This radioactivity can be used for dating, since a radioactive 'parent' element decays into a stable 'daughter' element at a constant rate.The rate of decay (given the symbol λ) is the fraction of the 'parent' atoms that decay in unit time.This method is useful for igneous and metamorphic rocks, which cannot be dated by the stratigraphic correlation method used for sedimentary rocks. Some do not change with time and form stable isotopes (i.e.those that form during chemical reactions without breaking down).After all, textbooks, media, and museums glibly present ages of millions of years as fact.Yet few people know how radiometric dating works or bother to ask what assumptions drive the conclusions.
The results showed that Ötzi died over 5000 years ago, sometime between 33 BC. Uranium has a very long half-life and so by measuring how much uranium is left in a rock its approximate age can be worked out.
When they die no new carbon-14 is taken in by the dead organism.
The carbon-14 it contained at the time of death decays over a long period of time.
By dating these surrounding layers, they can figure out the youngest and oldest that the fossil might be; this is known as "bracketing" the age of the sedimentary layer in which the fossils occur.
Teach your students about absolute dating: Determining age of rocks and fossils, a classroom activity for grades 9-12.