# Activity 8 3 absolute dating of rocks and fossils At the end of the lesson each student will be presented with his/her own fossil.This fossil will have information containing how much of the parent and daughter isotopes were found as well as the accepted half-life of the radioactive isotope.This lesson is designed to help students understand the concepts of radioactive dating to help determine the approximate age of fossils and rocks.After this lesson students will have an understanding of how materials undergo radioactive decay and that the rate of decay allows scientists to predict the approximate age of the specimen.

Before the lesson the teacher will need to make a student activity worksheet with the data table, graph, and follow-up questions found on the website.Using a graph that relates percentages of parent isotope levels to number of half-lives students will determine the approximate age of the fossil.Example data set: Potassium-40 = 12 isotopes Argon-40 = 88 isotopes Half-life = 1.25 billion years Answer: Using the graph from the Exploration activity, this radioactive isotope has undergone three half-lives thus making the fossil (1.25 * 3 =) 5.25 billion years old.The statistical probability of the M&M "decay" is 50% per each half-life but the actual data may not reflect the theoretical probability.Students may confuse this random change of events with the non-random decay of radioactive isotopes.   Make sure to know any food related allergies of the students before handing them the candy.

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1. For example, JJA Worsaae used this law to prove the Three Age System.