Radioactive Dating Chapter 7 Section 3

What Is Radioactive Decay? Most elements do not change. But some elements can break down (decay) over time. When they decay, they release particles and energy in a process called Radioactive Decay. During radioactive decay, the atoms of one element break down to form atoms of another element.

Half - Life The rate of decay of each radioactive element never changes. The time it takes for HALF of the radioactive atoms to decay is called the Half Life.

Questions: 1. What happens to the atoms of the decaying element? A. The atoms break down to form atoms of a different element 2. What else is produced during the decay process? A. Particles and energy 3. After 2 half-lives, how much of the radioactive element remains? A. 25% 4. After 3 half-lives, how much of the radioactive element remains? A. 12.5%

What Is Radioactive Dating? Radioactive elements occur naturally in igneous rocks. Scientists use the date of decay to calculate the rock’s age. Determining Absolute Ages- Scientists first determine the amount of radioactive element in a rock. Then they compare that amount with the amount of the stable element into which the radioactive element decays. Potassium-Argon Dating- Often scientists use potasium-40 to date rocks. It decays to argon-40 and has a half-life of 1.3 billion years. Its very long half-life is useful  Carbon -14 Dating- After an organism dies, the carbon-14 in its body decays and changes into nitrogen-14. To determine the age, scientists measure the amount of carbon-14 that is left. It has a short half-life (5,730 yrs)so not useful if sample is older than 50,000 yrs and its not found in most rocks 

Questions: 1. What is the first step scientists take in radioactive dating? A. Measuring amount of radioactive elements in a rock 2. What do they do next? A. Compare that amount with the amount of new, stable element being formed from the first element’s decay 3. What is an atom? A. smallest part of an element that has all properties of that element 4. What is the half-life for carbon-14? A. 5,730 yrs 5. Why is Potassium-40 more useful in dating rocks than Carbon-14? A. It has a longer half-life and it is found in most rocks