Editing Radiometric dating (section)

==Modern dating methods==
Radiometric dating has been carried out since 1905 when it was [[Age of the Earth#Invention of radiometric dating|invented]] by [[Ernest Rutherford]] as a method by which one might determine the [[age of the Earth]]. In the century since then the techniques have been greatly improved and expanded.<ref name=usgs/> Dating can now be performed on samples as small as a nanogram using a [[mass spectrometer]]. The mass spectrometer was invented in the 1940s and began to be used in radiometric dating in the 1950s. It operates by generating a beam of [[ion|ionized atoms]] from the sample under test. The ions then travel through a magnetic field, which diverts them into different sampling sensors, known as "[[Faraday cup]]s," depending on their mass and level of ionization. On impact in the cups, the ions set up a very weak current that can be measured to determine the rate of impacts and the relative concentrations of different atoms in the beams.{{Citation needed|date=October 2022}}

===Uranium–lead dating method===
{{Main|Uranium–lead dating}}
[[File:Pfunze belt concordia.png|class=skin-invert-image|thumb|upright=1.8|A concordia diagram as used in [[uranium–lead dating]], with data from the [[Pfunze Belt]], [[Zimbabwe]].<ref>{{cite journal|doi=10.1016/S0899-5362(01)90021-1 |title=U–Pb zircon ages from a craton-margin archaean orogenic belt in northern Zimbabwe |year=2001 |first=M. L. |last=Vinyu |author2=R. E. Hanson |author3=M. W. Martin |author4=S. A. Bowring |author5=H. A. Jelsma |author6=P. H. G. M. Dirks |journal=[[Journal of African Earth Sciences]] |volume=32|issue=1 |pages=103–114|bibcode = 2001JAfES..32..103V }}</ref> All the samples show loss of lead isotopes, but the intercept of the errorchron (straight line through the sample points) and the concordia (curve) shows the correct age of the rock.<ref name=Rollinson/>]]

[[Uranium–lead radiometric dating]] involves using uranium-235 or uranium-238 to date a substance's absolute age. This scheme has been refined to the point that the error margin in dates of rocks can be as low as less than two million years in two-and-a-half billion years.<ref name="Oberthuer">{{cite journal|year=2002|title=Precise U–Pb mineral ages, Rb–Sr and Sm–Nd systematics for the Great Dyke, Zimbabwe—constraints on late Archean events in the Zimbabwe craton and Limpopo belt|journal=Precambrian Research|volume=113|issue=3–4|pages=293–306|bibcode=2002PreR..113..293O|doi=10.1016/S0301-9268(01)00215-7|last1=Oberthür |first1=Thomas |last2=Davis |first2=Donald W. |last3=Blenkinsop |first3=Thomas G. |last4=Höhndorf |first4=Axel }}</ref><ref>{{cite journal|doi=10.1016/j.jafrearsci.2004.12.003 |title=The age and petrology of the Chimbadzi Hill Intrusion, NW Zimbabwe: first evidence for early Paleoproterozoic magmatism in Zimbabwe |year=2004 |first=Tawanda D. |last=Manyeruke |author2=Thomas G. Blenkinsop |author3=Peter Buchholz |author4=David Love |author5=Thomas Oberthür |author6=Ulrich K. Vetter |author7=Donald W. Davis |journal=Journal of African Earth Sciences |volume=40|issue=5 |pages=281–292|bibcode = 2004JAfES..40..281M }}</ref> An error margin of 2–5% has been achieved on younger [[Mesozoic]] rocks.<ref>{{cite journal|doi=10.1016/S0009-2541(00)00394-6 |title=Precise <sup>206</sup>Pb/<sup>238</sup>U age determination on zircons by laser ablation microprobe-inductively coupled plasma-mass spectrometry using continuous linear ablation |year=2001 |first1=Xian-hua |last1=Li |first2=Xi-rong|last2=Liang|first3=Min|last3=Sun|first4=Hong|last4=Guan|first5=J. G.|last5=Malpas |journal=Chemical Geology |volume=175|issue=3–4 |pages=209–219|bibcode=2001ChGeo.175..209L}}</ref>

Uranium–lead dating is often performed on the [[mineral]] [[zircon]] (ZrSiO<sub>4</sub>), though it can be used on other materials, such as [[baddeleyite]] and [[monazite]] (see: [[monazite geochronology]]).<ref>{{cite journal|doi=10.2113/104.1.13 |title=SHRIMP baddeleyite and zircon ages for an Umkondo dolerite sill, Nyanga Mountains, Eastern Zimbabwe |year=2001 |first=M.T.D. |last=Wingate |journal=South African Journal of Geology |volume=104|issue=1 |pages=13–22|bibcode=2001SAJG..104...13W }}</ref> Zircon and baddeleyite incorporate uranium atoms into their crystalline structure as substitutes for [[zirconium]], but strongly reject lead. Zircon has a very high closure temperature, is resistant to mechanical weathering and is very chemically inert. Zircon also forms multiple crystal layers during metamorphic events, which each may record an isotopic age of the event. ''In situ'' micro-beam analysis can be achieved via laser [[ICP-MS]] or [[Secondary ion mass spectrometry|SIMS]] techniques.<ref>{{cite journal|doi=10.1126/science.286.5448.2289 |title=Isotope Geochemistry: New Tools for Isotopic Analysis |date=December 1999 |first=Trevor |last=Ireland |journal=Science |volume=286 |issue=5448 |pages=2289–2290|s2cid=129408440 }}</ref>

One of its great advantages is that any sample provides two clocks, one based on uranium-235's decay to lead-207 with a half-life of about 700 million years, and one based on uranium-238's decay to lead-206 with a half-life of about 4.5 billion years, providing a built-in crosscheck that allows accurate determination of the age of the sample even if some of the lead has been lost. This can be seen in the concordia diagram, where the samples plot along an errorchron (straight line) which intersects the concordia curve at the age of the sample.{{Citation needed|date=October 2022}}

===Samarium–neodymium dating method===
{{Main|Samarium–neodymium dating}}

This involves the [[alpha decay]] of <sup>147</sup>Sm to <sup>143</sup>Nd with a [[half-life]] of 1.06 x 10<sup>11</sup> years. Accuracy levels of within twenty million years in ages of two-and-a-half billion years are achievable.<ref>{{cite journal|doi=10.1016/S0012-821X(98)00228-3 |title=A multielement geochronologic study of the Great Dyke, Zimbabwe: significance of the robust and reset ages |date=December 1998 |first=S. B. |last=Mukasa |author2=A. H. Wilson |author3=R. W. Carlson |journal=Earth and Planetary Science Letters |volume=164 |issue=1–2 |pages=353–369 |bibcode=1998E&PSL.164..353M}}</ref>

===Potassium–argon dating method===
{{Main|Potassium–argon dating}}

This involves [[electron capture]] or [[positron]] decay of potassium-40 to argon-40. Potassium-40 has a half-life of 1.3 billion years, so this method is applicable to the oldest rocks. Radioactive potassium-40 is common in [[mica]]s, [[feldspar]]s, and [[hornblende]]s, though the closure temperature is fairly low in these materials, about 350&nbsp;°C (mica) to 500&nbsp;°C (hornblende).{{Citation needed|date=October 2022}}

===Rubidium–strontium dating method===
{{Main|Rubidium–strontium dating}}

This is based on the beta decay of [[rubidium-87]] to [[strontium-87]], with a half-life of 50 billion years. This scheme is used to date old [[igneous rock|igneous]] and [[metamorphic rock]]s, and has also been used to date [[moon rock|lunar samples]]. Closure temperatures are so high that they are not a concern. Rubidium-strontium dating is not as precise as the uranium–lead method, with errors of 30 to 50 million years for a 3-billion-year-old sample. Application of in situ analysis (Laser-Ablation ICP-MS) within single mineral grains in faults have shown that the Rb-Sr method can be used to decipher episodes of fault movement.<ref>{{cite journal|doi=10.1038/s41598-019-57262-5|title=In situ Rb-Sr dating of slickenfibres in deep crystalline basement faults |year=2020 |last1=Tillberg |first1=Mikael |last2=Drake |first2=Henrik |last3=Zack |first3=Thomas |last4=Kooijman |first4=Ellen |last5=Whitehouse |first5=Martin J. |last6=Åström |first6=Mats E. |journal=Scientific Reports |volume=10 |issue=1 |page=562 |pmid=31953465 |bibcode=2020NatSR..10..562T |s2cid=210670668 |pmc=6969261 }}</ref>

===Uranium–thorium dating method===
{{Main|Uranium–thorium dating}}

A relatively short-range dating technique is based on the decay of uranium-234 into thorium-230, a substance with a half-life of about 80,000 years. It is accompanied by a sister process, in which uranium-235 decays into protactinium-231, which has a half-life of 32,760 years.{{Citation needed|date=October 2022}}

While [[uranium]] is water-soluble, [[thorium]] and [[protactinium]] are not, and so they are selectively precipitated into ocean-floor [[sediment]]s, from which their ratios are measured. The scheme has a range of several hundred thousand years. A related method is [[ionium–thorium dating]], which measures the ratio of [[ionium]] (thorium-230) to thorium-232 in [[ocean sediment]].{{Citation needed|date=October 2022}}

===Radiocarbon dating method===
{{Main|Radiocarbon dating}}
[[File:Ales stenar bred.jpg|upright=1.35|thumb|right|[[Ale's Stones]] at Kåseberga, around ten kilometres south east of [[Ystad]], [[Sweden]] were dated back to approximately 1,400 years ago using the carbon-14 method on organic material found at the site.<ref>{{cite web |url=http://www.raa.se/cms/extern/en/places_to_visit/our_historical_sites/ales_stenar.html |title=Ales stenar |publisher=The Swedish National Heritage Board |date=11 October 2006 |access-date=9 March 2009 |url-status=dead |archive-url=https://web.archive.org/web/20090331132307/http://www.raa.se/cms/extern/en/places_to_visit/our_historical_sites/ales_stenar.html |archive-date=31 March 2009 }}</ref>]] [[Radiocarbon dating]] is also simply called carbon-14 dating. Carbon-14 is a radioactive isotope of carbon, with a half-life of 5,730 years<ref>{{cite journal|last=Clark |first=R. M. |year=1975 |title=A calibration curve for radiocarbon dates |journal=Antiquity |volume=49 |issue=196 |pages=251–266 |url=http://www.antiquity.ac.uk/ant/049/Ant0490251.htm|doi=10.1017/S0003598X00070277 |s2cid=161729853 }}</ref><ref>{{cite journal|doi=10.5194/angeo-20-115-2002 |first=S. S. |last=Vasiliev |author2=V. A. Dergachev |year=2002 |title=The ~2400-year cycle in atmospheric radiocarbon concentration: Bispectrum of <sup>14</sup>''C'' data over the last 8000 years |journal=Annales Geophysicae |volume=20|issue=1 |pages=115–120 |bibcode = 2002AnGeo..20..115V |url=http://hal.archives-ouvertes.fr/docs/00/31/69/27/PDF/angeo-20-115-2002.pdf |doi-access=free }}</ref> (which is very short compared with the above isotopes), and decays into nitrogen.<ref>{{cite web|url=http://www.chem.uwec.edu/Chem115_F00/nelsolar/chem.htm|title=Carbon-14 Dating|website=www.chem.uwec.edu|access-date=2016-04-06}}</ref> In other radiometric dating methods, the heavy parent isotopes were produced by [[nucleosynthesis]] in supernovas, meaning that any parent isotope with a short half-life should be extinct by now. Carbon-14, though, is continuously created through collisions of neutrons generated by [[cosmic rays]] with nitrogen in the [[upper atmosphere]] and thus remains at a near-constant level on Earth. The carbon-14 ends up as a trace component in atmospheric [[carbon dioxide]] (CO<sub>2</sub>).<ref>{{Cite web |date=2022-10-12 |title=How do we know the build-up of carbon dioxide in the atmosphere is caused by humans? {{!}} NOAA Climate.gov |url=https://www.climate.gov/news-features/climate-qa/how-do-we-know-build-carbon-dioxide-atmosphere-caused-humans |access-date=2024-10-21 |website=www.climate.gov |language=en}}</ref>

A carbon-based life form acquires carbon during its lifetime. Plants acquire it through [[photosynthesis]], and animals acquire it from consumption of plants and other animals. When an organism dies, it ceases to take in new carbon-14, and the existing isotope decays with a characteristic half-life (5730 years). The proportion of carbon-14 left when the remains of the organism are examined provides an indication of the time elapsed since its death. This makes carbon-14 an ideal dating method to date the age of bones or the remains of an organism. The carbon-14 dating limit lies around 58,000 to 62,000 years.<ref>{{cite journal|first=Wolfango |last=Plastino |author2=Lauri Kaihola |author3=Paolo Bartolomei |author4=Francesco Bella |year=2001 |title=Cosmic background reduction in the radiocarbon measurement by scintillation spectrometry at the underground laboratory of Gran Sasso |url=http://digitalcommons.library.arizona.edu/objectviewer?o=http%3A%2F%2Fradiocarbon.library.arizona.edu%2FVolume43%2FNumber2A%2Fazu_radiocarbon_v43_n2A_157_161_v.pdf |journal=Radiocarbon |volume=43 |issue=2A |pages=157–161|doi=10.1017/S0033822200037954 |doi-access=free }}</ref>

The rate of creation of carbon-14 appears to be roughly constant, as cross-checks of carbon-14 dating with other dating methods show it gives consistent results. However, local eruptions of [[volcano]]es or other events that give off large amounts of carbon dioxide can reduce local concentrations of carbon-14 and give inaccurate dates. The releases of carbon dioxide into the [[biosphere]] as a consequence of [[industrialization]] have also depressed the proportion of carbon-14 by a few percent; in contrast, the amount of carbon-14 was increased by above-ground [[nuclear bomb]] tests that were conducted into the early 1960s. Also, an increase in the [[solar wind]] or the Earth's [[magnetic field]] above the current value would depress the amount of carbon-14 created in the atmosphere.<ref>{{Cite journal |last1=Stuiver |first1=Minze |last2=Quay |first2=Paul D. |date=1980 |title=Changes in Atmospheric Carbon-14 Attributed to a Variable Sun |url=https://www.jstor.org/stable/1683178 |journal=Science |volume=207 |issue=4426 |pages=11–19 |doi=10.1126/science.207.4426.11 |jstor=1683178 |pmid=17730790 |bibcode=1980Sci...207...11S |issn=0036-8075}}</ref>

===Fission track dating method===
{{Main|fission track dating}}
[[File:Apatite Canada.jpg|thumb|[[Apatite]] crystals are widely used in fission track dating.]]
This involves inspection of a polished slice of a material to determine the density of "track" markings left in it by the [[spontaneous fission]] of uranium-238 impurities. The uranium content of the sample has to be known, but that can be determined by placing a plastic film over the polished slice of the material, and bombarding it with [[thermal neutrons|slow neutrons]]. This causes induced fission of <sup>235</sup>U, as opposed to the spontaneous fission of <sup>238</sup>U. The fission tracks produced by this process are recorded in the plastic film. The uranium content of the material can then be calculated from the number of tracks and the [[neutron flux]].<ref>{{Cite book |last1=Fleischer |first1=Robert L. |url=http://www.jstor.org/stable/jj.13167934 |title=Nuclear Tracks in Solids: Principles and Applications |last2=Price |first2=P. Buford |last3=Walker |first3=Robert M. |date=2024-03-29 |publisher=University of California Press |isbn=978-0-520-32023-9 |edition=1 |doi=10.2307/jj.13167934}}</ref>

This scheme has application over a wide range of geologic dates. For dates up to a few million years [[mica]]s, [[tektite]]s (glass fragments from volcanic eruptions), and meteorites are best used. Older materials can be dated using [[zircon]], [[apatite]], [[titanite]], [[epidote]] and [[garnet]] which have a variable amount of uranium content.<ref>{{cite journal|doi=10.1016/S0899-5362(01)80066-X |title=A titanite fission track profile across the southeastern Archæan Kaapvaal Craton and the Mesoproterozoic Natal Metamorphic Province, South Africa: evidence for differential cryptic Meso- to Neoproterozoic tectonism |date=August 2001 |first=J. |last=Jacobs |author2=R. J. Thomas |journal=Journal of African Earth Sciences |volume=33 |issue=2 |pages=323–333|bibcode = 2001JAfES..33..323J }}</ref> Because the fission tracks are healed by temperatures over about 200&nbsp;°C the technique has limitations as well as benefits. The technique has potential applications for detailing the thermal history of a deposit.<ref name="Naeser-McCulloh1989">{{cite book |last1=Naeser |first1=Nancy |last2=Naeser |first2=Charles |last3=McCulloh |first3=Thane |editor1-last=Naeser |editor1-first=Nancy |editor2-last=McCulloh |editor2-first=Thane |title=Thermal History of Sedimentary Basins |date=1989 |publisher=Springer New York|isbn=978-1-4612-8124-5|pages=157–180|chapter=The Application of Fission-Track Dating to the Depositional and Thermal History of Rocks in Sedimentary Basins|doi=10.1007/978-1-4612-3492-0_10 |chapter-url=https://link.springer.com/chapter/10.1007/978-1-4612-3492-0_10}}</ref>

===Chlorine-36 dating method===
Large amounts of otherwise rare [[chlorine-36|<sup>36</sup>Cl]] (half-life ~300ky) were produced by irradiation of seawater during atmospheric detonations of [[nuclear weapon]]s between 1952 and 1958. The residence time of <sup>36</sup>Cl in the atmosphere is about 1 week. Thus, as an event marker of 1950s water in soil and ground water, <sup>36</sup>Cl is also useful for dating waters less than 50 years before the present. <sup>36</sup>Cl has seen use in other areas of the geological sciences, including dating ice<ref>{{cite journal|last=Willerslev |first=E. |year=2007 |title=Ancient biomolecules from deep ice cores reveal a forested southern Greenland |journal=Science |volume=317 |issue=5834 |pages=111–114 |doi=10.1126/science.1141758|pmid=17615355 |pmc=2694912 |bibcode=2007Sci...317..111W |s2cid=7423309 }}</ref> and sediments.

===Luminescence dating methods===
{{Main|Luminescence dating}}

Luminescence dating methods are not radiometric dating methods in that they do not rely on abundances of isotopes to calculate age. Instead, they are a consequence of [[background radiation]] on certain minerals. Over time, [[ionizing radiation]] is absorbed by mineral grains in sediments and archaeological materials such as [[quartz]] and [[potassium feldspar]]. The radiation causes charge to remain within the grains in structurally unstable "electron traps". Exposure to sunlight or heat releases these charges, effectively "bleaching" the sample and resetting the clock to zero. The trapped charge accumulates over time at a rate determined by the amount of background radiation at the location where the sample was buried. Stimulating these mineral grains using either light ([[optically stimulated luminescence]] or infrared stimulated luminescence dating) or heat ([[thermoluminescence dating]]) causes a luminescence signal to be emitted as the stored unstable electron energy is released, the intensity of which varies depending on the amount of radiation absorbed during burial and specific properties of the mineral.<ref>{{Cite journal |last1=Roberts |first1=Richard G. |last2=Jacobs |first2=Zenobia |last3=Li |first3=Bo |last4=Jankowski |first4=Nathan R. |last5=Cunningham |first5=Alastair C. |last6=Rosenfeld |first6=Anatoly B. |date=2015-04-01 |title=Optical dating in archaeology: thirty years in retrospect and grand challenges for the future |url=https://linkinghub.elsevier.com/retrieve/pii/S0305440315000667 |journal=Journal of Archaeological Science |series=Scoping the Future of Archaeological Science: Papers in Honour of Richard Klein |volume=56 |pages=41–60 |doi=10.1016/j.jas.2015.02.028 |bibcode=2015JArSc..56...41R |issn=0305-4403}}</ref>

These methods can be used to date the age of a sediment layer, as layers deposited on top would prevent the grains from being "bleached" and reset by sunlight. Pottery shards can be dated to the last time they experienced significant heat, generally when they were fired in a kiln.<ref>{{Cite journal |last1=Roberts |first1=Richard G. |last2=Jacobs |first2=Zenobia |last3=Li |first3=Bo |last4=Jankowski |first4=Nathan R. |last5=Cunningham |first5=Alastair C. |last6=Rosenfeld |first6=Anatoly B. |date=2015-04-01 |title=Optical dating in archaeology: thirty years in retrospect and grand challenges for the future |url=https://linkinghub.elsevier.com/retrieve/pii/S0305440315000667 |journal=Journal of Archaeological Science |series=Scoping the Future of Archaeological Science: Papers in Honour of Richard Klein |volume=56 |pages=41–60 |doi=10.1016/j.jas.2015.02.028 |bibcode=2015JArSc..56...41R |issn=0305-4403}}</ref>

===Other methods===
Other methods include:{{Citation needed|date=October 2022}}
* [[Argon–argon dating|Argon–argon]] (Ar–Ar)
* [[Iodine–xenon dating|Iodine–xenon]] (I–Xe)
* [[Lanthanum–barium dating|Lanthanum–barium]] (La–Ba)
* [[Lead–lead dating|Lead–lead]] (Pb–Pb)
* [[Lutetium–hafnium dating|Lutetium–hafnium]] (Lu–Hf)
* [[Hafnium–tungsten dating]] (Hf-W)
* [[K–Ca dating|Potassium–calcium]] (K–Ca)
* [[Rhenium–osmium dating|Rhenium–osmium]] (Re–Os)
* [[Uranium–uranium dating|Uranium–uranium]] (U–U)
* [[Krypton–krypton dating|Krypton–krypton]] (Kr–Kr)
* [[Beryllium#Isotopes and nucleosynthesis|Beryllium]] (<sup>10</sup>Be–<sup>9</sup>Be)<ref>Application of the authigenic 10 Be/ 9 Be dating method to Late
Miocene–Pliocene sequences in the northern Danube Basin;Michal Šujan – Global and Planetary Change 137 (2016) 35–53; [https://www.researchgate.net/profile/Michal_Sujan/publication/287807148_Application_of_the_authigenic_10Be9Be_dating_method_to_Late_Miocene-Pliocene_sequences_in_the_northern_Danube_Basin_Pannonian_Basin_System_Confirmation_of_heterochronous_evolution_of_sedimentary_envir/links/5684144b08ae1e63f1f1c4c8/Application-of-the-authigenic-10Be-9Be-dating-method-to-Late-Miocene-Pliocene-sequences-in-the-northern-Danube-Basin-Pannonian-Basin-System-Confirmation-of-heterochronous-evolution-of-sedimentary-envi.pdf pdf]</ref>