1. Absolute Dating

2. Absolute Dating
Absolute Dating determines the actual age of a rock or fossil in years.
The main method of absolute dating is RADIOMETRIC DATING.

3. How Radiometric Dating Works
Radioactive elements are elements with atoms that give off particles (radiation) from their nuclei. This is called Radioactive Decay.
Atoms give off particles to become new lighter, more stable elements. Decay will continue until the new element is stable and not radioactive.

5. Rate of Decay
Radioactive elements decay at CONSTANT RATES. As soon as a rock forms with radioactive elements in it, decay begins. We use this to find the age of a rock.
The rate at which an element decays into a new element is measured as a HALF LIFE.

6. Half Life
A HALF LIFE is the amount of TIME it takes for HALF of atoms of a radioactive element to decay into a new, stable element.
Terms used to describe material:
Parent Material: the original, radioactive element
Daughter Material: the new, stable element

7. Half Life Example 100 % Parent Material Time= 0 The rock formed
50 % Parent, 50% Daughter 1 Half Life
25% Parent, 75% Daughter 2 Half Lives
12.5 % Parent, 87.5 % Daughter 3 Half Lives
6.25% Parent, % Daughter 4 Half Lives

9. Graph of data: Decay Curve
100
% Parent 50 25
12.5
6.25 1 2 4 5 3
Half Lives

10. Using Half Life to find Age
If you know the number of years there are in an element’s half-life, you can figure out the age of a rock.
The number of years in an elements’ half-life would be the number of YEARS it takes for HALF of the radioactive elements in the rock to turn into stable elements.

11. Example The number of years in a half-life for Carbon-14 is 5,730.
So….. If one half-life has passed, the rock is 5,730.
If two half-lives have passed, the rock is 11,460 years old.

12. Samples of Half-Lives

13. Questions
If a rock contains 50% parent material, how many half-lives have passed?
If a rock contains 12.5 % parent material, how many half-lives have passed?
If a rock’s half-life is 25 years, and two half-lives have passed, how old is the rock?
If a rock’s half-life is 50 years, and three half-lives have passed, how old is the rock?

14. Half Life, 1/2