Radioactive Dating (pages 323–326) 1. Explain what happens during radioactive decay. 2. Describe what can be learned from radioactive dating. Radioactive Decay (page 324) 1. Explain what happens during radioactive decay. Key Concept: During radioactive decay, the atoms of one element break down to form atoms of another element. Everything is made up of one or more pure substances. These pure substances are called elements. Some elements break down, or decay. When an element decays, it changes into another kind of element. The process is called radioactive decay. Elements that decay are called radioactive elements. Potassium-40 is an example. Potassium-40 decays into argon-40. How fast an element decays is given by its half-life. The half-life is the time it takes for half of a sample of an element to decay. For example, the half-life of potassium-40 is 1.3 billion years. Determining Absolute Ages (pages 325–326) 2. Describe what can be learned from radioactive dating. Key Concept: Geologists use radioactive dating to determine the absolute ages of rocks. Scientists test rocks to measure how much radioactive decay has happened. The more decay that has happened, the older the rocks is. This method of dating rocks is called radioactive dating. Using this method, scientists can give rocks a rough age in years. When age is given in years, it is called absolute age. Suppose that half of the potassium-40 in a rock has decayed to argon-40. The half-life of potassium-40 is 1.3 billion years, so the rock is about 1.3 billion years old. Radioactive dating works well for igneous rocks. But this kind of dating does not work well for sedimentary rocks. This is because sedimentary rocks are made of rock particles of different ages.
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