How is radiometric dating done
The rate of decay (given the symbol λ) is the fraction of the 'parent' atoms that decay in unit time.For geological purposes, this is taken as one year. There are two main methods determining a fossils age, relative dating and absolute dating.Relative dating is used to determine a fossils approximate age by comparing it to similar rocks and fossils of known ages.Typically commonly occurring fossils that had a widespread geographic distribution such as brachiopods, trilobites, and ammonites work best as index fossils.If the fossil you are trying to date occurs alongside one of these index fossils, then the fossil you are dating must fall into the age range of the index fossil. In a hypothetical example, a rock formation contains fossils of a type of brachiopod known to occur between 410 and 420 million years.Using relative dating the fossil is compared to something for which an age is already known.
The atoms in some chemical elements have different forms, called isotopes.
These isotopes break down at a constant rate over time through radioactive decay.
By measuring the ratio of the amount of the original (parent) isotope to the amount of the (daughter) isotopes that it breaks down into an age can be determined.
Absolute dating is used to determine a precise age of a fossil by using radiometric dating to measure the decay of isotopes, either within the fossil or more often the rocks associated with it.
The majority of the time fossils are dated using relative dating techniques.