1. Marmota monax

2. 12 hr Daylight 12 hr Night Groundhog Day cross-quarter 12 hr Daylight 12 hr Night Shortest Day Longest Day Halloween cross-quarter May Day cross-quarter Lughnas cross-quarter

3. Radiometric Age Dating

4. Requirements for a geologic clock: Begin at the time a rock was formed Operate at a constant rate Not be influenced by other processes (not rain, cold, dark of night) Radiometric Age Dating

5. Conditions met by: RADIOACTIVITY Radiometric Age Dating

6. Conditions met by: RADIOACTIVITY Radiometric Age Dating What is it?

7. Review of chemistry fundamentals: Rock: composed of one or more minerals Mineral: composted of one or more elements Molecule: multiple atoms Atom: smallest particle of an element. Radiometric Age Dating

8. Example: Table Salt is made of two elements Sodium & Chlorine (Na Cl) solid Radiometric Age Dating

9. Example: Table Salt is made of two elements Sodium & Chlorine dissolved in water (Na+ and Cl-) Radiometric Age Dating

10. Example: Radiometric Age Dating

11. Why is Gold a shiny yellow metal? Radiometric Age Dating http://www.cupel.com/copyright/gold_ingots.jpg

12. Radiometric Age Dating Elemental properties are dictated by the number of subatomic particles:

13. Elemental properties are dictated by the number of subatomic particles: Radiometric Age Dating Specifically the number of protons in the nucleus.

14. Protons: positive charge in nucleus, number defines the type of element. Radiometric Age Dating http://education.jlab.org/qa/atom_model_03.gif 7 protons = Nitrogen

15. Radiometric Age Dating http://education.jlab.org/qa/atom_model_03.gif Nitrogen Atomic Number: number of protons. 7 protons = Nitrogen

16. Electrons: negative charge orbit nucleus, number commonly the same as protons (but may vary). Radiometric Age Dating http://education.jlab.org/qa/atom_model_03.gif

17. Neutrons: neutral charge in the nucleus, approximately the same number as protons (but varies). Radiometric Age Dating http://education.jlab.org/qa/atom_model_03.gif

18. Atomic Mass: Number of Protons + Number of Neutrons Radiometric Age Dating http://education.jlab.org/qa/atom_model_03.gif 7 Protons + 7 Neutrons = Atomic Mass of 14 Nitrogen

19. Radiometric Age Dating 8 Protons + 8 Neutrons = Atomic Mass of 16 http://www.biologycorner.com/resources/oxygen.gif Atomic Mass: Number of Protons + Number of Neutrons Oxygen

20. Radiometric Age Dating 6 Protons + 6 Neutrons = Atomic Mass of 12 Atomic Mass: Number of Protons + Number of Neutrons Carbon + + + + + + N N N N N N Carbon 12

21. Radiometric Age Dating Isotope: Atom with unequal number of Protons and Neutrons Carbon + + + + + + N N N N N N N

22. Radiometric Age Dating Isotope: Many isotopes are "stable". (they do not change with time). Carbon + + + + + + N N N N N N N

23. Radiometric Age Dating 6 Protons + 7 Neutrons = Atomic Mass of 13 Atomic Mass: Number of Protons + Number of Neutrons Carbon + + + + + + N N N N N N N Carbon 13 Stable Isotope

24. Radiometric Age Dating Isotope: Some isotopes are ”unstable". (they spontaneously change to a more stable state through radioactive decay). Carbon + + + + + + N N N N N N N N

25. Radiometric Age Dating 6 Protons + 8 Neutrons = Atomic Mass of 14 Atomic Mass: Number of Protons + Number of Neutrons Carbon + + + + + + N N N N N N N Carbon 14 N Unstable Isotope

26. Radiometric Age Dating A number of ways in which decay can occur: sub-atomic shifts that give off small particles with energy http://athene.as.arizona.edu/~lclose/teaching/a202/radioactive-atom.gif

27. Radiometric Age Dating Radioactive Decay: some kinds with minor energy some with lethal energy some one step to stable some multiple

28. Radiometric Age Dating Uranium 238 Lead 206 Many steps, each with energy

29. Radiometric Age Dating Radioactive Decay: rate is constant (for an isotope) decay is spontaneous & random

30. Radiometric Age Dating Half Life: the time it takes for 1/2 of the unstable parent atoms to decay to the stable daughter form.

34. 0.5 half-life

35. Radiometric Age Dating Obtaining Radiometric Dates: as minerals crystallize they incorporate atoms of some radioactive isotopes.

36. Radiometric Age Dating http://www.sgs.org.sa/Content/images/zircon.jpg http://uts.cc.utexas.edu/~rmr/images/Indiansun.GIF zircon Granite trace amounts Uranium 238

37. Radiometric Age Dating Obtaining Radiometric Dates: unstable isotopes decay at a constant rate.

38. Radiometric Age Dating Obtaining Radiometric Dates: as % of parent decrease, % of daughter increases Total remains the same (100%)

39. Radiometric Age Dating Obtaining Radiometric Dates: Measure the ratio of Parent : Daughter (not absolute count of atoms)

40. Radiometric Age Dating Mass Spectrometer: instrument to measure isotopic ratios

41. Radiometric Age Dating Calculating age: 1. Convert % of parent remaining to the number of 1/2 lives this represents. 100% 0 - half life 50% 1 - half life 25% 2 - half life 12.5% 3 - half life Parent

42. Radiometric Age Dating Calculating age: 2. Multiple the number of 1/2 lives by the time it takes for one half of the isotope to decay

43. Radiometric Age Dating Calculating age: Half Life Carbon 14 = 5,730 yrs Potassium 40 = 1,300,000 yrs Uranium 238 = 4,500,000,000 yrs

44. Radiometric Age Dating Calculating age: example 12.5% parent = 3 half lives

45. Radiometric Age Dating Calculating age: example (one half life for Uranium = 4.5 billion yrs) Age = 3.0 half-lives x 4.5 billion yrs Age = 13.5 billion years billion yrs

46. Radiometric Age Dating Calculating age: example This dates the time that the mineral grain formed. http://earth.boisestate.edu/home/markschmitz/schmitz_research.html

47. Radiometric Age Dating Calculating age: If rock is made out of pieces of other rocks (sediment)... date is the parent rock.

48. Radiometric Age Dating Calculating age: Therefore igneous rocks are most often used for radiometric dating. rhyolite - andesite - basalt granite - diorite - gabbro

49. Radiometric Age Dating Calculating age: Love the bentonite = volcanic ash bed. http://www.gns.cri.nz/inquatephra/

50. Radiometric Age Dating Calculating age: http://www.csc.edu/geoscience/toadstool/images/datadisttoash.jpg Love the bentonite = volcanic ash bed.

51. Radiometric Age Dating Sedimentary rocks are often dated by: (1) bounding with igneous rock dates and (2) correlation with fossils

52. Radiometric Age Dating

53. Assumptions: range of half-life must be appropriate - short enough for measurable decay - long enough for parent to still be present

54. Radiometric Age Dating Assumptions: range of half-life must be appropriate Uranium - Lead igneous rocks greater than 100 million years

55. Radiometric Age Dating Assumptions: range of half-life must be appropriate Potassium - Argon igneous rocks greater than 100,000 years

56. Radiometric Age Dating Assumptions: range of half-life must be appropriate Carbon 14 organic material less than 80,000 years

57. Radiometric Age Dating Assumptions: must be a closed system no parents added or removed no daughters added or removed

58. Radiometric Age Dating Assumptions: must be a closed system metamorphism: "opens" the system and resets the clock modern weathering: "opens" the system

59. Radiometric Age Dating How Accurate?: Very first date: Cambrian - Precambrian ~ 600,000,000 yrs

60. Radiometric Age Dating How Accurate? Acceptable error: current standard (+ or – 1.0%)

61. Radiometric Age Dating How Accurate? Acceptable error: 500,000,000 x 0.01 + or – 5 million yrs

62. Radiometric Age Dating How Accurate? Knowledge of your own weight? 1.________ actually ________ difference ________ as % ________

63. Radiometric Age Dating Fission Tracks:

64. Radiometric Age Dating Lake varves: seasonal deposits of mud in lakes very accurate record up to 100,000 yrs.

65. Radiometric Age Dating Tree-rings: annual rings climate affects the width patterns can be correlated regionally 8000 yr. record

66. Radiometric Age Dating Ice cores: annual accumulation of snow on glaciers ~100,000 year record