Chemistry / Chem 2530 · Procedure · 60–90 seconds
Radiometric Dating from a Decay Ratio
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Radiometric dating means comparing a sample's present ratio of a radioactive isotope to its stable decay product, or to a stable reference isotope, against the ratio expected at the sample's formation, and solving the first-order decay relationship for elapsed time using the isotope's known half-life.
If a sample's carbon-14 activity has fallen to 79% of the activity expected in freshly formed organic matter, solving the first-order relationship with carbon-14's 5730-year half-life gives an elapsed time of roughly 1950 years since the organism died.
This method assumes the starting ratio at formation is known or can be reasonably estimated — applying it to a sample whose initial isotope ratio is not actually comparable to the assumed baseline produces a confidently wrong date.
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