And yet the different methods of radiometric dating produce dates that are consistent with each other. Since each different radiometric method uses materials that have different chemical and physical properties, we would expect that issues of contamination, leakage, wrong initial amounts, and so forth would cause the different methods to produce different age estimates when applied to the same geologic units. Yet, these different methods will produce the same ages for the same geologic units.
So it seems that the potential problems of extra decay products or contamination or leakage of parent isotope aren't serious issues after all.
Speaking personally, I find few things more awesome than contemplating this vast and majestic process of evolution, the ebb and flow of successive biotas through geological time. Creationists and others who cannot for ideological or religious reasons accept the fact of evolution miss out a great deal, and are left with a claustrophobic little universe in which nothing happens and nothing changes. -- M. Alan Kazlev
It takes a very long time for uranium to decay into lead. Who even lived that long to observe this? If this is not how they determine the half life, then in what method do they use to determine the half life? I think it has to do with calculations.
As was pointed out, the formula describing decay is very well understood. As time passes, the amount of material that is left given by the formula
where A0 is the amount of the radioactive material that you start with.
A little bit of calculus, and we find that the number of decays you measure in a given amount of time, say in a second or a minute, is given by
decays per unit of time = A0 ln 2 /h 2-t/h
If the half life, h, is very long, then 2-t/h stays close to 1 during the length of time of the experiment, and so
decays per unit of time = A0 ln 2 /h
So one can measure the half life of a material just by measuring the amount of the material tha tone has, and measuring the number of decays that occur during a short amount of time.
Of course, there are practical issues in making these measurements, but as an undergraduate, I measured half lives of various radioactive materials, some of which have half-lives of millions of years.
Edited by Chiroptera, : Removed some minus signs.
Edited by Chiroptera, : Forgot the base of the exponent, heh.
Edited by Chiroptera, : Oops. Meant to write 2 instead of e.
Edited by Chiroptera, : *sigh* Will I ever get this right? Serves me right for trying to mix College Algebra with Calculus.