Radiometric dating applied to sedimentary rocks
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.
This uses radioactive minerals that occur in rocks and fossils almost like a geological clock.
It’s often much easier to date volcanic rocks than the fossils themselves or the sedimentary rocks they are found in.
Using relative dating the fossil is compared to something for which an age is already known.
For example if you have a fossil trilobite and it was found in the Wheeler Formation.
The science of geochronology is the prime tool used in the discipline of chronostratigraphy, which attempts to derive absolute age dates for all fossil assemblages and determine the geologic history of the Earth and extraterrestrial bodies.
Geochronology is different in application from biostratigraphy, which is the science of assigning sedimentary rocks to a known geological period via describing, cataloguing and comparing fossil floral and faunal assemblages.
Scientists can use certain types of fossils referred to as index fossils to assist in relative dating via correlation.