The Age of the Earth

1. The Age of the Earth David E. Thomas PSY 131 Tuesday, March 20th, 2018 dthomas@passcal.nmt.edu 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. 50% 25% 12.5% 6.25% Radioactive Decay

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

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

8. Top Three Creationist Critiques

9. Top Three Creationist Critiques Answer: Nuclear Isochrons

10. Answer #1: Nuclear Isochrons

11. Nuclear Isochrons – 3 Isotopes are Needed (87Rb=>87Sr, also86Sr) 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. Slope=0, T=0: Uniform Mixing of both Sr isotopes at the time of solidification Isochron Slope → Sample Age 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 4.53 +/- 0.16 whole rock Ar-Ar 4.49 +/- 0.06 Saint Severin 4 samples Sm-Nd 4.55+/- 0.33 10 samples Rb-Sr 4.51 +/- 0.15 whole rock Ar-Ar 4.43 +/- 0.04 whole rock Ar-Ar 4.38 +/- 0.04whole rock Ar-Ar 4.42 +/- 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, = 18.18 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. Line cuts curve on right: time since rock formed from melt. Line cuts curve on left: time since heating event. Concordia/Discordia U-Pb concordia- discordia diagram for nine samples of the 3.56 billion-year-old Morton Gneiss, Minn. After Goldich and others

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% ~ 0.00715 Ancient ratio (1.7BYA) of U235/U238: 2.9% ~ 0.029 Add Water (Moderator) ...

37. 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?