1. 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?

2. Penny Lab

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

4. 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.

5. 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

6. 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.

7. 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.

8. 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

9. 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?)

10. 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?