One of the most popular of these is known as radiometric dating. can be In other words, something in the past caused a significant amount of helium to build up inside these zircons (such as from a rapid decay episode of uranium), yet, in spite of the fact that helium has been observed to leak out readily from these zircons, it has not done so: simply because it hasn't had enough time to do so -- suggesting that the zircons themselves are only a few thousand years old."There is evidence to show ...

However, not as well known is the fact that such methods have serious flaws which are often glossed over, or ignored when writing on, or discussing this subject in public. that (the) half-lives (of uranium-thorium-lead) are not constant but vary with time. comes from the study of pleochroic haloes which form in a rock in the following way.

In other words, the magnitude of the radius of a pleochroic halo in a particular crystal depends on the half-life of the decay responsible for the alpha particle emission. the radii of pleochroic haloes corresponding to a definite decay in a particular mineral are ...(the same) size, then it can be safely assumed that the half-life of that decay is a constant. Because of this decay, the helium content of any mineral or rock capable of retaining helium will increase during the lifetime of that mineral or rock, and the ratio of helium to its radioactive progenitors then becomes a measure of , helium dating provided most of the dates used in the early geologic time scales.This same inaccuracy is inherant in all other methods of radiological dating.Nothing says that the levels of carbon 14 are or were constant at any point in history, or that the levels of solar radiation that cause the isotope in the atmosphere were ever constant." Carbon dating has been calibrated against other methods (dendrochronology, artifacts of known provenance, annually layered sediments and so on).