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Radiometric dating / Sediment accumulation I Principles II Assumptions III 14 C Production rate Reservoir corrections Circulation effect Deep-water age IV 230 Th - 234 U Decay vs. production Constant accumulation model Constant 230 Th flux model 230 Th V Other… Radiometric (Ar-Ar) Annual (varves) Cyclical (orbital)

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Dating sediment goal Establish age-depth relationship

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Terminology Parent Daughter Isotopes Stable Radioactive alpha, beta, gamma decay

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Radioactive decay Spontaneous emission Nuclear transformation Loss of parent Growth of daughter

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Definitions Decay constant Activity Half life Mean life

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Application Balance of Resolution vs. longevity 14 C useful for last climate cycle.

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Reporting convention Time zero = 1950 Half life = 5730 y del notation vs. stand.

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Definitions Decay constant Activity Half life Mean life

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Age and accumulation Assumptions Uncertainty

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Dating sediment goal Establish age-depth relationship

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Bioturbation Sediment imperfect recorder Bioturbation example of filter

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Reservoir effect Transfer from one reservoir to another takes time.

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Variable pathways Sources Sinks

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Different scales Radiocarbon and calendar

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Solar variabiluty Sunspot cycles and 14 C production

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Age offsets Long-term trend

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Age offsets Ocean and climate Influences possible.

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Hughen et al. Comparisons Independent chronologies allow test of influences.

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Age offsets

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Evolving production Atmospheric 14 C and magnetic field inverse.

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14 C through time Complications of Carbon cycle, physical and chemical cycling.

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Ocean circulation Influence on apparent age

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Age plateaus

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Age anomalies Modeling ocean and production variations.

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Uranium series Absolute chronology?

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Parent decay to stable daughter

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Secular equilibrium Between long half- life parent and shorter half-live daughter

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Uranium series Different approaches 1.Corals 2.Deep-sea sediments

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Uranium series Downcore approach

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Uranium series Assume constant deposition, estimate rate.

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Uranium series Second approach. Assume constant flux of decay product, estimate instantaneous rates of sedimentation.

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Uranium series Reasonable assumption

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Uranium series Integrated approach (Sacketts method).

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Uranium series Test of (Sacketts method).

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Uranium series Test of Sacketts method.

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Uranium series Works for special case.

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Extraterrestrial IDPs New 3He approach.

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Ar - Ar method Dating tool for longer time, lower resolution.

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Earth Science Chapter 21 Section 3

Earth Science Chapter 21 Section 3

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