The discovery of radioactivity and its application to dating rocks is perhaps one of the greatest scientific achievements affecting the Earth Sciences.With the discovery of radioactive isotopes more then one hundred years ago, scientists quickly realized that the radioactive decay of materials found in rocks could be used to date the rocks and consequently change the "relative" geologic time scale into an "absolute" time scale.Because of their unique decay rates, different elements are used for dating different age ranges.
In this activity, you will be able to combine your knowledge of relative dating methods (learned in Activity 7) with the absolute dating method to determine more accurately the geologic history of a region.
Activity 8 is taken from Investigating Earth: A Geology Laboratory Text (1997) by Wiswall and Fletcher.
Sedimentary rock is made of particles derived from other rocks, so measuring isotopes would date the original rock material, not the sediments they have ended up in.
However, there are radiometric dating methods that can be used on sedimentary rock, including luminescence dating.
Others measure the subatomic particles that are emitted as an isotope decays.