1. TIME

2. PRS
Figure out at what time you put on your shoes this morning (assuming you are wearing shoes). What dating technique did you use?
A. Numerical Time B. Relative Time C. both

3. PRS
Which type of time reckoning do you use most often?
A. Numerical Time B. Relative Time

4. Bishop Ussher – Earth formed 4004 B. C
Bishop Ussher – Earth formed 4004 B.C. –October 23 – using Biblical history
GROUP QUESTION: Think of another way to come up with a minimum age for the earth (do not use radioactivity)

5. Uniformitarianism - James Hutton "no vestige of a beginning, no prospect of an end."
“The present is the key to the past”
But rates of processes change – so only things that are constant are physical laws.

6. Original Horizontality
Superposition
Crosscutting Relationships
Inclusions

7. Group Question
Using your experience with sediments, like the sand on a beach, is there a problem with Steno’s Principle of Original Horizontality? If so, what?

8. Unconformities

9. Group Question
Going back to your beach, is there an unconformity there?
Most of Geologic time is represented by unconformities

10. Crosscutting Relationships
Inclusions

11. Which is older
Dike A
Dike B
Fault
Dolostone
Sandstone B

12. William “Strata” Smith
Engineer
Surveyor
Biostratigrapher

13. William “Strata” Smith 1769-1839: canal engineer, first stratigrapher

14. Wm. Smith’s canals today

15. Geologic Time Scale
Pieced together through correlation
Dates come from radioactivity

16. Relative Time vs. Absolute (Numerical) Time
Bishop Ussher – Earth formed 4004 B.C. –October 23 – using Biblical history
GROUP QUESTION: Think of another way to come up with a minimum age for the earth (do not use radioactivity)

17. Atoms

18. Isotopes 6 protons 6 protons 6 protons
6 neutrons 7 neutrons 8 neutrons

19. PRS
If an atom with 19 protons and 20 neutrons is an isotope of Potassium,
Which of the following is another isotope of Potassium?
20 p, 19 n
20 p, 21 n
19 p, 22 n
20 p, 22 n
18 p, 22 n

20. Radioactivity
Parent Daughter

21. Need to know 4 things
Sample had some parent at start
Sample has been “closed system”
Decay rate of parent-daughter pair
Parent-daughter ratio at start
Need to measure 1 thing
Parent-daughter ratio now

23. Industrial revolution added C12 – diluting the C14
Nuclear Bomb Tests added C14

24. C14 Calibration

25. Why don’t geologists use 14 C to date rocks?
Half life is too long
Rocks aren’t closed systems
Rocks don’t have any Carbon
Rocks don’t get carbon from atmosphere
Rocks have too much 14 C

26. K – Ar dating
HL 1.26 BY
Daughter is noble gas

29. (compiled from Dalrymple, 1991)
Technique
Age Range (billion years)
uranium-lead
3.60±0.05
lead-lead
3.56±0.10
3.74±0.12
3.62±0.13
rubidium-strontium
3.64±0.06
3.62±0.14
3.67±0.09
3.66±0.10
3.61±0.22
3.56±0.14
lutetium-hafnium
3.55±0.22
samarium-neodymium
3.56±0.20
(compiled from Dalrymple, 1991)

30. Geologic Time Scale
Pieced together through correlation
Dates come from radioactivity

31. Correct answer for 8.3
Youngest J E C A G B I D F H
Oldest