Igneous RocksFormation, Absolute

Age, Radioactive Dating and Unconformities

What is an Igneous Rock?

• AKA: Fire Rocks •Can be formed underground or above ground:•Underground - formed when melted rock called magma•Aboveground - formed when volcanoes erupt

What does an Igneous Rock look like?

Granite Pumice

Determining the Age of an Igneous Rock

•Think back….How did we determine the age of a sedimentary rock? •Can we use the same method for Igneous Rock?•Why or Why not?

•Absolute Age – the process of determining a computed, numerical age

Relative vs. Absolute Age

•Turn to your shoulder buddy…•Quickly discuss the differences between relative and absolute age

Determining Absolute Age

Radioactive Dating – using radioactive particles found in a rock to determine the actual age of the rock

Radioactivity – the process of rock elements breaking down

You can only find these radioactive particles in igneous rocks (does not work with sedimentary rock)

Technology Used to Measure Radioactivity

Geiger Counter Ionization

Chamber

MicroR Meter

JapanRadioactive waves can be harmful to our health

Determining Absolute Age

Half-life: The breakdown of specific elements happens at a very specific pace•Examples: •Carbon-14 has a half-life of 5,730 years.

•Always found in LIVING organisms•Potassium-40 has a half-life of 1.3 billion years

•Using a specific calculation can help you determine the absolute age using half-lives

Determining Absolute Age

Half-life: The breakdown of specific elements happens at a very specific pace•Examples: •Carbon-14 has a half-life of 5,730 years.

•Always found in LIVING organisms•Potassium-40 has a half-life of 1.3 billion years

•Using a specific calculation can help you determine the absolute age using half-lives

Visuals Help with Radioactive Decay

Original Rock

1 Half Life 2 Half Lives 3 Half Lives 4 Half Lives

Practice Time!!!Percentage of Radioactive

Material in Rock

Number of Half Lives

100% - 50% 150% - 25% 2

25% - 12.5 % 3

12.5% - 6.25% 4

6.25% - 3.126% 5

Element Brennan is found in an igneous rock and we are trying to determine the rocks age. We know Brennan’s half life is approximately 3,000 years and that the rock is currently 25% radioactive. How old is the rock?

75% decayed

94% decayed87.5% decayed50% decayed

50%Radio- active 25% r-a

12.5%6%

100% Radioactive Igneous Rock

One Half Life Two Half Lives Three Half Lives Four Half Lives

Element Brennan is found in an igneous rock and we are trying to determine the rocks age. We know Brennan’s half life is approximately 3,000 years and that the rock is currently 6.25% radioactive. How old is the rock?

Element Brennan is found in an igneous rock and we are trying to determine the rocks age. We know Brennan’s half life is approximately 3,000 years and that the rock is currently 50% radioactive. How old is the rock?

LAST PRACTICE QUESTION!!!

Last Practice Question:A rock contains a radioactive element with a half life of 100 million years. Tests show that the element in the rock has gone through three half lives.

How old is the rock?

Ticket Out the Door• Make a Venn Diagram to compare and

contrast absolute and relative age.– Which does radioactive decay fall under?– Which does law of superposition fall under?