1. Do Now! 1. What are the 4 time units of the Geologic Time Scale from longest to shortest? 2. What does the law of superposition state? 3. What does the principle of cross cutting state? 4. What concept states that the forces and processes that we observe today are the same as they were in the past?

2. Radiometric Dating Radioactivity: The decay (breaking apart) of an unstable isotope (nuclei) to a more stable isotope. Radioactivity: The decay (breaking apart) of an unstable isotope (nuclei) to a more stable isotope.

3. Half-Life: The time it takes for 50% (1/2) of the nuclei in a radioactive sample to decay to its stable isotope Half-Life: The time it takes for 50% (1/2) of the nuclei in a radioactive sample to decay to its stable isotope Ex. Carbon-14 decays to carbon-12 (ALWAYS) Ex. Carbon-14 decays to carbon-12 (ALWAYS)

5. Radiometric Dating Radiometric Dating: Calculating the age of rocks and minerals that contain certain radioactive isotopes. Radiometric Dating: Calculating the age of rocks and minerals that contain certain radioactive isotopes.

6. Radiometric Dating The fraction of original isotopes indicates the number of half-lives. The fraction of original isotopes indicates the number of half-lives. Multiply the number of half-lives by the half-life time to get the age of the fossil. Multiply the number of half-lives by the half-life time to get the age of the fossil.

10. Radiometric Dating This method is possible because each radioactive isotope has been decaying at a CONSTANT rate since the formation of rocks in which it occurs. This method is possible because each radioactive isotope has been decaying at a CONSTANT rate since the formation of rocks in which it occurs. Cannot be used for sedimentary rocks because they are formed from many pieces of older rocks. Cannot be used for sedimentary rocks because they are formed from many pieces of older rocks.

11. Formatives Work quietly and independently. When you complete your exam, raise your hand, and I will collect it. Begin silently and independently working on your radiometric dating practice sheet. *This is homework if you do not complete it in class today.

12. Exit Ticket 1. What is radiometric dating? 2. What is a half-life? 3. How is radiometric dating used to determine the age of a fossil?