1. Age of Rocks
Absolute Dating

2. How do we determine the age of Rocks?
Relative Dating
Age of Rocks
Radio-Active Dating
Law of Superposition
Absolute
Dating
Ordering of rock layers
Index Fossils

3. The actual age of a rock or fossil
Absolute Dating
The actual age of a rock or fossil
Absolute dating occurs through the process of radioactive dating

4. Radioactive Dating or Age
Radioactive dating is a way to measure the age of a material by comparing the amount of decayed radioactive element present in the item

5. How do scientist tell the actual age of rocks?
The universe is full of naturally occurring radioactive elements.
Radioactive atoms are inherently unstable; meaning over time, radioactive “parent atoms” decay into stable “daughter atoms.”

6. How do scientist tell the actual age of rocks?
When molten rock cools, forming an igneous rock, K40 (potassium radioactive atoms) are trapped inside.
Once formed K40 begins to decay at a predictable rate, and changing into Ar40 (Aragon).
K40 is parent atom and Ar40 is daughter cell.

7. How do scientist tell the actual age of rocks?
Scientist will measure the quantity of unstable atoms(K40) left in a rock and compare it to stable atoms(Ar40) and be able to determine the age of that sample.
Carbon is used to date once living organisms.
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8. Half-life
The amount of time required for half of the radioactive material to decay in an item or in our case the rock.

9. Half-life Rock 1st forms 100% of K40
1 half-life 50% of K40, 50% of Ar40
2 half-life 25% of K40, 75% of Ar40
3 half-life 12.5% of K40, 87.5 of Ar40
4 half-life 6.25% of K40, of Ar40
5 half-life 3.125% of K40, of Ar40

10. Half-life Chart

11. Half-Life Questions
If you have 10g of K40 and 2 half-life’s have passed how many grams of K40 do you have left?
10g of K40
1 half-life; 5g of K40
2 half-life; 2.5g of K40

12. Half-life Questions If 50% of the K40 is gone, how old is the rock?
1.3 million years old
If this rock is 3.2 million years old how much K40 is still present in this rock?
About 10%
How much Ar40 is present if the rock is 3.2 million years old?
About 90%