A relative age dating activity answer key
Relative dating does not provide actual numerical dates for the rocks.Fossils are important for working out the relative ages of sedimentary rocks.
So carbon 14 is used to date materials that aren’t that old geologically, say in the tens of thousands of years, while potassium-argon dating can be used to determine the ages of much older materials, in the millions and billions year range.It’s based either on fossils which are recognized to represent a particular interval of time, or on radioactive decay of specific isotopes. Based on the Rule of Superposition, certain organisms clearly lived before others, during certain geologic times.After all, a dinosaur wouldn’t be caught dead next to a trilobite.Pretty obvious that the dike came after the rocks it cuts through, right?With absolute age dating, you get a real age in actual years.Like the other kind of dating, geologic dating isn’t always simple.
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?
For example, which is older, the bricks in a building or the building itself?
Are there repairs or cracks in the sidewalk that came after the sidewalk was built?
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.