Absolute Age: the actual age of an object
How?
radioactive decay
The breakdown of a radioactive isotope into
a stable isotope of the same element or a
another element
Let’s take a trip down memory lane….
8
O
Oxygen
15.999
Electrons in energy
levels
Protons and Neutrons in the nucleus they make up the atomic mass
Isotopes
When the number of neutrons change, we
have an isotope. These isotopes can be
stable or unstable. If they are unstable, a
neutron will most likely convert to a proton
resulting in a different element
This happens
at a constant
rate
Parent
Isotope
Daughter
Isotope
In units of time (years)
When half of the
radioactive
sample decays,
that is a halflife.
How much (%) of a parent isotope
is left after 1 half-life?
50%
How much (%) of a parent isotope
is left after 2 half-lives?
25%
How much (%) of a parent isotope
is left after 3 half-lives?
12.5%
How much (%) of a parent isotope
is left after 4 half-lives?
6.25%
We use half-lives to determine age through
radiometric dating
Sample Problem: A
crystal contains a
radioactive isotope with
a half-life of 10,000
years. 25% of the
parent isotope remains.
how old is the sample?
Answer:
25% remains, so….
2 half-lives
10,000 x 2 = 20,000 years