Perhaps the most widely used evidence for the Theory of Evolution through Natural Selection is the fossil record.
The fossil record may be incomplete and may never fully completed, but there are still many clues to evolution and how it happens within the fossil record.
Absolute monarchy is recorded from 1735 (absolute king is recorded from 1610s); scientific absolute magnitude (1902), absolute value (1907) are 20c.
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.
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.
Scientists can use certain types of fossils referred to as index fossils to assist in relative dating via correlation.
Index fossils are fossils that are known to only occur within a very specific age range.
The half-lives of several radioactive isotopes are known and are used often to figure out the age of newly found fossils.
Different isotopes have different half-lives and sometimes more than one present isotope can be used to get an even more specific age of a fossil.
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.