1. Introduction to Absolute (Radiometric) Dating

2. Learning Targets 4a) I can distinguish between absolute and relative dating. (DOK 1) 4b) I can define what an isotope is and describe how radioactive isotopes decay (DOK 1) 4e) I can identify and analyze key strengths and limitations of using radioactive decay in absolute dating. (DOK 1-2) Essential Question How do scientists use absolute dating to build a model of the Earth’s history?

3. Absolute Dating

4. Isotopes Two or more of the same element with different masses. Have the same number of protons but number of neutrons changes. http://education.jlab.org/glossary/isotope.gif

5. Isotopes http://www.radtrainonline.com/free/viewslide.asp?CourseID=92&ModuleID=353&SlideID=6291

6. Radioactivity o Some atoms are not stable o These atoms emit particles to achieve stability http://abyss.uoregon.edu/~js/images/radioactivity.gif

7. Radioactivity There are three types of particles emitted: 1.Alpha particles 2.Beta Particles 3.Gamma Rays

8. Alpha Particles o Charge = +2 (2 protons) o Mass = 4 (2 protons + 2 neutrons) o Large, easily stopped by paper © The Geological Society of America, 2003

9. Beta Particles o Charge = -1 o Mass = negligible o Small, more penetrating particle, but still easily stopped http://sol.sci.uop.edu/~jfalward/elementaryparticles/betaparticleenergy.JPG

10. Beta Particles o Neutron decays into a proton and an electron o Electron leaves o Atomic number goes up 1 http://sol.sci.uop.edu/~jfalward/elementaryparticles/betaparticleenergy.JPG

11. Gamma Rays o Pure energy o No change in atom o Very penetrating, cause damage http://www.arpansa.gov.au/images/basics/all_pen.jpg

12. Absolute (Radiometric) Dating o Based on decay rates of different atoms o Rate of decay stated as half-life http://www.bible.ca/tracks/dating-radiometric-cartoon.gif

13. Half-Life Time it takes for ½ of the radioactive atoms to decay into its daughter atoms © The Geological Society of America, 2003

14. Half-Life Atoms used in geologic dating have long half- lives ParentDaughterHalf-Life Uranium-238Lead-2064,470 million years Uranium-235Lead-207704 million years Potassium-40Argon-401,250 million years Rubidium-87Strontium-8748,800 m. y. Carbon-14Nitrogen-145,730 years

15. Half-Life Scientists use both decay and production curves © The Geological Society of America, 2003

16. Assigning Ages Using the proportion of daughter atom in a sample, its age can be determined http://upload.wikimedia.org/wikiversity/en/thumb/4/4b/Radiometricdatingmineral.png/400px-Radiometricdatingmineral.png

17. Major Principle of Absolute Dating

18. Check for Understanding Explain the main concepts of how scientists use absolute (radiometric) dating to determine the age of objects