How Would We Use Isotopic Ages to Infer the Ages

Multiple Choice

How would we use isotopic ages to infer the ages of the upper and lower unit in this diagram?

A) The lower unit would be younger than an age on the crosscutting dike.
B) The upper unit would be older than an age determined on pebbles of the dike in that unit.
C) The dike is younger than the lower unit but older than the upper unit.
D) An age on the dike would not help us because it is an igneous rock.