EES 1030 Lecture 13: 13

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Earth & Environmental Sciences
EES 1030
John Adrain

EES:1030 Geologic Time and Rock Rules II March 02nd, 2017 Study Guide Questions 1. What is the difference between absolute and relative dating of Earth materials 2. What is an isotope? 3. Why do some isotopes decay , and what are the different kinds of decay processes? You should be able to recognize their names. 4. Be comfortable with using the table given in the handout to infer absolute ages, and to decide which isotope pairs are most useful for dating different materials. 5. After 4 half lives, how much parent m aterial () would you expect there to be remaining? Daughter material? 3 half lives? You should be able to infer ages of different materials, given proportions of parentdaughter material. 6. Why cant we radiometrically date material infinitely (for example, why cant you use carbon dating for material that is 150,000 years old)? 7. What happened in Chelyabinsk, Russia, on February 15 th2013? 8. What big assumptions do we make when we utilize radiom etric dating? 9. What is the best material for radiometric dating, and why? You should be able to talk about closure temperature. 10. How have we estimated the age of the Earth? . Radiometric dating: how we put absolute dates on things. What we use: radioactive isotopes. Remember, our atomic number is defined by the number of protons, but our mass number is defined by the number of neutrons in an atom. You can have extra neutrons and still be the same element. Isotope basics: an isotope of an element has the sa me number of ______________ _________ but a different number of __________________ ______. Many isotopes are not radioactive . Some isotopes, however, are radioactive! They will change over time into a new form. Why they do this: 1. Parent isotopes have unstable nuclei: this makes them radioactive. 2. Unstable isotopes change spontaneously to become another isotope of the same element, or a different element. They lose energy in the process and become more stable. This can happen via alpha decay, beta decay, or electron capture (you do not need to know the details of these processes). Half lives: PROPORTION of parent atoms that turn into daughter atoms is the same in each half life: we always lose half of whatever we start the individual half life with. So i f you started with 1,000 parent atoms, after 1 half life you would have 500 parent atoms and 500 daughter atoms. After 2 half lives you would have 250 parent atoms and 750 daughter atoms (NOTE: we lose half of the remaining parent with each time step!) Radiometric dating stops being possible eventually because... Very important table that I want you to be able to use: Parent and Daughter Half life Dating range Carbon 14Nitrogen 14 5,730 years 10030,000 years Potassium 40Argon 40 1.3 GA 100,0004.6 GA Rubidium 87Strontium 87 47.0 GA 10 M4.6 GA Uranium 238Lead 206 4.5 GA 10 M4.6 GA Uranium 235Lead 207 730 MY 10 M4.6 GA 1
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