Radiometric dating controversy
It suffers from the problem that rubidium and strontium are very mobile and may easily enter rocks at a much later date to that of formation.This method for rock dating is based on the decay of potassium-40 into argon: until the rock solidifies, argon can escape, so it can in theory date the formation of rock.This is consistent with the assumption that each decay event is independent and its chance does not vary over time.The solution is: where is the half-life of the element, is the time expired since the sample contained the initial number atoms of the nuclide, and is the remaining amount of the nuclide.One problem is that potassium is also highly mobile and may move into older rocks.This depends on the decay of uranium-237 and uranium-238 to isotopes of lead.
A proper radiometric date should read years before present (with 1950 being present) ± range/2 at x standard deviations (Xσ)', but is often reported as a single year or a year range, like 1260–1390 CE (the date for the Shroud of Turin).
Some isotopes have half lives longer than the present age of the universe, but they are still subject to the same laws of quantum physics and will eventually decay, even if doing so at a time when all remaining atoms in the universe are separated by astronomical distances.
Various elements are used for dating different time periods; ones with relatively short half-lives like carbon-14 (or C) are useful for dating once-living objects (since they include atmospheric carbon from when they were alive) from about ten to fifty thousand years old. Longer-lived isotopes provide dating information for much older times.
We can measure directly, for example by using a radiation detector, and obtain a good estimate of by analyzing the chemical composition of the sample.
The half-life , specific to each nuclide, can be accurately measured on a pure sample, and is known to be independent of the chemical composition of the sample, temperature and pressure.