Absolute Age Dating

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Absolute Age Dating. Geological Time. Absolute time putting dates on geological events using radiometric dating and other techniques. Radiometric Dating Absolute dating using radioactive decay data. http://www.cotf.edu/ete/modules/msese/earthsysflr/geotime.html. Alpha Emission. - PowerPoint PPT Presentation

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Absolute Age Dating

Geological TimeAbsolute time putting dates on geological events using radiometric dating and other techniques.http://www.cotf.edu/ete/modules/msese/earthsysflr/geotime.html

Radiometric DatingAbsolute dating using radioactive decay data

Alpha EmissionBeta EmissionElectron Capture

Fig. 08.23Decay of 238UGeneral Decay RulesAtomic mass number No change DecreaseAtomic number Decrease Increase Alpha emissionBeta emissionhttp://www.asa3.org/ASA/resources/Wiens.html

Decay sequence for Uranium-238Half life the time it takes for half of the original element to decay to the new element.Half Life = 10,000 yrsDecays to DaughteriumStarting with 1,000,0000 nuclei of ParentiumHypothetical Element ParentiumTimeParentiumDaughterium1,000,00000500,000500,000+10,000250,000750,000+20,000TimeParentiumDaughterium125,000825,00062,500937,500+30,00031,250968,750+40,000+50,000ElapsedTimeParentiumDaughterium010,00020,00030,00040,00050,0001,000,000500,000250,000125,00062,50031,2500500,000750,000825,000937,500968,750010203040501,000,000250,000750,0000Time (thousands of years)NucleiParentiumDaughterium500,00040K238U235U87Rb40Ar206Pb207Pb87Sr1,250,000,0004,500,000,000713,000,00049,000,000,000100,000 - formation of Earth10,000,000 - formation of Earth10,000,000 - formation of Earth10,000,000 - formation of EarthParentDaughterHalf-life (yrs)Useful Range (yrs)Geologically Useful Radioactive Isotopes

Geologist collects samples of rockGeochemist finds radiometric ageGeologist interprets the geologic history of area during the time that the rock was being formed 40K238U235U87Rb40Ar206Pb207Pb87Sr1,250,000,0004,500,000,000713,000,00049,000,000,000100,000 - formation of Earth10,000,000 - formation of Earth10,000,000 - formation of Earth10,000,000 - formation of EarthParentDaughterHalf-life (yrs)Useful Range (yrs)Geologically Useful Radioactive IsotopesAn analysis of a feldspar crystal in a rock reveals that it contains 75% 40Ar and 25% 40K. How many half-lives have passed since the formation of the feldspar?Assuming the feldspar and rock formed at the same time, how old is the rock?238U235U206Pb207Pb4,500,000,000713,000,00010,000,000 - formation of Earth10,000,000 - formation of EarthParentDaughterHalf-life (yrs)Useful Range (yrs)An analysis of a zircon crystal in a rock reveals that it contains: 50.0% 238U and 50.0% 206Pb1.6% 235U and 98.4% 207Pb

How many half-lives of 238U have passed since the formation of the zircon?How many half-lives of 235U have passed since the formation of the zircon?What is the age of the zircon?