Absolute Dating. How do we determine the age of Rocks? Age of Rocks Relative Dating Absolute Dating...

Absolute Dating

Age of Rocks

How do we determine the age of Rocks?

Age of Rocks

Relative

Dating

Absolute

Dating

Law of Superpositio

n

Ordering of rock

layersIndex Fossils

Radio-Active Dating

•The actual age of a rock or fossil•Absolute dating occurs through the process of radioactive dating

Absolute Dating

Radioactive dating is a way to measure the age

of a material by comparing the amount of

decayed radioactive element present in the

item

Radioactive Dating or Age

• 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.”

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.

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.

• http://www.youtube.com/watch?v=vYvUSro7YUM

How do scientist tell the actual age of rocks?

• The amount of time required for half of the radioactive material to decay in an item or in our case the rock.

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, 93.75 of Ar40

• 5 half-life 3.125% of K40, 96.875 of Ar40

Half-life

Half-life Chart

1. 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

Half-Life Questions

1. If 50% of the K40 is gone, how old is the rock?

• 1.3 million years old

2. If this rock is 3.2 million years old how much K40 is still present in this rock?

• About 10%

3. How much Ar40 is present if the rock is 3.2 million years old?

• About 90%

Half-life Questions