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?
