Radiometric method for dating rocks
Sedimentary rock forms in layers over millions of years.
If you look at a cliff made from sedimentary rock, you’ll notice distinct layers that may even be different colors.
Enjoyed the Easy Geography for Kids all about Layers of Rocks info?
Activity: Further discussion: Good overview as relates to the Grand Canyon: age dating: Use with this cross section of the Grand Canyon from the USGS’s teaching page: Canyon Have students reconstruct a simple geologic history — which are the oldest rocks shown? Are there any that you can’t tell using the Rule of Superposition?
I also like this simple exercise, a spin-off from an activity described on the USGS site above.
If a rock has been partially melted, or otherwise metamorphosed, that causes complications for radiometric (absolute) age dating as well.
Like the other kind of dating, geologic dating isn’t always simple.