historical geology lecture 6 absolute time and dating geochronology
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Historical Geology
Lecture 6
Absolute Time and Dating
Geochronology
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Historical Geology
I Early Dating AttemptsII Isotopic Dating
A) Radioactive Decay1) Isotopes2) Types of Decay3) Half-life4) Decay Series5) Uses
B) Fission Track DatingC) Effect of Metamorphism
III Combining Relative and Absolute Dating
Outline
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Historical GeologyEstimating Earth’s Age
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Historical GeologyEstimating Earth’s Age
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Historical GeologyEarly Dating Attempts
QuantitativeWilliam Thomson, Lord Kelvin (1824-1907)method: cooling rate of molten Earth through conduction and radiationresult: 24-40 million years
John Joly (1857-1933)method: rate of delivery of salt to the oceanresult: 90-100 million years
Total salts in ocean / rate of addition = age
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Historical GeologyEarly Dating Attempts
Quantitative
Archibald Geikie (1835-1924); many othersmethod: sedimentation ratesresult: 3-1500 million years
Charles Lyell (1797-1895)method: evolution of marine mollusksresult: Cenozoic Era - 80 million years
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Historical GeologyThe Discovery of Radioactivity
Henri Becquerel (1852-1908)
Marie Curie (1867-1934)Pierre Curie (1859-1906)
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Historical GeologyIsotopes
isotopes - atoms of the same element that have different numbers of neutrons but the same number of protons
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Historical GeologyRadioactive Decay Types
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Historical GeologyHalf-Life
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Historical GeologyRadionuclides
Radioactive (parent)Radioactive (parent) Radiogenic (daughter)Radiogenic (daughter) Radioactive and RadiogenicRadioactive and Radiogenic CosmogenicCosmogenic
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Historical GeologyRadioactive Decay Systems
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Historical GeologyRadioactive Decay Systems
87Rb 87Sr
Half -life: 49 billion years
Effective Range: >10 million years
Source Materials: Potassium mica, Potassium feldspar, biotite, glauconite, whole metamorphic or igneous rock
Uses: Igneous rocksCarbonates - Sr composition of sea water
through timeMeteorites
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Half -life: 14 billion years
Effective Range: >10 million years
Source Materials: thorite, monazite, thorogummite, huttonite in granites and
basalts
Uses: stellar agessea floor nodules
Historical GeologyRadioactive Decay Systems
232Th 208Pb
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Historical GeologyRadioactive Decay Systems
238U 206Pb
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Half -life: 4.5 billion years
Effective Range: >10 million years
Source Materials: Zircon, uraninite, pitchblende
Uses: age of Earthmeteorites
Historical GeologyRadioactive Decay Systems
238U 206Pb
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Historical GeologyRadioactive Decay Systems
40K 40ArHalf -life: 1.25 billion years
Effective Range: >100,000 years
Source Materials: Muscovite, biotite, hornblende, volcanic rock, glauconite,
potassium feldspar
Uses: very old archaeological materials
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Half -life: 700 million years
Effective Range: >10 million years
Source Materials: zircon, urananite, monazite, apatite
Uses: dinosaur fossil dating
Historical GeologyRadioactive Decay Systems
235U 207Pb
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Half -life: 5,730 years
Effective Range: 100-40,000 years
Source Materials: Organic Matter
Uses: Radiocarbon Dating
Historical GeologyRadioactive Decay Systems
14C 14N
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Historical GeologyFission Track Dating
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Historical GeologyEffect of Metamorphism
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Historical GeologyUsing Absolute and Relative Dating
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Historical GeologyUsing Absolute and Relative Dating