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

Penny Lab

Absolute Dating AKA Radiometric dating Determines ‘exact’ age. Examples: Dinosaurs went extinct 65 million years ago. Trey was born on June 29, 2000.

Radioactive Decay Radioactive Elements Unstable parent nuclei becoming stable daughter nuclei Gives off energy Constant rate By measuring how much of each type of radioactive element is present scientists can determine a rocks age.

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

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.

Carbon Dating Think through the math: If there is 50% of the original amount of 14C in a specimen it is 5730 years old. If you find a specimen that has only 25% of the original 14C, it has gone through 2 half- lives. This specimen is (5730x2) years old = 11,460 years old. I am going to do these examples with my students.

Carbon Dating: Fill in this Chart! Half-Life % Carbon Left Age in Years 1 50% 5,730 2 25% 11,460 3 12.5% 17,190 4 6.25% 22,920 5 3.125% 28,650 6 1.563% 34,380 7 0.781% 40,110

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

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