13th-century [[Dominican Order|Dominican]] [[bishop]] [[Albertus Magnus]] (c. 1200–1280), who drew from [[Aristotle|Aristotle's]] natural philosophy, extending this into a theory of a petrifying fluid.<ref name="Johnson">{{Cite journal |last1=Johnson |first1=Chris |last2=Bentley |first2=Callan |last3=Panchuk |first3=Karla |last4=Affolter |first4=Matt |last5=Layou |first5=Karen |last6=Jaye |first6=Shelley |last7=Kohrs |first7=Russ |last8=Inkenbrandt |first8=Paul |last9=Mosher |first9=Cam |last10=Ricketts |first10=Brian |last11=Estrada |first11=Charlene |title=Geologic Time and Relative Dating |url=https://open.maricopa.edu/fallglg102/part/sedimentary-rocks-and-environments/ |journal=Maricopa Open Digital Press |language=en}}</ref> These works appeared to have little influence on [[scholar]]s in [[Middle Ages|Medieval Europe]] who looked to the [[Bible]] to explain the origins of fossils and sea-level changes, often attributing these to the '[[Genesis flood narrative|Deluge]]', including [[Restoro d'Arezzo|Ristoro d'Arezzo]] in 1282.<ref name="Fischer_20093" /> 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':<ref name="McCurdy_19383">{{Cite book |last=McCurdy |first=Edward |url=https://www.worldcat.org/search?q=no:2233803&qt=advanced&dblist=638 |title=The notebooks of Leonardo da Vinci |date=1938 |publisher=Reynal & Hitchcock |location=New York |language=English |oclc=2233803}}</ref><ref name="Fischer_20093" />

{{blockquote|text=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.}}
[[File:Sketch of the Succession pf Strata and their relative Altitudes.jpg|thumb|Sketch of the Succession of Strata and their Relative Altitudes (William Smith)]]
These views of da Vinci remained unpublished, and thus lacked influence at the time; however, questions of fossils and their significance were pursued and, while views against [[Genesis creation narrative|Genesis]] were not readily accepted and dissent from [[Religion|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.<ref name="Fischer_20093" /> 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."<ref name="Johnson" /> Later, in the 19th century, academics further developed theories on stratification. [[William Smith (geologist)|William Smith]], often referred to as the "Father of Geology"<ref name="earthobservatory.nasa.gov-2008" /> 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”.<ref name="earthobservatory.nasa.gov-2008">{{Cite web |date=2008-05-08 |title=William Smith (1769-1839) |url=https://earthobservatory.nasa.gov/features/WilliamSmith |access-date=2024-12-02 |website=earthobservatory.nasa.gov |language=en}}</ref> After studying rock layers and the fossils they contained, [[William Smith (geologist)|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.<ref name="Smith-1816">{{Cite book |last1=Smith |first1=William |url=https://www.biodiversitylibrary.org/bibliography/106808 |title=Strata identified by organized fossils : containing prints on colored paper of the most characteristic specimens in each stratum |last2=Smith |first2=William |date=1816 |publisher=Printed by W. Arding ..., and sold by the author ..., J. Sowerby ..., Sherwood, Neely, and Jones, and Longman, Hurst, Rees, Orme, and Brown ..., and by all booksellers |location=London |doi=10.5962/bhl.title.106808}}</ref> 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."<ref name="Smith-1816" />

=== 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.<ref name="Fischer_20093"/> In ''De solido intra solidum naturaliter contento dissertationis prodromus'' Steno states:<ref name="Steno_1669">{{Cite book |last=Steno |first=Nicolaus |url=https://books.google.com/books?id=xz28AAAAIAAJ |title=Nicolai Stenonis de solido intra solidvm natvraliter contento dissertationis prodromvs ad serenissimvm Ferdinandvm II ... |date=1669 |publisher=W. Junk |language=la}}</ref><ref name="Kardel_2018">{{Citation |last1=Kardel |first1=Troels |date=2018 |url=http://link.springer.com/10.1007/978-3-662-55047-2_38 |work=Nicolaus Steno |pages=763–825 |place=Berlin, Heidelberg |publisher=Springer Berlin Heidelberg |language=en |doi=10.1007/978-3-662-55047-2_38 |isbn=978-3-662-55046-5 |access-date=2022-04-20 |last2=Maquet |first2=Paul|title=2.27 the Prodromus to a Dissertation on a Solid Naturally Contained within a Solid }}</ref>
<blockquote>
* 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.
</blockquote>
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 myth|Creation]]). While Steno's principles were simple and attracted much attention, applying them proved challenging.<ref name="Fischer_20093"/> 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 (theologian)|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"''.<ref name="Burnet_1681">{{Cite book |last=Burnet |first=Thomas |title=Telluris Theoria Sacra: orbis nostri originen et mutationes generales, quasi am subiit aut olim subiturus est, complectens. Libri duo priores de Diluvio & Paradiso |publisher=G. Kettiby |year=1681 |location=London |language=la}}</ref><ref name="Fischer_20093"/> [[Anton Moro]] (1687–1784) also used primary and secondary divisions for rock units but his mechanism was volcanic.<ref name="Moro_1740">{{Cite book |last=Moro |first=Anton Lazzaro |url=https://books.google.com/books?id=03RBAAAAYAAJ |title=De'crostacei e degli altri marini corpi che si truovano su'monti |date=1740 |publisher=Appresso Stefano Monti |language=it}}</ref><ref name="Fischer_20093"/> 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 (geologist)|Giovanni Arduino]] (1713–1795) to include tertiary and quaternary divisions.<ref name="Fischer_20093"/> 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.<ref name="Hutton_1788">{{Cite journal |last=Hutton |first=James |date=1788 |title=X. Theory of the Earth; or an Investigation of the Laws observable in the Composition, Dissolution, and Restoration of Land upon the Globe . |url=https://www.cambridge.org/core/product/identifier/S0080456800029227/type/journal_article |journal=Transactions of the Royal Society of Edinburgh |language=en |volume=1 |issue=2 |pages=209–304 |doi=10.1017/S0080456800029227 |s2cid=251578886 |issn=0080-4568}}</ref><ref name="Hutton_1795v1">{{Cite book |last=Hutton |first=James |url=https://www.gutenberg.org/ebooks/12861 |title=Theory of the Earth |year=1795 |volume=1 |location=Edinburgh}}</ref><ref name="Hutton_1795v2">{{Cite book |last=Hutton |first=James |url=https://www.gutenberg.org/ebooks/14179 |title=Theory of the Earth |year=1795 |volume=2 |location=Edinburgh}}</ref> Hutton's theory would later become known as [[uniformitarianism]], popularised by [[John Playfair]]<ref name="Playfair_1802">{{Cite book |last=Playfair |first=John |url=http://archive.org/details/NHM104643 |title=Illustrations of the Huttonian theory of the earth |date=1802 |publisher=Neill & Co |others=Digitised by London Natural History Museum Library |location=Edinburgh}}</ref> (1748–1819) and later [[Charles Lyell]] (1797–1875) in his ''[[Principles of Geology]]''.<ref name="Lyell_1832v1">{{Cite book |last=Lyell |first=Sir Charles |url=https://books.google.com/books?id=mmIOAAAAQAAJ |title=Principles of Geology: Being an Attempt to Explain the Former Changes of the Earth's Surface, by Reference to Causes Now in Operation |date=1832 |publisher=John Murray |volume=1 |location=London |language=en}}</ref><ref name="Lyell_1832v2">{{Cite book |last=Lyell |first=Sir Charles |url=https://books.google.com/books?id=TlwPAAAAYAAJ |title=Principles of Geology: Being an Attempt to Explain the Former Changes of the Earth's Surface, by Reference to Causes Now in Operation |date=1832 |publisher=John Murray |volume=2 |location=London |language=en}}</ref><ref name="Lyell_1834v3">{{Cite book |last=Lyell |first=Sir Charles |url=https://books.google.com/books?id=UrIJAAAAIAAJ |title=Principles of Geology: Being an Inquiry how for the Former Changes of the Earth's Surface are Referrable to Causes Now in Operation |date=1834 |publisher=John Murray |volume=3 |location=London |language=en}}</ref> 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 (geologist)|William Smith]], [[Georges Cuvier]], [[Jean Baptiste Julien d'Omalius d'Halloy|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.<ref name="Dalrymple 2001 AoE" /> These estimations varied from 15,000 million years to 0.075 million years depending on method and author, but the estimations of [[William Thomson, 1st Baron Kelvin|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.<ref name="Dalrymple 2001 AoE" /> Early attempts at determining ages of uranium minerals and rocks by [[Ernest Rutherford]], [[Bertram Boltwood]], [[Robert Strutt, 4th Baron Rayleigh|Robert Strutt]], and Arthur Holmes, would culminate in what are considered the first international geological time scales by Holmes in 1911 and 1913.<ref name="Holmes_19113"/><ref name="Holmes 1913">{{Cite book |last=Holmes |first=Arthur |url=http://archive.org/details/ageofearth00holmuoft |title=The age of the earth |date=1913 |publisher=London, Harper |others=Gerstein - University of Toronto}}</ref><ref name="Lewis_2001">{{Cite journal |last=Lewis |first=Cherry L. E. |date=2001 |title=Arthur Holmes' vision of a geological timescale |url=http://sp.lyellcollection.org/lookup/doi/10.1144/GSL.SP.2001.190.01.10 |journal=Geological Society, London, Special Publications |language=en |volume=190 |issue=1 |pages=121–138 |doi=10.1144/GSL.SP.2001.190.01.10 |bibcode=2001GSLSP.190..121L |s2cid=128686640 |issn=0305-8719}}</ref> The discovery of [[isotope]]s in 1913<ref>{{Cite journal |last=Soddy |first=Frederick |date=1913-12-04 |title=Intra-atomic Charge |url=https://www.nature.com/articles/092399c0 |journal=Nature |language=en |volume=92 |issue=2301 |pages=399–400 |doi=10.1038/092399c0 |bibcode=1913Natur..92..399S |s2cid=3965303 |issn=0028-0836}}</ref> 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.<ref name="Dalrymple 2001 AoE" /><ref name="Lewis_2001" /><ref name="Holmes_1960">{{Cite journal |last=Holmes |first=A. |date=1959-01-01 |title=A revised geological time-scale |url=http://trned.lyellcollection.org/cgi/doi/10.1144/transed.17.3.183 |journal=Transactions of the Edinburgh Geological Society |language=en |volume=17 |issue=3 |pages=183–216 |doi=10.1144/transed.17.3.183 |s2cid=129166282 |issn=0371-6260}}</ref><ref name="GTS1960">{{Cite journal |date=1960 |title=A Revised Geological Time-Scale |journal=Nature |language=en |volume=187 |issue=4731 |pages=27–28 |doi=10.1038/187027d0 |bibcode=1960Natur.187T..27. |s2cid=4179334 |issn=0028-0836|doi-access=free }}</ref>

=== Modern international geological time scale ===
The establishment of the IUGS in 1961<ref name="Harrison_1978">{{Cite journal |last=Harrison |first=James M. |title=The Roots of IUGS |date=1978-03-01 |journal=Episodes |volume=1 |issue=1 |pages=20–23 |doi=10.18814/epiiugs/1978/v1i1/005 |issn=0705-3797|doi-access=free }}</ref> and acceptance of the Commission on Stratigraphy (applied in 1965)<ref name="ICS_statutes_1986">{{Cite book |author=International Union of Geological Sciences. Commission on Stratigraphy |url=https://www.worldcat.org/oclc/14352783 |title=Guidelines and statutes of the International Commission on Stratigraphy (ICS) |date=1986 |publisher=Herausgegeben von der Senckenbergischen Naturforschenden Gesellschaft |others=J. W. Cowie |isbn=3-924500-19-3 |location=Frankfurt a.M. |oclc=14352783}}</ref> 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".<ref name="ICS_statutes" />

Following on from Holmes, several ''A Geological Time Scale'' books were published in 1982,<ref name="GTS82">{{Cite book |url=https://www.worldcat.org/oclc/8387993 |title=A geologic time scale |date=1982 |publisher=Cambridge University Press |author=W. B. Harland |isbn=0-521-24728-4 |location=Cambridge [England] |oclc=8387993}}</ref> 1989,<ref name="GTS1989">{{Cite book |url=https://www.worldcat.org/oclc/20930970 |title=A geologic time scale 1989 |date=1990 |publisher=Cambridge University Press |author=W. B. Harland |isbn=0-521-38361-7 |location=Cambridge |oclc=20930970}}</ref> 2004,<ref name="GTS2004">{{Cite book |url=https://www.worldcat.org/oclc/60770922 |title=A geologic time scale 2004 |date=2004 |publisher=Cambridge University Press |author1=F. M. Gradstein |author2=James G. Ogg |author3=A. Gilbert Smith |isbn=0-511-08201-0 |location=Cambridge, UK |oclc=60770922}}</ref> 2008,<ref name="GTS2008">{{Cite journal |last1=Gradstein |first1=Felix M. |last2=Ogg |first2=James G. |last3=van Kranendonk |first3=Martin |date=2008-07-23 |title=On the Geologic Time Scale 2008 |url=http://www.schweizerbart.de/papers/nos/detail/43/63825/On_the_Geologic_Time_Scale_2008?af=crossref |journal=Newsletters on Stratigraphy |language=en |volume=43 |issue=1 |pages=5–13 |doi=10.1127/0078-0421/2008/0043-0005 |issn=0078-0421}}</ref> 2012,<ref name="GTS2012">{{Cite book |url=https://www.worldcat.org/oclc/808340848 |title=The geologic time scale 2012. Volume 2 |date=2012 |publisher=Elsevier |author=F. M. Gradstein |isbn=978-0-444-59448-8 |edition=1st |location=Amsterdam |oclc=808340848}}</ref> 2016,<ref name="GTS2016">{{Cite book |last=Ogg |first=James G. |url=https://www.worldcat.org/oclc/949988705 |title=A concise geologic time scale 2016 |date=2016 |publisher=Elsevier |others=Gabi Ogg, F. M. Gradstein |isbn=978-0-444-59468-6 |location=Amsterdam, Netherlands |oclc=949988705}}</ref> and 2020.<ref name="GTS2020">{{Cite book |url=https://www.worldcat.org/oclc/1224105111 |title=Geologic time scale 2020 |date=2020 |author1=F. M. Gradstein |author2=James G. Ogg |author3=Mark D. Schmitz |author4=Gabi Ogg |isbn=978-0-12-824361-9 |location=Amsterdam, Netherlands |oclc=1224105111}}</ref> 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.<ref name="ICC_Cohen_2013" /> Subsequent ''Geologic Time Scale'' books (2016<ref name="GTS2016" /> and 2020<ref name="GTS2020"/>) 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.

{{Timeline geological timescale}}