It is based on the fact that some of the radioactive isotope of Potassium, Potassium-40 (K-40) ,decays to the gas Argon as Argon-40 (Ar-40).
By comparing the proportion of K-40 to Ar-40 in a sample of volcanic rock, and knowing the decay rate of K-40, the date that the rock formed can be determined.
It is clear that the sedimentary rock was deposited and folded before the dyke was squeezed into place.
By looking at other outcrops in the area, our geologist is able to draw a geological map which records how the rocks are related to each other in the field.
Potassium-Argon Dating Potassium-Argon dating is the only viable technique for dating very old archaeological materials.
Geologists have used this method to date rocks as much as 4 billion years old.
Love-hungry teenagers and archaeologists agree: dating is hard.