Absolute Age find actual date of the event

Absolute Age • find actual date of the event: 1. Tree Rings & Varves 2. Radioactive Decay

Radioactive Decay • rocks contain radioactive elements. These elements give off particles and energy they will eventually form new nonradioactive elements.

Radioactive Decay • Compare the amount of radioactive and nonradioactive elements to predict the absolute age of a specific rock

Examples: • Uranium is found in rocks • U-238 will decay to form U-234 (releases 2 protons & 2 neutrons) • It will eventually decay all the way to produce Pb -206

Examples: • U-238 = parent element • Pb-206 = daughter element

Half-Life • The decay of U-238 to Pb -206 is a very slow process. • Rate of decay is constant • It takes 4. 5 billion yrs for half of U-238 to decay

Half-Life • In conclusion = the more Pb-206 in a rock the older it will be.

Carbon Dating • C-14 is a radioactive element found in ALL living things. • When plant/animal dies C-14 decays to form N-14 • The half-life of C-14 is about 5, 730 years

Living Organism C-14 Organism Dies No New C 14 5, 730 yrs later 50% C-14 11, 460 yrs later 25% C-14

Let’s take some time to practice learning what is meant by an element’s half-life

• • If an organic fossil has ½ of its original carbon remaining, how many years ago did it die? If something has been dead 17, 100 yrs, how much carbon would it still have remaining? How much carbon-14 would something have left if it had been dead 22, 800 yrs? If a fossil has only one quarter of its carbon remaining, how many years ago was it alive?