1. ABSOLUTE AGE
Absolute dating- used to determine the age of a rock or fossil
more exactly based on the properties of atoms
An atom:

2. In an atom, protons ( + ) and neutrons (neutral)
are found in the nucleus.
Electrons ( - ) are found in orbitals around the nucleus.
Every element has an exact number of protons, neutrons and
electrons in order to be stable.

3. An isotope is the same element with a different
number of neutrons.
Atomic mass - number of protons and neutrons combined
Radioactive decay - the number of protons in an atom is changed;
forms a new element
Ex. - If parent material is Uranium (atomic mass 238),
And the daughter material is lead ( atomic mass 206);
caused by a loss of 32 protons after a long series of decay
(Lead is not radioactive and will not decay any further.)

4. Each radioactive parent material has a certain rate at which it
decays to its daughter material.
Half-life -the time it takes for half of the atoms of the isotope
to decay.
Ex.- half -life of Carbon 14 is 5730 years, so it will take 5730
years for half of the C-14 in an object to become nitrogen-14

5. The Half-life of Bismuth

6. How can knowing the half-life of Carbon-14 help scientists
find out the age of a fossil?
Radiometric dating - measure amounts of parent/daughter
materials; if know half-life of material and original amount,
Can calculate absolute age
Carbon-14 is useful for dating rocks and fossils up to 75,000
years old. Uranium 238 is used for older objects.
Based on radiometric dating, the age of the earth is estimated
to be 4.6 billion years.

7. Try this example problem:
An object is found to contain 2 grams of C-14. A similar bone
(from today) is found to contain 4 g of C-14.
Approximately how old is the bone?