2Radioactive Decay Since rocks are made of matter, they contain atoms Most elements are stable but some are unstable.Unstable (radioactive) elements will break down (decay) to form stable elements.Using this property we can determine the absolute age of a rock
3Radioactive DecayThe rate of decay of each radioactive element is constant. (half-life)A half-life is the time it takes for half the atoms to decay.EnergyUnstable atomStable atomParticles
4Radioactive Decay % Radioactive Material Remaining Number of Half-Lives
5Radioactive Decay Different elements have different half-lives Radioactive Element Half-life (years)Carbon-14 5,730Potassium billionRubidium billionThorium billionUranium millionUranium billion
6Radioactive Decay Activity Directions:Take a square and cut it in half. Put one piece aside. Note each time you cut the paper.Cut the piece you have in half and set one piece aside again.Continue this until you can not practically cut the square any more.
7Radioactive Decay Activity What is the total number of times you were able to cut the sample in half?Each cut represents the half-life of Carbon-14. What is the length of time represented by each cut?Multiply the number of cuts by the half-life period of C-14. What is the total amount of time represented by all your cuts?
8Radioactive Decay Activity 4) If an animal lived million of years ago, could C-14 be used to determine when it died? Why or why not?5) If an animal lived near the La Brea Tar Pits (found now in Los Angeles) 40,000 years ago, could C-14 be used to determine when it died?