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?

Absolute Dating

Determines ‘exact’ age.Examples:◦The event happened 65 million years ago.

◦Renzo was born on August 1, 2000.

Radioactive DecayRadioactive 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.

Half-LifeAmount of time it

takes for half of the amount of a radioactive element to decay into another element.

Uranium-235Potassium-40Carbon-14

Carbon DatingMany 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.

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.

1. How many half lives have passed?

2. 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.1. How many half lives have passed?2. How old is it?