1. Absolute Dating

2. J F M A M J J A S O N D J Earth Forms Earth Cools First Life Abundant Oxygen Multicellular Organisms Plants and Animals Dinos 15-25 Humans 11:20 pm

3. 1 second 1/ 31,556,925.974 of the year 1900 9,192,631,770 flips of the magnetic field of a cesium atom

4. What is Absolute/Numerical Dating? The age of an earth material or event in years Relative age 1 st 2 nd 3 rd Absolute 1.7 bya 95 mya 12 kya youngest 8 kya

5. Estimating Earth's Age - Early (failed) Attempt Bishop Usher – Biblical Interpretation 4004 BC – before the birth of Christ October 21 9:00 in the morning

6. Estimating Earth's Age - Early (failed) Attempt Sedimentation rates - 3 my – 500 my Halley/Joly - Ocean Salinity – 100 my Lord Kelvin – Rate of Cooling – 30 my

7. Radioactive Revolution around 1900 Radioactive decay - spontaneous transformation of an element to another isotope of the same element or another element.

8. Pieces of an Element Protons - positively charged Neutrons - no charge Electrons - negatively charged N e P P e

9. Isotope - element with different number of neutrons in the nucleus. P e N P N e Hydrogen - stableTritium - unstable

10. Radioactive Decay N P N e Tritium N P P e e Helium 3 unstablestable nuclear decay (daughter) (parent)

11. Alpha Decay – loss of a positively charged He ion Beta Decay – neutron splits into proton and electron Radioactive Decay

12. 238 92 U 234 90 Th + 4242 He ( 2protons + 2 Neutrons) Alpha Decay Beta Decay 234 90 Th 234 91 Pa + e- Neutron splits into a proton and an electron

14. Half-life The fixed period of time during which half the parent atoms present in a closed system decay to form daughter atoms

15. Half-Life 12354

16. Half-life Potassium 40 / Argon 40 1 6/61 6/6 Half-lifes 012 grams / 0 grams 2 3/92 3/9 3 1.5/10.5

17. Half-Life Exercise Isotope AIsotope B Parent Daughter Sample: 1024 grams 64 grams 960 grams (10 k) half-life 1 st 512 / 512 2 nd 256 / 768 3 rd 128 / 896 4 th 64 / 960 10,00020,00030,00040,000

18. Parent/DaughterHalf Life (yrs)Range (yrs) 238 U/ 206 Pb 14 C 3 H/ 3 He 4.5 billion 5730 12.3 10 million to 4.5 billion 100 to 70,000 1 to 50

19. Parent/Daughter 238 U/ 206 Pb 14 C 3 H/ 3 He Material Dated Igneous and Metamorphic rocks Organic material Water

20. Uranium (U) - Thorium (Th) - Lead (Pb) 238U decays to 206Pb (4.5 billion) 235U decays to 207Pb (713 million) 232Th decays to 208Pb (14.1 billion) >Rocks containing Uranium provide three possible techniques. >Because all three occur together, it allows a method to cross-check the dates. >Uses zircons, uraninite and uranium ores

21. Potassium (K) - Argon (Ar) Dating >Potassium (K) is an extremely common element. >Half-life (t1/2) is 1.3 billion years. >Range is 100,000 to 4.6 billion years. >Useful for relatively young and very old rocks. >Found in muscovite, biotite, orthoclase and glauconite. >Used to date volcanic rocks.

22. Carbon 14 / Carbon 12 >Cosmic rays hit Nitrogen 14 changing it to Carbon 14. >Carbon 14 is taken in by organisms. >When organism dies, amount of C-14 decreases.

23. Magnetic Polarity Dating

26. Dating techniques that can be used on this geologic column: absolute dating paleomagnetism superposition fossil correlation

27. What is the Parent / Daughter ratio of a sample of radiogenic material if the original sample was 200g. and 3 half-lifes have passed. If the half-life is 20,000 years, how old is the sample? What is the half-life of an isotopic pair if the sample is 2 million years old and contains 625g of parent and 9375g of daughter isotope?