Write the name of each layer What is an important property of that

layer?

Absolute Time Radiometric or

Isotopic dating Tells an “exact” age Radioactive decay

◦ Parent nucleus becomes more stable daughter nuclei

◦ Give off energy◦ Constant rate

Half-life◦ 100g → 50g + 50g◦ → 75g + 25g

% parent left = # of half-lives → age What do we use?

◦ Carbon-14◦ Uranium-235◦ Potassium-40

Carbon Dating Various forms of carbon

◦ Most common = carbon-12

◦ Radioactive = carbon-14 Carbon-14

◦ Used for things that were alive

◦ During life - constantly replaced

◦ After death - amount starts to decrease

◦ Half-life of 5,730 years

Half-Life Fraction carbon -14 left

Percentage carbon-

14 left

Age

1

2

3

4

You are a CSI Detective…• You found a skeleton 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?