Here is an easy-to understand analogy for your students: relative age dating is like saying that your grandfather is older than you.
Absolute age dating is like saying you are 15 years old and your grandfather is 77 years old.
To determine the relative age of different rocks, geologists start with the assumption that unless something has happened, in a sequence of sedimentary rock layers, the newer rock layers will be on top of older ones. This rule is common sense, but it serves as a powerful reference point.
Index fossils are fossils that are known to only occur within a very specific age range.The requirement of identical burial conditions means that fluoride dating works best when it is applied within a single site with little variation in soil chemistry.Many different techniques can be used to measure bone fluoride content, but measurement by ion selective electrode is the easiest and simplest method available today.Bones are primarily composed of the mineral calcium hydroxy apatite.When exposed to water that contains fluoride, a fluoride ion (F-) can replace a hydroxyl ion (OH-) in the bone mineral.