Editing Radiometric dating (section)

===Accuracy of radiometric dating===
[[File:Thermal ionization mass spectrometer.jpg|thumb|[[Thermal ionization mass spectrometer]] used in radiometric dating.]]
The basic equation of radiometric dating requires that neither the parent nuclide nor the daughter product can enter or leave the material after its formation. The possible confounding effects of contamination of parent and daughter isotopes have to be considered, as do the effects of any loss or gain of such isotopes since the sample was created. It is therefore essential to have as much information as possible about the material being dated and to check for possible signs of [[Metasomatism|alteration]].<ref>{{cite journal|doi=10.1016/0012-821X(96)00132-X |title=3-D, <sup>40</sup>Ar-<sup>39</sup>Ar geochronology in the Paraná continental flood basalt province |year=1996 |journal=Earth and Planetary Science Letters |volume=143|issue=1–4 |pages=95–109 |bibcode=1996E&PSL.143...95S|last1=Stewart |first1=Kathy |last2=Turner |first2=Simon |last3=Kelley |first3=Simon |last4=Hawkesworth |first4=Chris |last5=Kirstein |first5=Linda |last6=Mantovani |first6=Marta }}</ref> Precision is enhanced if measurements are taken on multiple samples from different locations of the rock body. Alternatively, if several different minerals can be dated from the same sample and are assumed to be formed by the same event and were in equilibrium with the reservoir when they formed, they should form an [[isochron dating|isochron]]. This can reduce the problem of [[contamination]]. In [[uranium–lead dating]], the [[concordia diagram]] is used which also decreases the problem of nuclide loss. Finally, correlation between different isotopic dating methods may be required to confirm the age of a sample. For example, the age of the [[Geology of Greenland|Amitsoq gneisses from western Greenland]] was determined to be 3.60 ± 0.05 [[Gigaannum|Ga]] (billion years ago) using uranium–lead dating and 3.56 ± 0.10 Ga (billion years ago) using lead–lead dating, results that are consistent with each other.<ref>{{cite book|last1=Dalrymple|first1=G. Brent|title=The age of the earth|date=1994|publisher=Stanford Univ. Press|location=Stanford, Calif.|isbn=9780804723312}}</ref>{{rp|142–143}}

Accurate radiometric dating generally requires that the parent has a long enough half-life that it will be present in significant amounts at the time of measurement (except as described below under "Dating with short-lived extinct radionuclides"), the half-life of the parent is accurately known, and enough of the daughter product is produced to be accurately measured and distinguished from the initial amount of the daughter present in the material. The procedures used to isolate and analyze the parent and daughter nuclides must be precise and accurate. This normally involves [[isotope-ratio mass spectrometry]].<ref>{{cite book|last1=Dickin|first1=Alan P.|title=Radiogenic isotope geology|date=2008|publisher=Cambridge Univ. Press|location=Cambridge|isbn=9780521530170|pages=15–49|edition=2nd}}</ref>

The precision of a dating method depends in part on the half-life of the radioactive isotope involved. For instance, carbon-14 has a half-life of 5,730 years. After an organism has been dead for 60,000 years, so little carbon-14 is left that accurate dating cannot be established. On the other hand, the concentration of carbon-14 falls off so steeply that the age of relatively young remains can be determined precisely to within a few decades.<ref>{{cite journal|year=2004
|title=INTCAL04 Terrestrial Radiocarbon Age Calibration, 0–26 Cal Kyr BP
|journal=Radiocarbon
|volume=46
|issue=3
|pages=1029–1058
|doi=10.1017/S0033822200032999
|doi-access=free
|bibcode=2004Radcb..46.1029.
|hdl=10289/3690
|hdl-access=free
}}</ref>