1. William E. Ferguson Relative DatingRelative Dating Absolute DatingAbsolute Dating

2. Kelvin Calculation of Earth Age Kelvin Calculation of Earth Age

3. Unconformity Types Unconformity Types

4. Figure 8.1 Lab

5. Folding Rock Folding Rock

6. Relative Dating Principles Relative Dating Principles

7. Geologic Puzzle Time! - superposition, horizontality, cross- cutting relationships In assigned groups of 3, work out the age relationships in Figs. 8.4 - 8.12 in your lab book In assigned groups of 3, work out the age relationships in Figs. 8.4 - 8.12 in your lab book Pay attention to contact metamorphism! Pay attention to contact metamorphism! Use pencil!!!! Use pencil!!!! Put in squiggly lines between events for uncomformities Put in squiggly lines between events for uncomformities Be ready as a group to transfer your answers to an overhead & explain your relationships to the class. Be ready as a group to transfer your answers to an overhead & explain your relationships to the class.

8. Figure 8.4b

9. Figure 8.10b

10. Figure 8.9 Lab FBKNAJDMHCLGE

11. Figure 8.10a Lab GHIABCDLFEMJK Couldbeyounger

12. Figure 8.11 Lab SJKDXEAHMRBGPF

13. Figure 8.12 Lab RNHPDATFLGJZSBEKXMOCV

14. Radioactive Decay Radioactive Decay

15. What we need to know to apply radiometric dating The half-life of a radioactive isotope = time required for half of it to decay to a stable (non-radioactive) daughter isotope. 40 K decays to 40 Ar with half-life = 1300 million years. 40 K and 40 Ar can be measured in a mass spectrometer. 40 K is decaying to 40 Ar all the time, but 40 Ar is a gas and can escape if a mineral is above the “blocking temperature”. Below the blocking temperature, 40 Ar is trapped in the mineral. If a mineral is heated above the blocking temperature, 40 Ar is lost. Different isotopes (of U, K, Rb, Sr, etc) used in dating have different blocking temperatures. 40 K has the simplest decay scheme, and is the only one we’ll examine in detail.

16. # of Parent & Daughter Atoms as a Function of Time Parent Daughter

17. Proportion of Parent Atoms Remaining as a Function of Time Fig. 10.14

18. Percent of Parent Atoms Remaining as a Function of Time

19. As more parent decays, the decay rate slows down, but the half-life doesn’t change Slope = rate of decay rate of decay Decay rate = P P = amt. Of parent = decay constant = decay constant = 0.693/half-life = 0.693/half-life