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Absolute Dating. 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.

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Presentation on theme: "Absolute Dating. 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."— Presentation transcript:

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 Humans 11:20 pm

3 1 second 1/ 31,556, of the year ,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 U Th He ( 2protons + 2 Neutrons) Alpha Decay Beta Decay Th Pa + e- Neutron splits into a proton and an electron

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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 /61 6/6 Half-lifes 012 grams / 0 grams 2 3/92 3/ /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 / nd 256 / rd 128 / th 64 / ,00020,00030,00040,000

18 Parent/DaughterHalf Life (yrs)Range (yrs) 238 U/ 206 Pb 14 C 3 H/ 3 He 4.5 billion 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

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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?


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