Tuesday, November 15 th, 2011 Bell Ringer: In your science notebooks, answer the following question: “How do you think the half life of a radioactive element, like Uranium, helps us date rocks?” Today’s Learning Goal: How do we assign numerical ages to rocks, and ultimately, the earth? Today’s Agenda: Introduction to Radioactive Decay Age Dating Activity

Part of an AtomMass (amu)Charge Electron0 Proton1+1 Neutron10 Review the Atom

3 Types of Radioactive Decay Alpha Decay Beta Decay Gamma Decay 9yt7OAYmE

Half-Life The time it takes for half the radioactive atoms to decay to the more stable isotopes To find the age of a substance: #half-lives X half-life of the element = AGE Ex: 1.2 half-lives X 704,000,000 years= 844,800,000 years old

Half-Life

Half- Life Table 1Table 2Table 3Table 4Table 5Table 6Table 7Table 8Table 9 Table 10 Table 11 Table 12 Ave

Half-Life % Predicted Atoms Remaining % Parent Isotopes Remaining ( 14 C) % Daughter Isotopes ( 14 N) 0100% 150% 225% 312.5% 46.25% Table 2. Number of Parent to Daughter Isotopes

Trilobite Fish Reptile Saber-toothed Tiger

Fossil % Uranium- 235 % Lead-207 Trilobite60%40% Fish75%25% Reptile85%15% Saber-toothed Tiger95%5% Dr. Limestone’s Data

Calculate the Age of the Fossils To find the age of a substance: #half-lives X half-life of the element = AGE

Exit Card: No Exit Card Today Tomorrow’s Learning Goals: How do we assign numerical ages to rocks, and ultimately, the earth? Exploration of Earth’s Past!