1. Radioactive Dating
Section 10.3

2. Radioactive 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

3. Radioactive Decay
The 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.
Energy
Unstable atom
Stable atom
Particles

4. Radioactive Decay % Radioactive Material Remaining
Number of Half-Lives

5. Radioactive Decay Different elements have different half-lives
Radioactive Element Half-life (years)
Carbon-14 5,730
Potassium billion
Rubidium billion
Thorium billion
Uranium million
Uranium billion

6. Radioactive 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.

7. Radioactive 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?

8. Radioactive 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?