ELIMINATING STUDENTS' MISCONCEPTIONS OF RADIOACTIVE DECAY AND RADIOMETRIC DATING THROUGH HANDS-ON ACTIVITIES

Radioactive decay and radiometric dating are fundamental Earth Science principles. It is essential for students to have a solid understanding of these concepts because accurate dating of rocks and organic remains enables us to better understand Earth processes, deep time and the evolution of life on Earth. Students often have difficulty comprehending these topics and hold a variety of misconceptions. Specific examples from our experience include: absolute dating provides error-free ages; decay rates could be affected by the sample age, composition or environment; radioactive isotopes decay into nothing; half-life is half the life of an atom; and half lives are the same for all atoms. These questions, coupled with the complex effects of metamorphism and element mobility, stand in the way of understanding Earth evolution.

The first two authors developed a unit to correct 8th grade students’ misconceptions and to foster interest in radioactive decay and radiometric dating. The unit began with an introductory lesson on radioactive isotopes, followed by two days of hands-on small group activities that developed critical thinking, math and graph making/interpretation skills. First, students visualized the concepts of radioactive decay and half-life in an activity using M&Ms™ and marshmallows. M&Ms™ were shaken in a bag, poured out on the table, and then removed to the decayed pile if they did not show their “m” label. As parent element M&Ms™ were removed through radiometric decay, daughter element marshmallows replaced them. Later, students applied this knowledge to determine the ages of a series of rocks and organic remains represented by bags of Froot Loops™. Various colors were used to indicate parent and daughter isotopes of several elements with different half-lives. For each sample, students worked to identify the number of half-lives that had passed since the time of sample formation and its current age. This activity enabled visualization of the change from one isotope to another and the amount of time involved.

Students reported that their knowledge was enhanced and their misconceptions were addressed. Some commented specifically that food made the activity more accessible on a sensory level. This use of varied modalities for learning gives benefit to a wide range of student learning styles.