Potassium-40 (40K) is a radioactive material that decays into argon-40 (40Ar). The half-life of a sample of 40K is 1.3 billion years. Rocks containing 40K have been around since the formation of the earth, and 40Ar gas has been accumulating in those rocks since the earth formed. However, when rocks are heated by volcanic action, all the 40Ar leaves the rock when the gases escape. Create a scenario and discuss, based on your knowledge of half-life, the value of potassium-argon dating to geologists.