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Radioisotopic/radiometric dating

Radioisotopic/radiometric dating

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Radioisotopic/radiometric dating

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  1. Radioisotopic/radiometric dating

  2. Radioisotopic/radiometric dating • Many believe in an old earth, i.e., billions of years old, due to radioisotopic dating

  3. Radioisotopic/radiometric dating • Many believe in an old earth, i.e., billions of years old, due to radioisotopic dating • But is this really the case? Is it true that the earth is billions of years old?

  4. Radioisotopic dating Some basic concepts

  5. Radioisotopic dating Some basic concepts Carbon 14 (14C)

  6. Radioisotopic dating Some basic concepts Carbon 14 (14C) 40K-40Ar

  7. Radioisotopic dating Some basic concepts Carbon 14 40K-40Ar Assumptions

  8. Radioisotopic dating Some basic concepts Carbon 14 40K-40Ar Assumptions Closing slides

  9. Data does not speak for itself.

  10. Data does not speak for itself. • Data must be interpreted within a philosophical framework.

  11. + + + + + + e- e- e- e- e- e- e- e- e- e- e- e-

  12. Three Types of Radioisotopic Decay

  13. Three Types of Radioisotopic Decay • Gamma radiation – photon of light emitted; atom does not lose mass

  14. Three Types of Radioisotopic Decay • Gamma radiation – photon of light emitted; atom does not lose mass • Alpha radiation – alpha particle has mass; when decay happens atom loses mass

  15. Three Types of Radioisotopic Decay • Gamma radiation – photon of light emitted; atom does not lose mass • Alpha radiation – alpha particle has mass; when decay happens atom loses mass • Beta radiation – loss of an electron; atom does not substantially lose mass

  16. Half-life • Parent – the original radioactive element

  17. Half-life • Parent – the original radioactive element • Daughter- the resulting element(s) from radioisotopic decay, or series of decay

  18. Half-life • Parent – the original radioactive element • Daughter- the resulting element(s) from radioisotopic decay, or series of decay • Half-life – the amount of time it takes for parent to decay to 50:50 parent/daughter ratio; e.g., 1,000,000 atoms of 238U would take 4.5 billion years to get 500,000 atoms each of 238U and 206Pb (one half-life); and second 4.5 billion yrs would result in 250,000 atoms of 238U and 750,000 atoms of 206Pb (two half-lives)

  19. Half-life • Parent – the original radioactive element • Daughter- the resulting element(s) from radioisotopic decay, or series of decay • Half-life – the amount of time it takes for parent to decay to 50:50 parent/daughter ratio; e.g., 1,000,000 atoms of 238U would take 4.5 billion years to get 500,000 atoms each of 238U and 206Pb (one half-life); and second 4.5 billion yrs would result in 250,000 atoms of 238U and 750,000 atoms of 206Pb (two half-lives) • At this time, unknown what causes an individual radioactive atom to decay while another does not

  20. Daughter 238U 238U 238U 238U 238U 238U 238U 238U 238U 238U 238U 238U 238U 238U 238U 238U 238U 238U 238U 238U 238U 238U 238U 238U 206Pb 206Pb 206Pb 206Pb 206Pb 206Pb 206Pb 206Pb ~4,500,000,000 years Parent Parent Half-life One half-life

  21. Daughter 238U 238U 238U 238U 238U 238U 238U 238U 238U 238U 238U 238U 238U 238U 238U 238U 238U 238U 238U 238U 206Pb 206Pb 206Pb 206Pb 206Pb 206Pb 206Pb 206Pb 206Pb 206Pb 206Pb 206Pb Half-life Two half-lives ~9,000,000,000 years Parent Parent

  22. Uranium 238 Decay Series α α α α α α α α β β β β β β 230Th 4.47 billion yrs 24 days 6.7 hrs 240,000 yrs 77,000 yrs 234Th 234U 234Pa 238U 1,602 yrs 3.8 days 3.1 min 27 min 20 min 206Pb 210Bi 214Po 210Pb 210Po 226Ra 218Po 222Rn 214Bi 214Pb 0.000164 sec 22 yrs 5 days 138 days stable

  23. Uranium 238 Decay Series α α α α α α α α β β β β β β 230Th 4.47 billion yrs 24 days 6.7 hrs 240,000 yrs 77,000 yrs 234Th 234U 234Pa 238U 1,602 yrs 3.8 days 3.1 min 27 min 20 min 206Pb 210Bi 214Po 210Pb 210Po 226Ra 218Po 222Rn 214Bi 214Pb 0.000164 sec 22 yrs 5 days 138 days stable

  24. Carbon 14 The late Willard F. Libby led team of scientists at University of Chicago during the post-II War period. 1949 first measured rate of 14C decay at 5568 ± 30years 1960 Libby received the Nobel Prize in Chemistry Half-life revised to 5730 ± 40 years (Cambridge half-life) 1950’s used Gas Proportional Counting to measure 14C Liquid Scintillation Counting (LSC) uses benzene, acetylene, ethanol, methanol, and other chemicals. Mid-1970’s development of Accelerated Mass Spectroscopy (AMS) The Atomic Mass Number is the sum of the number of protons and neutrons

  25. National Ocean Sciences AMS at Woods Hole Oceanographic Institution, Massachusetts. Photograph of Staff Physicist Robert Schneider placing a carousel of graphite targets into the ion source of the accelerator. Photo by Tom Kleindinst, 1995

  26. Air/atmosphere carbon molecules: 98.89% 12C 1.11%13C 0.0000000001% 14C, or 1 14C for every 1,000,000,000,000 12C

  27. Air/atmosphere carbon molecules: 98.89% 12C 1.11%13C 0.0000000001% 14C, or 1 14C for every 1,000,000,000,000 12C • 12C is stable

  28. Air/atmosphere carbon molecules: 98.89% 12C 1.11%13C 0.0000000001% 14C, or 1 14C for every 1,000,000,000,000 12C • 12C is stable • 13C is stable

  29. Air/atmosphere carbon molecules: 98.89% 12C 1.11%13C 0.0000000001% 14C, or 1 14C for every 1,000,000,000,000 12C • 12C is stable • 13C is stable • 14C is unstable; 14C changes back into 14N

  30. Air/atmosphere carbon molecules: 98.89% 12C 1.11%13C 0.0000000001% 14C, or 1 14C for every 1,000,000,000,000 12C • 12C is stable • 13C is stable • 14C is unstable; 14C changes back into 14N • Entire inventory of 14C is called the carbon exchange reservoir.

  31. Cosmic Rays Upper Atmosphere Atoms Neutrons Lower Atmosphere 14N 14N 14N 12C 12C + neutrons proton 14C CO2 CO2 14C 14C 12C 12C 12C 14C

  32. Cosmic Rays Upper Atmosphere Atoms Neutrons Lower Atmosphere 14N 14N 14N 12C 12C + neutrons proton 14C CO2 CO2 14C 14C 12C 12C 12C 14C

  33. Cosmic Rays Upper Atmosphere Atoms Neutrons Lower Atmosphere 14N 14N 14N 12C 12C + neutrons proton 14C CO2 CO2 14C 14C 12C 12C 12C 14C

  34. Cosmic Rays Upper Atmosphere Atoms Neutrons Lower Atmosphere 14N 14N 14N 12C 12C + neutrons proton 14C CO2 CO2 14C 14C 12C 12C 12C 14C

  35. Cosmic Rays Upper Atmosphere Atoms Neutrons Lower Atmosphere 14N 14N 14N 12C 12C + neutrons proton 14C CO2 CO2 14C 14C 12C 12C 12C 14C

  36. Cosmic Rays Upper Atmosphere Atoms Neutrons Lower Atmosphere 14N 14N 14N 12C 12C + neutrons proton 14C CO2 CO2 14C 14C 12C 12C 12C 14C

  37. Cosmic Rays Upper Atmosphere Atoms Neutrons Lower Atmosphere 14N 14N 14N 12C 12C + neutrons proton 14C CO2 CO2 14C 14C 12C 12C 12C 14C

  38. Cosmic Rays Upper Atmosphere Atoms Neutrons Lower Atmosphere 14N 14N 14N 12C 12C + neutrons proton 14C CO2 CO2 14C 14C 12C 12C 12C 14C

  39. Cosmic Rays Upper Atmosphere Atoms Neutrons Lower Atmosphere 14N 14N 14N 12C 12C + neutrons proton 14C CO2 CO2 14C 14C 12C 12C 12C 14C

  40. Known limitations • Size of sample is important. • the larger the better • purification and distillation removes some matter (LSC) • AMS better able to handle smaller samples • Requires great care in collecting and packaging. Carbon sample location requires careful stratigraphic examination. • Upper practical limit of 40,000 – 50,000 years, or 9 -10 half-lives. • Atmospheric 14C /12C ratio not always constant. • In general, single dates should not be trusted. Whenever possible multiple samples should be collected and dated from associated strata. (http://id-archserve.ucsb.edu/Anth3/Courseware/Chronology/08_Radiocarbon_Dating.html#C14Process)

  41. Other factors affecting 14C dating • Plants may discriminate against intake of 14C; plants are known to discriminate against 13C1 1. www.plantphys.net/article.php?ch=9&id=135

  42. Other factors affecting 14C dating • Plants may discriminate against intake of 14C; plants are known to discriminate against 13C1 • Reservoir effects 1. www.plantphys.net/article.php?ch=9&id=135

  43. Other factors affecting 14C dating • Plants may discriminate against intake of 14C; plants are known to discriminate against 13C1 • Reservoir effects • Suess or Industrial effect 1. www.plantphys.net/article.php?ch=9&id=135

  44. Other factors affecting 14C dating • Plants may discriminate against intake of 14C; plants are known to discriminate against 13C1 • Reservoir effects • Suess or Industrial effect • Atomic bomb effect 1. www.plantphys.net/article.php?ch=9&id=135

  45. Other factors affecting 14C dating • Plants may discriminate against intake of 14C; plants are known to discriminate against 13C1 • Reservoir effects • Suess or Industrial effect • Atomic bomb effect • Noah’s flood 1. www.plantphys.net/article.php?ch=9&id=135

  46. 14C in coal • C14 found in coal supposedly millions of years old

  47. 14C in fossils • C14 found in fossilized wood

  48. 14C in diamonds • Diamonds are believed to have formed 1-3 billion years ago • The earth’s mass is about 6x1027 g, which would be equivalent to about 4.3x1026 atoms of 14C • It takes 88 half-lives to get to a single atom of 14C • 88 half-lives is about 500,000 years.

  49. The presence of 14C in supposedly ancient coal, fossil wood, and diamonds falsifies the notion that the rocks or strata in which they were found are millions or years old.

  50. K-Ar dating