1. Finding Absolute Age Radioactive Decay -Nuclei of some isotopes are unstable -The parent material decays and gives off particles (decay products) http://www.physics.carleton.ca/~watson/1000_level/Recent_Physics/Gifs/Uranium_decay.gif

2. Radioactive isotopes -found in the minerals that crystallize when rocks form -as time goes on amount of parent material ___creases and amount of decay products ___creases - Decay rate of each isotope is known - Can use the ratio to determine age This method of determining age is called radioactive dating.

3. Half-Life Half Life – The amount of time required for half the radioactive nuclei in a sample to decay.

4. Isotopes used for Finding Ages -Carbon-14 only present in organic (once living) material-can’t be used for igneous rocks (not in lava) -no contamination (chemical weathering) Argon 40 is a gas-can escape.

6. -Isotopes with short half-lives good for only “young” rocks -Those with long half-lives good for only “very ancient” rocks Do “Review 12.4” on page 274 of text.

7. For igneous rocks (eg. granite), and metamorphic rocks, radioactive dating shows the age of the rock since the crystals actually formed. (eg. cooling of magma) Sedimentary Rocks are formed from the weathered grains of much older rocks. Radioactive dating gives the age of the older rocks, not the sedimentary ones!

9. Do Activity 12F on pages 275-277 of Textbook.