1. Absolute Dating: A Measure of Time January 27,2015

2. Focus Activity Good Morning! Come in and sit down quietly. On your “Table of Contents” add “KWL Absolute Dating” Sit quietly for instructions!

3. K-W-L Chart  K- What you do you already know about ABSOLUTE DATING? W- What do you want to know about ABSOLUTE DATING? Leave the “L” section empty!

4. Homework!  Complete Earth History WebQuest 2 and Relative Dating worksheet!  Turn homework in by Wednesday!  Get your report card and merit event form signed!  Bring in “ Student Teaching” Form

5. Review : Geology and Relative Dating  Uniformitarianism  Catastrophism  Paleontology  Relative Dating  Superposition  Geologic Column  Unconformities

6. Absolute Dating  The process of getting the age of an object by determining the number of years it has existed.

7. Radioactive Decay!  Radioactive decay occurs at a steady rate, scientist can use the relative amounts of stable and unstable isotopes present in an object to determine age!  To date rock, scientist compare parent material to daughter material.

8. RADIOACTIVE DATING  Radiometric Dating – the most common method of absolute dating. Determining the absolute age of rock based on the ratio of parent material to daughter material present!

9. ISOTOPES  Radioactive decay occurs when radioactive isotopes (parent) break into stable (daughter) isotopes.

10. ISOTOPES: Part 2  Scientist analyze isotopes of radioactive elements.  Atoms of the same element have the same number of protons but have different numbers of neutrons. ISOTOPES! 2 minutes to copy  Copy Figure 1: Radioactive Decay

11.  Unstable radioisotope is called the parent isotope. Unstable isotopes are radioactive!

12.  Stable isotopes stay in their original form. Stable radio isotopes are called Daughter!  Parent: The unstable radioactive isotopes!

13. Radiometric Dating Determining the absolute age of a sample,based on the ratio of parent material and daughter material!

14. HALF-LIFE To date rock, scientist compare parent material to daughter material. U-238Half-life = 4.5 Billion Years K-40Half-life = 1.25 Billion Years C-14Half-life = 5, 730 Years

15. HALF LIFE  The half-life of an element is the time it takes for half of the material you started with to decay.  2. Each element has it’s own half-life

16. Understanding Half-Life  Each element decays into a new element  C14 decays into N14  4. The half-life of each element is constant. It’s like a clock keeping perfect time.  Now let’s see how we can use half-life to determine the age of a rock, fossil or other artifact.

17. Half Life! JUST CUT IT IN HALF!

18. Example  The half-life of Zn-71 is 2.4 minutes. If one had 100.0 g at the beginning, how many grams would be left after 7.2 minutes has elapsed?  7.2 / 2.4 = 3 half-lives  (1/2)3 = 0.125 (the amount remaining after 3 half-lives)  100.0 g x 0.125 = 12.5 g remaining

19. Half Life Equations  You have 150 grams of Iron-59, a radioactive isotope. Its half- life is 50 days. How many grams of Iron-59 will you have left at the end of 100 days?

20. Practice Problems:  4.A radioactive element has a half-life of 42 days. How much of a 100gram sample will be left after:  A)42 days  B)84 days  C)168 days

21. Radiometric Dating Potassium-Argon Method Uranium-Lead Method Rubidium-Strontium Method Carbon 14 Method

22. Potassium –Argon Potassium 40 is isotope used for radiometric dating. Potassium 40 has a half life of 1.3 billion years. It decays to argon and calcium. Measures amount of argon present. Used to date material older than 100,000 years.

23. Uranium-Lead Method  Uranium 238 radioactive isotope decays to lead 206. Half life is 4.5 billion years. Older rock has more lead 206 daughter material present. Dates rock more than 10 million years!

24. Rubidium –Strontium  Unstable radioactive parent isotope rubidium 87 forms strontium 87 stable daughter isotope. Half life is 49 billion years. Date rock older than 10 million years.

25. Carbon-14  Carbon 14 decreases when plants or animals decay. Half life is 5730 years. Date materials that have lived within the past 50,000 years.

26. CARBON 14 METHOD

27. http://evolution.berkeley.edu/evosite/li nes/images/strat_column.gif

28. COMPLETE THE “L” SECTION