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Geochronology

Geochronology is the science of determining the age of rocks, fossils, and sediments using signatures inherent in the rocks themselves. Absolute geochronology can be accomplished through radioactive isotopes, whereas relative geochronology is provided by tools such as paleomagnetism and stable isotope ratios. By combining multiple geochronological (and biostratigraphic) indicators the precision of the recovered age can be improved.

An artistic depiction of the major events in the history of Earth

Geochronology is different in application from biostratigraphy, which is the science of assigning sedimentary rocks to a known geological period via describing, cataloging and comparing fossil floral and faunal assemblages. Biostratigraphy does not directly provide an absolute age determination of a rock, but merely places it within an interval of time at which that fossil assemblage is known to have coexisted. Both disciplines work together hand in hand, however, to the point where they share the same system of naming strata (rock layers) and the time spans utilized to classify sublayers within a stratum.

The science of geochronology is the prime tool used in the discipline of chronostratigraphy, which attempts to derive absolute age dates for all fossil assemblages and determine the geologic history of the Earth and extraterrestrial bodies.

Dating methods Edit

Units in geochronology and stratigraphy[1]
Segments of rock (strata) in chronostratigraphy Time spans in geochronology Notes to
geochronological units
Eonothem Eon 4 total, half a billion years or more
Erathem Era 10 defined, several hundred million years
System Period 22 defined, tens to ~one hundred million years
Series Epoch 34 defined, tens of millions of years
Stage Age 99 defined, millions of years
Chronozone Chron subdivision of an age, not used by the ICS timescale

Radiometric dating Edit

By measuring the amount of radioactive decay of a radioactive isotope with a known half-life, geologists can establish the absolute age of the parent material. A number of radioactive isotopes are used for this purpose, and depending on the rate of decay, are used for dating different geological periods. More slowly decaying isotopes are useful for longer periods of time, but less accurate in absolute years. With the exception of the radiocarbon method, most of these techniques are actually based on measuring an increase in the abundance of a radiogenic isotope, which is the decay-product of the radioactive parent isotope.[2][3][4] Two or more radiometric methods can be used in concert to achieve more robust results.[5] Most radiometric methods are suitable for geological time only, but some such as the radiocarbon method and the 40Ar/39Ar dating method can be extended into the time of early human life[6] and into recorded history.[7]

Some of the commonly used techniques are:

Fission-track dating Edit

Cosmogenic nuclide geochronology Edit

A series of related techniques for determining the age at which a geomorphic surface was created (exposure dating), or at which formerly surficial materials were buried (burial dating).[10] Exposure dating uses the concentration of exotic nuclides (e.g. 10Be, 26Al, 36Cl) produced by cosmic rays interacting with Earth materials as a proxy for the age at which a surface, such as an alluvial fan, was created. Burial dating uses the differential radioactive decay of 2 cosmogenic elements as a proxy for the age at which a sediment was screened by burial from further cosmic rays exposure.

Luminescence dating Edit

Luminescence dating techniques observe 'light' emitted from materials such as quartz, diamond, feldspar, and calcite. Many types of luminescence techniques are utilized in geology, including optically stimulated luminescence (OSL), cathodoluminescence (CL), and thermoluminescence (TL).[11] Thermoluminescence and optically stimulated luminescence are used in archaeology to date 'fired' objects such as pottery or cooking stones and can be used to observe sand migration.

Incremental dating Edit

Incremental dating techniques allow the construction of year-by-year annual chronologies, which can be fixed (i.e. linked to the present day and thus calendar or sidereal time) or floating.

Paleomagnetic dating Edit

A sequence of paleomagnetic poles (usually called virtual geomagnetic poles), which are already well defined in age, constitutes an apparent polar wander path (APWP). Such a path is constructed for a large continental block. APWPs for different continents can be used as a reference for newly obtained poles for the rocks with unknown age. For paleomagnetic dating, it is suggested to use the APWP in order to date a pole obtained from rocks or sediments of unknown age by linking the paleopole to the nearest point on the APWP. Two methods of paleomagnetic dating have been suggested: (1) the angular method and (2) the rotation method.[12] The first method is used for paleomagnetic dating of rocks inside of the same continental block. The second method is used for the folded areas where tectonic rotations are possible.

Magnetostratigraphy Edit

Magnetostratigraphy determines age from the pattern of magnetic polarity zones in a series of bedded sedimentary and/or volcanic rocks by comparison to the magnetic polarity timescale. The polarity timescale has been previously determined by dating of seafloor magnetic anomalies, radiometrically dating volcanic rocks within magnetostratigraphic sections, and astronomically dating magnetostratigraphic sections.

Chemostratigraphy Edit

Global trends in isotope compositions, particularly carbon-13 and strontium isotopes, can be used to correlate strata.[13]

Correlation of marker horizons Edit

 
Tephra horizons in south-central Iceland. The thick and light-to-dark coloured layer at the height of the volcanologist's hands is a marker horizon of rhyolitic-to-basaltic tephra from Hekla.

Marker horizons are stratigraphic units of the same age and of such distinctive composition and appearance that, despite their presence in different geographic sites, there is certainty about their age-equivalence. Fossil faunal and floral assemblages, both marine and terrestrial, make for distinctive marker horizons.[14] Tephrochronology is a method for geochemical correlation of unknown volcanic ash (tephra) to geochemically fingerprinted, dated tephra. Tephra is also often used as a dating tool in archaeology, since the dates of some eruptions are well-established.

Geological hierarchy of chronological periodization Edit

Geochronology, from largest to smallest:

  1. Supereon
  2. Eon
  3. Era
  4. Period
  5. Epoch
  6. Age
  7. Chron

Differences from chronostratigraphy Edit

It is important not to confuse geochronologic and chronostratigraphic units.[15] Geochronological units are periods of time, thus it is correct to say that Tyrannosaurus rex lived during the Late Cretaceous Epoch.[16] Chronostratigraphic units are geological material, so it is also correct to say that fossils of the genus Tyrannosaurus have been found in the Upper Cretaceous Series.[17] In the same way, it is entirely possible to go and visit an Upper Cretaceous Series deposit – such as the Hell Creek deposit where the Tyrannosaurus fossils were found – but it is naturally impossible to visit the Late Cretaceous Epoch as that is a period of time.

See also Edit

References Edit

  1. ^ Cohen, K.M.; Finney, S.; Gibbard, P.L. (2015), International Chronostratigraphic Chart (PDF), International Commission on Stratigraphy.
  2. ^ Dickin, A. P. 1995. Radiogenic Isotope Geology. Cambridge, Cambridge University Press. ISBN 0-521-59891-5
  3. ^ Faure, G. 1986. Principles of isotope geology. Cambridge, Cambridge University Press. ISBN 0-471-86412-9
  4. ^ Faure, G., and Mensing, D. 2005. "Isotopes - Principles and applications". 3rd Edition. J. Wiley & Sons. ISBN 0-471-38437-2
  5. ^ Dalrymple, G. B.; Grove, M.; Lovera, O. M.; Harrison, T. M.; Hulen, J. B.; Lanphere, M. A. (1999). "Age and thermal history of the Geysers plutonic complex (felsite unit), Geysers geothermal field, California: a 40Ar/39Ar and U–Pb study". Earth and Planetary Science Letters. 173 (3): 285–298. Bibcode:1999E&PSL.173..285D. doi:10.1016/S0012-821X(99)00223-X.
  6. ^ Ludwig, K. R.; Renne, P. R. (2000). "Geochronology on the Paleoanthropological Time Scale". Evolutionary Anthropology. 9 (2): 101–110. doi:10.1002/(sici)1520-6505(2000)9:2<101::aid-evan4>3.0.co;2-w. S2CID 83948790. Archived from the original on 2013-01-05.
  7. ^ Renne, P. R., Sharp, W. D., Deino. A. L., Orsi, G., and Civetta, L. 1997. Science, 277, 1279-1280 (PDF). Archived from the original (PDF) on 2008-10-30. Retrieved 2008-10-25.
  8. ^ Plastino, W.; Kaihola, L.; Bartolomei, P.; Bella, F. (2001). "Cosmic Background Reduction In The Radiocarbon Measurement By Scintillation Spectrometry At The Underground Laboratory Of Gran Sasso". Radiocarbon. 43 (2A): 157–161. doi:10.1017/S0033822200037954.
  9. ^ Hajdas, Irka; Ascough, Philippa; Garnett, Mark H.; Fallon, Stewart J.; Pearson, Charlotte L.; Quarta, Gianluca; Spalding, Kirsty L.; Yamaguchi, Haruka; Yoneda, Minoru (2021-09-09). "Radiocarbon dating". Nature Reviews Methods Primers. 1 (1): 1–26. doi:10.1038/s43586-021-00058-7. ISSN 2662-8449.
  10. ^ Schaefer, Joerg M.; Codilean, Alexandru T.; Willenbring, Jane K.; Lu, Zheng-Tian; Keisling, Benjamin; Fülöp, Réka-H.; Val, Pedro (2022-03-10). "Cosmogenic nuclide techniques". Nature Reviews Methods Primers. 2 (1): 1–22. doi:10.1038/s43586-022-00096-9. ISSN 2662-8449. S2CID 247396585.
  11. ^ Murray, Andrew; Arnold, Lee J.; Buylaert, Jan-Pieter; Guérin, Guillaume; Qin, Jintang; Singhvi, Ashok K.; Smedley, Rachel; Thomsen, Kristina J. (2021-10-28). "Optically stimulated luminescence dating using quartz". Nature Reviews Methods Primers. 1 (1): 1–31. doi:10.1038/s43586-021-00068-5. ISSN 2662-8449. S2CID 240186965.
  12. ^ Hnatyshin, D., and Kravchinsky, V.A., 2014. Paleomagnetic dating: Methods, MATLAB software, example. Tectonophysics, doi: 10.1016/j.tecto.2014.05.013 [1]
  13. ^ Brasier, M D; Sukhov, S S (1 April 1998). "The falling amplitude of carbon isotopic oscillations through the Lower to Middle Cambrian: northern Siberia data". Canadian Journal of Earth Sciences. 35 (4): 353–373. Bibcode:1998CaJES..35..353B. doi:10.1139/e97-122.
  14. ^ Demidov, I.N. (2006). "Identification of marker horizon in bottom sediments of the Onega Periglacial Lake". Doklady Earth Sciences. 407 (1): 213–216. Bibcode:2006DokES.407..213D. doi:10.1134/S1028334X06020127. S2CID 140634223.
  15. ^ David Weishampel: The Evolution and Extinction of the Dinosaurs, 1996, Cambridge Press, ISBN 0-521-44496-9
  16. ^ Julia Jackson: Glossary of Geology, 1987, American Geological Institute, ISBN 0-922152-34-9
  17. ^ Smith, J.B.; Lamanna, M.C.; Lacovara, K.J.; Dodson, Poole; Jnr, P.; Giegengack, R. (2001). "A Giant Sauropod Dinosaur from an Upper Cretaceous Mangrove Deposit in Egypt" (PDF). Science. 292 (5522): 1704–1707. Bibcode:2001Sci...292.1704S. doi:10.1126/science.1060561. PMID 11387472. S2CID 33454060.

Further reading Edit

  • Smart, P.L., and Frances, P.D. (1991), Quaternary dating methods - a user's guide. Quaternary Research Association Technical Guide No.4 ISBN 0-907780-08-3
  • Lowe, J.J., and Walker, M.J.C. (1997), Reconstructing Quaternary Environments (2nd edition). Longman publishing ISBN 0-582-10166-2
  • Mattinson, J. M. (2013), Revolution and evolution: 100 years of U-Pb geochronology. Elements 9, 53–57.
  • Geochronology bibliography Talk:Origins Archive

External links Edit

  • International Commission on Stratigraphy
  • BGS Open Data Geochronological Ontologies

geochronology, science, determining, rocks, fossils, sediments, using, signatures, inherent, rocks, themselves, absolute, geochronology, accomplished, through, radioactive, isotopes, whereas, relative, geochronology, provided, tools, such, paleomagnetism, stab. Geochronology is the science of determining the age of rocks fossils and sediments using signatures inherent in the rocks themselves Absolute geochronology can be accomplished through radioactive isotopes whereas relative geochronology is provided by tools such as paleomagnetism and stable isotope ratios By combining multiple geochronological and biostratigraphic indicators the precision of the recovered age can be improved An artistic depiction of the major events in the history of EarthGeochronology is different in application from biostratigraphy which is the science of assigning sedimentary rocks to a known geological period via describing cataloging and comparing fossil floral and faunal assemblages Biostratigraphy does not directly provide an absolute age determination of a rock but merely places it within an interval of time at which that fossil assemblage is known to have coexisted Both disciplines work together hand in hand however to the point where they share the same system of naming strata rock layers and the time spans utilized to classify sublayers within a stratum The science of geochronology is the prime tool used in the discipline of chronostratigraphy which attempts to derive absolute age dates for all fossil assemblages and determine the geologic history of the Earth and extraterrestrial bodies Contents 1 Dating methods 1 1 Radiometric dating 1 2 Fission track dating 1 3 Cosmogenic nuclide geochronology 1 4 Luminescence dating 1 5 Incremental dating 1 6 Paleomagnetic dating 1 7 Magnetostratigraphy 1 8 Chemostratigraphy 1 9 Correlation of marker horizons 2 Geological hierarchy of chronological periodization 3 Differences from chronostratigraphy 4 See also 5 References 6 Further reading 7 External linksDating methods EditUnits in geochronology and stratigraphy 1 Segments of rock strata in chronostratigraphy Time spans in geochronology Notes togeochronological unitsEonothem Eon 4 total half a billion years or moreErathem Era 10 defined several hundred million yearsSystem Period 22 defined tens to one hundred million yearsSeries Epoch 34 defined tens of millions of yearsStage Age 99 defined millions of yearsChronozone Chron subdivision of an age not used by the ICS timescaleRadiometric dating Edit Main article Radiometric dating By measuring the amount of radioactive decay of a radioactive isotope with a known half life geologists can establish the absolute age of the parent material A number of radioactive isotopes are used for this purpose and depending on the rate of decay are used for dating different geological periods More slowly decaying isotopes are useful for longer periods of time but less accurate in absolute years With the exception of the radiocarbon method most of these techniques are actually based on measuring an increase in the abundance of a radiogenic isotope which is the decay product of the radioactive parent isotope 2 3 4 Two or more radiometric methods can be used in concert to achieve more robust results 5 Most radiometric methods are suitable for geological time only but some such as the radiocarbon method and the 40Ar 39Ar dating method can be extended into the time of early human life 6 and into recorded history 7 Some of the commonly used techniques are Radiocarbon dating This technique measures the decay of carbon 14 in organic material and can be best applied to samples younger than about 60 000 years 8 9 Uranium lead dating This technique measures the ratio of two lead isotopes lead 206 and lead 207 to the amount of uranium in a mineral or rock Often applied to the trace mineral zircon in igneous rocks this method is one of the two most commonly used along with argon argon dating for geologic dating Monazite geochronology is another example of U Pb dating employed for dating metamorphism in particular Uranium lead dating is applied to samples older than about 1 million years Uranium thorium dating This technique is used to date speleothems corals carbonates and fossil bones Its range is from a few years to about 700 000 years Potassium argon dating and argon argon dating These techniques date metamorphic igneous and volcanic rocks They are also used to date volcanic ash layers within or overlying paleoanthropologic sites The younger limit of the argon argon method is a few thousand years Electron spin resonance ESR datingFission track dating Edit Main article Fission track dating Cosmogenic nuclide geochronology Edit Main article Cosmogenic radionuclide dating A series of related techniques for determining the age at which a geomorphic surface was created exposure dating or at which formerly surficial materials were buried burial dating 10 Exposure dating uses the concentration of exotic nuclides e g 10Be 26Al 36Cl produced by cosmic rays interacting with Earth materials as a proxy for the age at which a surface such as an alluvial fan was created Burial dating uses the differential radioactive decay of 2 cosmogenic elements as a proxy for the age at which a sediment was screened by burial from further cosmic rays exposure Luminescence dating Edit Luminescence dating techniques observe light emitted from materials such as quartz diamond feldspar and calcite Many types of luminescence techniques are utilized in geology including optically stimulated luminescence OSL cathodoluminescence CL and thermoluminescence TL 11 Thermoluminescence and optically stimulated luminescence are used in archaeology to date fired objects such as pottery or cooking stones and can be used to observe sand migration Incremental dating Edit Main article Incremental dating Incremental dating techniques allow the construction of year by year annual chronologies which can be fixed i e linked to the present day and thus calendar or sidereal time or floating Dendrochronology Ice cores Lichenometry VarvesPaleomagnetic dating Edit A sequence of paleomagnetic poles usually called virtual geomagnetic poles which are already well defined in age constitutes an apparent polar wander path APWP Such a path is constructed for a large continental block APWPs for different continents can be used as a reference for newly obtained poles for the rocks with unknown age For paleomagnetic dating it is suggested to use the APWP in order to date a pole obtained from rocks or sediments of unknown age by linking the paleopole to the nearest point on the APWP Two methods of paleomagnetic dating have been suggested 1 the angular method and 2 the rotation method 12 The first method is used for paleomagnetic dating of rocks inside of the same continental block The second method is used for the folded areas where tectonic rotations are possible Magnetostratigraphy Edit Main article Magnetostratigraphy Magnetostratigraphy determines age from the pattern of magnetic polarity zones in a series of bedded sedimentary and or volcanic rocks by comparison to the magnetic polarity timescale The polarity timescale has been previously determined by dating of seafloor magnetic anomalies radiometrically dating volcanic rocks within magnetostratigraphic sections and astronomically dating magnetostratigraphic sections Chemostratigraphy Edit Global trends in isotope compositions particularly carbon 13 and strontium isotopes can be used to correlate strata 13 Correlation of marker horizons Edit nbsp Tephra horizons in south central Iceland The thick and light to dark coloured layer at the height of the volcanologist s hands is a marker horizon of rhyolitic to basaltic tephra from Hekla Marker horizons are stratigraphic units of the same age and of such distinctive composition and appearance that despite their presence in different geographic sites there is certainty about their age equivalence Fossil faunal and floral assemblages both marine and terrestrial make for distinctive marker horizons 14 Tephrochronology is a method for geochemical correlation of unknown volcanic ash tephra to geochemically fingerprinted dated tephra Tephra is also often used as a dating tool in archaeology since the dates of some eruptions are well established Geological hierarchy of chronological periodization EditGeochronology from largest to smallest Supereon Eon Era Period Epoch Age ChronDifferences from chronostratigraphy EditIt is important not to confuse geochronologic and chronostratigraphic units 15 Geochronological units are periods of time thus it is correct to say that Tyrannosaurus rex lived during the Late Cretaceous Epoch 16 Chronostratigraphic units are geological material so it is also correct to say that fossils of the genus Tyrannosaurus have been found in the Upper Cretaceous Series 17 In the same way it is entirely possible to go and visit an Upper Cretaceous Series deposit such as the Hell Creek deposit where the Tyrannosaurus fossils were found but it is naturally impossible to visit the Late Cretaceous Epoch as that is a period of time See also EditAstronomical chronology Age of Earth Age of the universe Chronological dating archaeological chronology Absolute dating Relative dating Phase archaeology Archaeological association Geochronology Closure temperature Geologic time scale Geological history of Earth Thermochronology List of geochronologic names General Consilience evidence from independent unrelated sources can converge on strong conclusionsReferences Edit Cohen K M Finney S Gibbard P L 2015 International Chronostratigraphic Chart PDF International Commission on Stratigraphy Dickin A P 1995 Radiogenic Isotope Geology Cambridge Cambridge University Press ISBN 0 521 59891 5 Faure G 1986 Principles of isotope geology Cambridge Cambridge University Press ISBN 0 471 86412 9 Faure G and Mensing D 2005 Isotopes Principles and applications 3rd Edition J Wiley amp Sons ISBN 0 471 38437 2 Dalrymple G B Grove M Lovera O M Harrison T M Hulen J B Lanphere M A 1999 Age and thermal history of the Geysers plutonic complex felsite unit Geysers geothermal field California a 40Ar 39Ar and U Pb study Earth and Planetary Science Letters 173 3 285 298 Bibcode 1999E amp PSL 173 285D doi 10 1016 S0012 821X 99 00223 X Ludwig K R Renne P R 2000 Geochronology on the Paleoanthropological Time Scale Evolutionary Anthropology 9 2 101 110 doi 10 1002 sici 1520 6505 2000 9 2 lt 101 aid evan4 gt 3 0 co 2 w S2CID 83948790 Archived from the original on 2013 01 05 Renne P R Sharp W D Deino A L Orsi G and Civetta L 1997 Science 277 1279 1280 40Ar 39Ar dating into the historical realm Calibration against Pliny the Younger PDF Archived from the original PDF on 2008 10 30 Retrieved 2008 10 25 Plastino W Kaihola L Bartolomei P Bella F 2001 Cosmic Background Reduction In The Radiocarbon Measurement By Scintillation Spectrometry At The Underground Laboratory Of Gran Sasso Radiocarbon 43 2A 157 161 doi 10 1017 S0033822200037954 Hajdas Irka Ascough Philippa Garnett Mark H Fallon Stewart J Pearson Charlotte L Quarta Gianluca Spalding Kirsty L Yamaguchi Haruka Yoneda Minoru 2021 09 09 Radiocarbon dating Nature Reviews Methods Primers 1 1 1 26 doi 10 1038 s43586 021 00058 7 ISSN 2662 8449 Schaefer Joerg M Codilean Alexandru T Willenbring Jane K Lu Zheng Tian Keisling Benjamin Fulop Reka H Val Pedro 2022 03 10 Cosmogenic nuclide techniques Nature Reviews Methods Primers 2 1 1 22 doi 10 1038 s43586 022 00096 9 ISSN 2662 8449 S2CID 247396585 Murray Andrew Arnold Lee J Buylaert Jan Pieter Guerin Guillaume Qin Jintang Singhvi Ashok K Smedley Rachel Thomsen Kristina J 2021 10 28 Optically stimulated luminescence dating using quartz Nature Reviews Methods Primers 1 1 1 31 doi 10 1038 s43586 021 00068 5 ISSN 2662 8449 S2CID 240186965 Hnatyshin D and Kravchinsky V A 2014 Paleomagnetic dating Methods MATLAB software example Tectonophysics doi 10 1016 j tecto 2014 05 013 1 Brasier M D Sukhov S S 1 April 1998 The falling amplitude of carbon isotopic oscillations through the Lower to Middle Cambrian northern Siberia data Canadian Journal of Earth Sciences 35 4 353 373 Bibcode 1998CaJES 35 353B doi 10 1139 e97 122 Demidov I N 2006 Identification of marker horizon in bottom sediments of the Onega Periglacial Lake Doklady Earth Sciences 407 1 213 216 Bibcode 2006DokES 407 213D doi 10 1134 S1028334X06020127 S2CID 140634223 David Weishampel The Evolution and Extinction of the Dinosaurs 1996 Cambridge Press ISBN 0 521 44496 9 Julia Jackson Glossary of Geology 1987 American Geological Institute ISBN 0 922152 34 9 Smith J B Lamanna M C Lacovara K J Dodson Poole Jnr P Giegengack R 2001 A Giant Sauropod Dinosaur from an Upper Cretaceous Mangrove Deposit in Egypt PDF Science 292 5522 1704 1707 Bibcode 2001Sci 292 1704S doi 10 1126 science 1060561 PMID 11387472 S2CID 33454060 Further reading EditSmart P L and Frances P D 1991 Quaternary dating methods a user s guide Quaternary Research Association Technical Guide No 4 ISBN 0 907780 08 3 Lowe J J and Walker M J C 1997 Reconstructing Quaternary Environments 2nd edition Longman publishing ISBN 0 582 10166 2 Mattinson J M 2013 Revolution and evolution 100 years of U Pb geochronology Elements 9 53 57 Geochronology bibliography Talk Origins ArchiveExternal links EditInternational Commission on Stratigraphy BGS Open Data Geochronological Ontologies Retrieved from https en wikipedia org w index php title Geochronology amp oldid 1171386692, wikipedia, wiki, book, books, library,

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