Relative age dating also means paying attention to crosscutting relationships.
Say for example that a volcanic dike, or a fault, cuts across several sedimentary layers, or maybe through another volcanic rock type.
I also like this simple exercise, a spin-off from an activity described on the USGS site above.
Take students on a neighborhood walk and see what you can observe about age dates around you.
What’s more, if the whole rock is badly weathered, it will be hard to find an intact mineral grain containing radioactive isotopes.
You might have noticed that many of the oldest age dates come from a mineral called zircon.
Geologists draw on it and other basic principles ( to determine the relative ages of rocks or features such as faults.The narrower a range of time that an animal lived, the better it is as an index of a specific time.