1. Do Now: Think about this… If you were standing 10 feet from the wall, and I asked you to walk half the distance to the wall, how close would you be? If I asked you to repeat this process, would you ever reach the wall? Aim: How do scientists read rocks for an exact age?

2. Basic Atomic Structure  Electrons – orbit the nucleus.  Protons – are in the atom’s nucleus.  Neutrons - are in the atom’s nucleus. DO NOT COPY

3. I. Isotopes : UNSTABLE STABLE How are the three atoms of Hydrogen different? - PROTON - NEUTRON *too many neutrons the unstable form of an element; found in all objects (rocks, people, trees)

4. II. Radioactive Decay : The process where an Isotope breaks down losing energy and particles. *This makes the Isotope into a new stable atom* (Isotope) Describe what is happening in the diagram

5. III. Parts of Radioactive Decay Not affected by outside factors a) Unstable Radioactive Isotopes, are called Parents. b) Stable Decayed elements, are called Daughters. Looking at the graph, what happens to the number of parents and daughters over time? How many parents do we start with at time zero? Daughters?

6. Which color dot represents the Parent elements? Which represents the Daughters? How many parents do we loose each time?

7. cover of your ESRT - Knowing the rate of decay and the ratio of Parent Isotopes to Daughter elements, we can figure out how old the object is. c) Half – Life - time required for 50% of the unstable Parent Isotopes to decay (change) into stable daughter elements. - This time is constant and not affected by outside factors.

8. V. Common Isotopes Carbon 14 -Used to date most recent organic material. (anything once living) -Shortest half-life. How long is the half-life for Carbon 14 ? How does this compare to the other Isotopes?

9. Examples: Use your ESRT How many years will it take for two half- lives to pass of C14? What % of C14 will remain at this point? Which isotope has the longest half life? What is it? 11,400 yrs 25% C14 will remain Rubidium-87 ( 87 Rb) MAKE A CHART!

10. If you can see in a rock sample there is 25% (1/4) C 14 and 75% (3/4) N 14, the sample must have gone through how many half-lives? Two half-lives. How old is this sample? 11,400 yrs old.

11. A student found a fossil and by looking at the radioactive decay of C14 she found there to be 1/16 th of C 14 remaining in the fossil. How many half lives has this sample gone through? The sample has gone through 4 half- lives

12. What is the half life of Strontium 90? 25 years

13. 22,8001/164 17,1001/83 11,4001/42 5,7001/21 01/10 Number of years % Parent Remaining Half-Life THE CHART THAT MAKES HALF-LIFE EASIER

14. Closure: Take a worksheet from the back top bin