Absolute radiometric dating
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.
Geologists draw on it and other basic principles ( to determine the relative ages of rocks or features such as faults.
Relative age dating also means paying attention to crosscutting relationships.
Absolute age dating is like saying you are 15 years old and your grandfather is 77 years old.