== Basic mechanism ==
Radiometric dating proceeds from the fact that certain substances (radioactive isotopes) decay, with near-clockwork accuracy, into other elements, and that the old elements and the new elements can be chemically distinguished and can be quantitatively measured. Even the individual isotopes of an element can be accurately measured, though they can't be chemically separated. The radioactive decay of a given isotope proceeds by a well-known [[Radioactivity#Exponential_decay_and_halfExponential decay and half-life|exponential decay function]] involving a "half-life" for that isotope:
::<math>e^{-\frac{log(2)}{H}\ t}</math>
where H is the half-life.
Needless to say, radiometric dating is not easy. It requires very careful measurement and analysis technique, as well as careful analysis of the assumptions, about such things as the purity and composition of the samples, to do this effectively. There are also assumptions about the accuracy of the equipment involved, and, of course, assumptions about the fundamental physics involved. The findings of the scientific community, on such things as the age of the Earth and the dates of various epochs (e.g. Permian, Triassic, Cretaceous, Paleogene) are the result of decades of measurement and analysis by hundreds of people.
All scientific investigations involve three general types of asumptionsassumptions:
#The scientists doing the investigation know how to perform the investigation—in short, they know what they are doing. If one is investigating temperature patterns to draw conclusions and predictions about weather, this means that the investigators understand the subject matter, and understand the connection between temperature and weather patterns.
#The equipment works, is properly maintained, and is properly calibrated. That is, the thermometers work properly.
There is a fairly well-known example of chemical state affecting electron capture activity. The <sup>7</sup>Be nucleus (Beryllium-7) is an electron capturer with a half-life of about 53 days, turning into Lithium-7. The variation is about 1.5%. While this half-life is way too short to be useful for radiometric dating, the effect of the chemical state is noticeable. The reason is that, because the atomic number is only four, the 2s valence electrons are very close to the 1s electrons involved in capture.<ref>Huh, C.-A., Dependence of the decay rate of <sup>7</sup>Be on chemical forms, Earth and Planetary Science Letters 171:325–328, 1999.</ref> See [[Systematics of beta decay]] for more details.
There is no good reason to expect that the rate of decay of a radioactive material is largely constant. Nevertheless, and it was almost certainly not constant near some creationists, perhaps with a goal of calling into question the creation or beginning reliability of radiometric dating for the universepurpose of advancing a "young Earth" doctrine, raise objections about the science.<ref>Sibley, Andrew (August 2013). [https://creation.com/radioactive-decay-rates-and-solar-activity Variable radioactive decay rates and the changes in solar activity] (a creationist website). ''Creation Ministries International'' (from the ''Journal of Creation 27(2):3–4''). Retrieved January 4, 2018.</ref><ref>Wieland, Carl. [https://creation.com/rate-group-reveals-exciting-breakthroughs RATE group reveals exciting breakthroughs!] (a creationist website). ''''Creation Ministries International''. Retrieved January 4, 2018.</ref><ref>Walker, Tas (April 2000). [https://creation.com/radioactive-decay-rate-depends-on-chemical-environment Radioactive decay rate depends on chemical environment] (a creationist website). ''Creation Ministries International'' (from the ''Journal of Creation 14(1):4–5''). Retrieved January 4, 2018.</ref><ref>Woodmorappe, John (August 2001). [https://creation.com/billion-fold-acceleration-of-radioactivity-demonstrated-in-laboratory Billion-fold acceleration of radioactivity demonstrated in laboratory] (a creationist website). ''Creation Ministries International'' (from the ''Journal of Creation 15(2):4–6''). Retrieved January 4, 2018.</ref><ref>Thomas, Brian (August 5, 2009). [https://www.icr.org/article/4816 Radioactive Decay Rates Not Stable] (a creationist website). ''Institute for Creation Research''. Retrieved January 4, 2018.</ref><ref>Snelling, Andrew A. (October 1, 2009). [https://answersingenesis.org/geology/radiometric-dating/radiometric-dating-problems-with-the-assumptions/ Radiometric Dating: Problems with the Assumptions] (a creationist website). ''Answers in Genesis''. Retrieved January 4, 2018.</ref><ref>Knapp, Alex (May 3, 2011). [https://www.forbes.com/sites/alexknapp/2011/05/03/radioactive-decay-rates-may-not-be-constant-after-all/#4634f095147f Radioactive Decay Rates May Not Be Constant After All]. ''Forbes''. Retrieved January 4, 2018.</ref> One common objection relates to Beryllium-7, explained above. The discrepancy is very small. Another involves a very large discrepancy, that can be provoked in a particle accelerator, by radically altering the electron cloud. The conditions for this to happen do not occur in nature. There are other tiny discrepancies, apparently related to the rotation of the Sun. One general claim that creationists make is that "Radioactive decay rates were almost certainly not constant near the creation or beginning of the universe" without giving any reason for this belief. But even if decay rates changed wildly in the earliest days of the universe, if they have stayed essentially constant for 13 billion years, the universe must be at least 13 billion years old.
For a fairly technical explanation of the radioactivity process, see the [[Radioactivity|radioactivity page]].