Transcript Dating methods

Fossil Dating
How do geologists determine how old rocks are?
Relative dating
Determine whether the
rock is older or younger
than other rocks
How do geologists determine how old rocks are?
Absolute dating -- use
radiometric dating techniques to
determine how long ago the rock
formed in the exact number of
years
*Not all rocks can be dated
absolutely, so combinations of
techniques are used.
Radioactive Decay, continued
• The unstable radioactive isotope is called
the parent isotope.
• The stable isotope produced by the
radioactive decay of the parent isotope is
called the daughter isotope.
• The more daughter material there is, the
older the rock is.
Radiometric Dating, continued
•
A half-life is the time needed for half
of a sample of a radioactive
substance to undergo radioactive
decay.
• After every half-life, the amount of
parent material decrease by one-half.
If the initial sample mass is
160 kg after 5 half lives how
much parent material is there
and how much daughter
material is there?
Half-life 1. 160kg divided by 2 is 80kg parent
material and 80kg daughter material present
Half-life 2. 80kg divided by 2 is 40kg parent
material and 120kg daughter material present
Half-life 3. 40kg divided by 2 is 20kg parent
material and 140kg daughter material present
Half-life 4. 20kg divided by 2 is 10kg parent
material and 150kg daughter material present
Half-life 5. 10kg divided by 2 is 5kg parent material
and 155kg daughter material present