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Radiometric dating involves dating rocks or other objects by measuring the extent to which different radioactive isotopes or nuclei have decayed.

## Contents

Although the time at which any individual atom will decay cannot be forecast, the time in which any given percentage of a sample will decay can be calculated to varying degrees of accuracy. The time it takes for half of a sample to decay is known as the half life of the isotope. 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 are useful for dating once-living objects (since they include atmospheric carbon from when they lived) from about ten to fifty thousand years old. See Carbon dating. Longer-lived isotopes provide dating information for much longer ago. The key is to measure one that has had time to decay a measurable amount, but not so much as to only leave a trace remaining. Given isotopes are useful for dating over a range from a fraction of their half life to about four or five times their half life.

## How it works

The statistics of decay for every radioactive nuclide follow the same decay law:

$N = N_0 e^{-k t} \!$

where

$k = \frac{\ln 2}{\tau_{1/2}}$

is the decay constant, $\tau_{1/2}$ is the half-life of the element, $t$ is the time expired since the sample contained $N_0$ atoms of the nuclide, and $N$ is the remaining amount of nuclide. We can measure $N$ directly and obtain a good estimate of $N_0$ by analyzing the chemical composition of the sample. The half-life $\tau_{1/2}$, 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.[1] Solving this equation for $t$ gives us the estimated age of the sample:

$t = \frac{\tau_{1/2}}{\ln 2} \ln \frac{N_0}{N}$

Radiometric dating frequently reveals that rocks, fossils, etc. are very much older than the approximately 6,000 to 10,000 years reckoned by young earth creationists. YEC biblical literalists are necessarily bound to the dogmatic religions conclusion that the Earth is of a certain age based on a particular literal interpretation of the Genesis creation myth. They tie themselves in logical knots trying to reconcile the results of radiometric dating with the unwavering belief that the Earth was created ex nihilo about 6,000 to 10,000 years ago. Indeed, special creationists have for many years held that where science and their religion conflict, it is a matter of science having to catch up with scripture, not the other way around.[2] [3] [4]

One way Young Earth Creationists and other denialists try to discredit radiometric dating is to cite examples radiometric dating techniques providing inaccurate results. This is frequently because the selected technique is used outside of its appropriate range, for example on very recent lavas. The Institute for Creation Research's RATE project aimed to show scientifically that methods of radiometric dating produced wildly inconsistent and incorrect values. Ultimately these "creation scientists" were forced to admit that even for methods they accepted as sound, the age of the Earth would be vastly greater than the 6,000 they set out to prove.