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)

3. ESSENTIAL QUESTION
How do scientists use absolute dating to build a model of the Earth’s history?

4. ABSOLUTE DATING

5. Isotopes
All atoms are isotopes!!! Number of protons stay the same Number of neutrons changes

6. Isotopes
Example: 14C and 12C Both have 6 protons, but 14C has 8 neutrons where 12C only has 6

7. Radioactivity Some atoms are not stable
These atoms emit particles to achieve stability

8. Radioactivity There are three types of particles emitted
Alpha particles
Beta Particles
Gamma Rays

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

10. Beta Particles Charge = -1 Mass = negligible
Small, more penetrating particle, but still easily stopped

11. Beta Particles Neutron decays Electron leaves nucleus
Atomic number goes up 1

12. Gamma Rays Pure energy No change in atom
Very penetrating, but cause little damage

13. ABSOLUTE (RADIOMETRIC) DATING
Based on decay rates of different atoms
Rate of decay stated as half- life

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

15. Half-life Atoms used in geologic dating have long half-lives
Parent Daughter Half-life
Uranium-238 Lead ,470 million years
Uranium-235 Lead million years
Potassium-40 Argon ,250 million years
Rubidium-87 Strontium ,800 m. y.
Carbon-14 Nitrogen-14 5,730 years

16. Half life Scientists use both decay and production curves
© The Geological Society of America, 2003
Scientists use both decay and production curves

17. Assigning Ages
Using the proportion of daughter atom in a sample, its age can be determined

18. Major Principle of Absolute dating

19. CHECK FOR UNDERSTANDING
Explain the main concepts of how scientists use absolute (radiometric) dating to determine the age of objects.