1. The Age of the Earth David E. Thomas PSY 131 Tuesday, March 20th, 2018
Week 9, Lecture 17

2. Thought of the Day
“Deep Time is like an endless, dark corridor, with no landmarks to give it scale. This darkness is occasionally pierced by a shaft of light from an open door. Peering into the lighted room, we see a tableau of unfamiliar characters from the lost past...” - Henry Gee

3. Radiometric Dating – The Most Accurate Method We Have
Nuclear decays occur at energies much higher than chemical reactions, and are by and large not affected by huge pressure, chemical or temperature variations. P D

4. Radioactive Decay

5. Radioactive Decay
50%
25%
12.5%
6.25%

6. Ratio of Daughter/Parent=Time
Young
Old
But, what if some Daughter was present at “Time Zero”?

7. Or, What if Daughter Escapes the System to the Outside?
D D

8. Top Three Creationist Critiques

9. Top Three Creationist Critiques
Answer: Nuclear Isochrons

10. Answer #1: Nuclear Isochrons

11. Increasing Strontium (Daughter)
Nuclear Isochrons – 3 Isotopes are Needed (87Rb=>87Sr, also 86Sr)
Minerals with more Rubidium produce more Strontium in a given time.
87Sr/86Sr
Increasing Strontium (Daughter)
At T =1 Halflife, slope = 45o
Increasing Rubidium (Parent)
87Rb/86Sr

12. Nuclear Isochrons - @ Melting
On melting and mixing, all isotope ratios equalize. This is key to how isochrons work.

13. Nuclear Isochrons – Valid Sample
This is the 3 BY evolution of the isochron chart for a valid sample (melted at time 0).

14. Nuclear Isochrons – Valid Sample
Isochron at 1 BY for a valid sample (melted at time 0).

15. Isochron Slope → Sample Age
Slope=0, T=0: Uniform Mixing of both Sr isotopes at the time of solidification
87Sr/86Sr
Slope + 1 = 2(# Half-Lives)

16. Nuclear Isochrons – Invalid Sample
This is the 3 BY evolution of the isochron chart for an invalid sample (not from a melt).

17. Nuclear Isochrons – Daughter Lost
This is the 3 BY evolution of the isochron chart for an invalid sample (Daughter product removed at 1 BY).

18. Nuclear Isochrons - Summary
Valid
Slope => Age, intercept = initial Daughter amount
Invalid – daughter loss
Invalid – not melted

19. Nuclear Isochrons - Summary
They provide a robust estimate of the age of the sample as a fit of many data points.
They provide a precise measure of the amount of initial daughter product.
They include Quality Control that shows if the sample should not be used because of conglomeration instead of melting, or because of loss of daughter or parent.

20. Radiometric Dating→Old Earth
When you get the same time estimates from very different clocks, that increases your confidence in the estimates.

21. Radiometric Dating → Old Earth
Dating Molten Planets - Meteorites
Olivenza 18 samples Rb-Sr /- 0.16
whole rock Ar-Ar /- 0.06
Saint Severin 4 samples Sm-Nd 4.55+/- 0.33
10 samples Rb-Sr /- 0.15
whole rock Ar-Ar /- 0.04
whole rock Ar-Ar / whole rock Ar-Ar /- 0.04
Rb-Sr 48.8 BY; Ar-Ar 1.25 BY; Sm-Nd 106 BY

22. Now for something Really Cool…
The Isochron Method informs us when a sample is not useful for geochronology. But, there isn’t a way to get an answer in such cases.
What if a method could tell if a system hasn’t always been closed, and could also provide the age, even for systems with profound daughter losses (open system)?

23. Top Three Creationist Critiques

24. Top Three Creationist Critiques
Answer: Concordia/Discordia

25. Concordia/Discordia - Method
4 isotopes are required: U235 and its daughter Pb207(halflife=704 MY), and U238 and its daughter Pb206(halflife=4.47 BY).
At 3BY, “X” value = ratio of Pb207 to U235, = and only 5.2% of original U remains
At 3BY, “Y” value = ratio of Pb206 to U238, = 0.59

26. Concordia/Discordia - Valid
This is the 5 BY evolution of the concordia chart for a properly melted sample (no lead at start-up!).

27. Concordia/Discordia – Heating Event
At 3 BY, things really heat up. (Volcanic intrusion, perhaps.)

28. Concordia/Discordia – Heating Event
During this brief heating episode, Lead is expelled in equal proportions for both isotopes.
17% lost
33%
50%
67%
83%
100%

29. Concordia/Discordia – Heating Event
This is the 5 BY evolution of the isochron chart for the 3BY/heated sample.

30. Concordia/Discordia – Heating Event

31. Concordia/Discordia
Line cuts curve on right: time since rock formed from melt.
U-Pb concordia- discordia diagram for nine samples of the 3.56 billion-year-old Morton Gneiss, Minn. After Goldich and others
Line cuts curve on left: time since heating event.

32. Top Three Creationist Critiques

33. Top Three Creationist Critiques
Answer: Oklo Natural Nuclear Reactor

34. Answer #3: What if Decay Rates were not Constant?
Rates slightly affected by, say, pressure do not usually involve methods used to date the Earth (K-Ar, K-capture, ‘no detectable effect’).
Even if they were, the changes are small (typ. <1%), and would not change the great age of the Earth.

35. Natural Nuclear Reactor: Oklo
Gabon, West Central Africa; discovered in 1972
1.7 BYA; yield about 100 KW

36. Natural Nuclear Reactor: Oklo
U238: half life = 4.47 billion years
U235 : half-life = 704 million years
Modern day ratio of U235/U238: 0.71%/99.28% ~
Ancient ratio (1.7BYA) of U235/U238: 2.9% ~ 0.029
Add Water (Moderator) ...

37. Confirmation of the Uniformitarian Hypothesis
The Moral of Oklo
Fission tracks from almost two billion years ago indicate that atomic decay processes have remained unchanged in all that time.
Confirmation of the Uniformitarian Hypothesis

38. More Confirmation of the Uniformitarian Hypothesis
Speed of Light: Measurements of Supernova SN1987A allow (A) Determination of the distance via trigonometry on the effect of UV rays on gas rings surrounding the star, independent of light speed; and (B) calculation of half-lives of cobalt-56 and cobalt-57 from the intensity changes. If Light were traveling faster 168,000 years ago, than those decays would appear slowed down. They don't. Confirmation that both decay rates and lightspeed have remained constant. Link

39. More Confirmation of the Uniformitarian Hypothesis
Methanol: Methanol (CH3OH, the simplest form of alcohol) is sensitive to changes in the proton-electron mass ratio. A small deviation would affect the structure of the molecule and the associated absorption spectrum. … If the proton-electron mass ratio changes, some lines in the methanol spectrum will strongly shift while others will remain the same (the so-called anchor lines). A research team led by FOM workgroup leader Prof. Dr. Wim Ubachs and Dr. Rick Bethlem has once again demonstrated that the mass ratio between electrons and protons has remained the same over the past 7.5 billion years. LINK.

40. Conclusion
Scientific data clearly show the Earth is ~ 4.54 Billion years old …
Creationist attempts to prove the Earth is Young are flawed by errors, disregard of contrary evidence, & over-simplified models…
Please -- can we just have a little respect for our Elders?