The Christian Creationists have criticised it on the grounds that it is innacurate.But these innacuracies are the result of variation in the level of Carbon 14 in the atmosphere, and when this is worked out (through calibration with tree rings of the bristlecone pine, the oldest living organism) precise dates can be had.(The item being tested must be organic based, and must be dead - tests on live mollusks showed an age of 2000 years).

Even in the case of very long half-lives, modern scientific instruments are now accurate enough to give very fine readings.

We usually hear of Carbon 14 dating, which is very important in archaeology.

With the discovery of radiometric dating, it became possible for the first time to attempt precise figures.

Radiometric dating works on the principle that certain atoms and isotopes are unstable.

The Greeks had the "great year" of 24,500 years, based on the precession of the equinoxes.

The time-scale of the fundamentalist or Creationist Judeo-Christian is based on a word-for-word reading of the first book of the Bible, and assumes a total age of the earth and the cosmos of a mere 5 or 6,000 (some Creationists allow 10,000) years.

Fortunately, we are able to date older fossils using the radiometric breakdown of other elements (Potassium-Argon dating, Argon-Argon dating, and Rubidium dating [I'm writing this without any refs - so this last one might be wrong]).

Usually the radioactive 'clocks' for these elements are started when the elements are deposited by a volcanic eruption (usually in the form of ash).

However, although 5730 years is the correct half-life, it is not the one used for most C-14 dating, simply because the original half-life used to determine dates back in the 1950s was wrong, and to be consistent we still tend to use the wrong value (a bit like the direction of current flow in electronics, which is the opposite of that which the electrons take, but was the original and incorrect assumption).