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GEOG 205 (26)
Lecture

DatingMethods.pdf

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Department
Geography
Course
GEOG 205
Professor
Paquinand Heumann
Semester
Winter

Description
Dating Methods precision vs accuracy - will be on exam, know how to distinguish examples Precision - Refers to a statistical uncertainty that relates to a physical or chemical measurement, it also refers to the ability of the measurement to be repeated under the same conditions - if I get my mark here, can I get it here again? Accuracy - Refers to the degree of correspondence between the age and the dating technique - that means, how close does the dating technique actually come to the true age of the item being dated? Radiometric Methods Based on radioactive decay of certain unstable chemical elements or isotopes Carbon-14 Potassium-40 to Argo-40 Uranium-238 to lead-206 see slide for age rage dated Carbon-14 up to 40,000 years ago Carbon-14 Carbon 14 dating is a policeable to all organic material back up to 40,000 years ago c-12 and c-13 are stable isotopes c-14 is a radioactive isotope As long as the being is living, C-14 is constantly being replenished Decay begins at death c-14 has a half life of 5730 +- 40 years carbon 14 production varies depending on solar activity - during increased sun spots there's less c14 and vice versa isotopic fractionation --changes (natural) in the ratio between carbon 14 and carbon 12 --adjust for changes in production and changes in fractionation (ratio between the two) circulation of marine carbon --the mixing rate between surface and deep ocean water is slow, so C14 in the deep ocean decays without being replenished contamination of organic sediments --younger/older carbon can be added to sample materials - bioturbation can cause mixing of soil, in wash of sediments as well from streams etc Incremental Dating Methods based on the regular accumulation of materials to organic tissues or sedimentary sequences Dendrochronology tree ring dating measures the increments of wood that are added annually to the perimeter of the tree ring width is a reflection of climate - the larger = favorable, smaller = less favorable problems with it: -standardization -missing or partial rings ---caused by extreme events -complacent and sensitive rings ---caused by slope, water retention capacity of the soil, the amount of shade the tree gets, genetic characteristics -false rings --occurs in times of extreme climatic events but this event is different because it can cause another ring to appear almost - ex/ summer comes to an end but the fall is mild, i.e. indian summer Lichenometry lichen are complex organisms in which fungi and algae live togethers - the algae provides carbs through photosynthesis and the fungi provides a safe environment for the algae to live this technique dates newly exposed surfaces using variations in lic
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