What is Geochronology?
'''Geochronology''' is the science of finding the ages of [[rocks]], [[fossils]] and [[sediments]]. It uses a number of methods.<ref>Renne P.R; Ludwig K.R.& Karner D.B. 1998. Progress and challenges in geochronology. ''Science Progress'', '''83''', 107–121 [https://www.ncbi.nlm.nih.gov/pubmed/10800377]</ref><ref>Noller J.S; Sowers J.M.& Lettis W.R., 2000. ''Quaternary geochronology: methods and applications''. ''American Geophysical Union'', AGU Reference Shelf 4.</ref><ref>Colman S.M; Pierce K.L.& Birkeland P.W. 1987. Suggested terminology for Quaternary dating methods. ''Quaternary Research'', '''28''', 314–319.</ref> Geochronology is the main tool used to get absolute age dates for all fossil assemblages, and for the history of the Earth and other bodies. == Dating methods == === Radiometric dating === {{main|Radiometric dating}} By measuring the amount of [[radioactive decay]] of a [[radioactive]] [[isotope]] with a known [[half-life (element)|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 dating|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.<ref>Dickin A.P. 1995. ''Radiogenic isotope geology''. Cambridge University Press. {{ISBN|0-521-59891-5}}</ref><ref>Faure G. 1986. ''Principles of isotope geology''. Cambridge University Press. {{ISBN|0-471-86412-9}}</ref><ref>Faure G. & Mensing D. 2005. ''Isotopes - principles and applications''. 3rd ed, Wiley. {{ISBN|0-471-38437-2}}</ref> Two or more radiometric methods can be used in concert to achieve more robust results.<ref>Dalrymple G.B. ''et al'' 1999. Age and thermal history of the Geysers plut