1. Warm-up 1. How do scientists use ‘relative dating?’ 2. Which layer is the oldest? 3. Which layer is the youngest? 4. Which layers are older than the fault line B?

2. Absolute Dating Determines ‘exact’ age. Examples: ◦ The event happened 65 million years ago. ◦ Renzo was born on August 1, 2000.

3. Radioactive Decay Radioactive Elements Unstable parent nucleus emits energy at a constant rate becoming stable daughter nucleus By measuring how much of each type of radioactive element is present scientists can determine a rocks age.

4. Half-Life Amount of time it takes for half of the amount of a radioactive element to decay into another element. Uranium-235 Potassium-40 Carbon-14

5. Carbon Dating Many forms of carbon Carbon-14 ◦ Radioactive ◦ Living - continuous replacement ◦ Dead – amount decreases ◦ Half-life = 5,730 years By measuring the amount of Carbon-14 remaining in the specimen scientists can determine its age.

6. Carbon Dating Carbon Dating Think through the math: If there is 50% of the original amount of 14 C in a specimen it is 5730 years old. If you find a specimen that has only 25% of the original 14 C, it has gone through 2 half- lives. ◦ This specimen is (5730x2) years old = 11,460 years old.

7. Carbon Dating: Fill in this Chart! Half-Life% Carbon LeftAge in Years 150%5,730 225%11,460 312.5%17,190 46.25%22,920 53.125%28,650 61.563%34,380 70.781%40,110

8. You are a CSI Detective… You found a skeleton that contains 12.5% of it’s original carbon. 1.How many half lives have passed? 2.How old is it? (how long ago did this person die?)

9. You are an anthropologist and found this animal! This skeleton contains 3.125% of it’s original carbon. 1.How many half lives have passed? 2.How old is it?