2Radioactive IsotopesScientists can determine the numerical age of rocks and other rocksExamining radioactive isotopesExamining the remains of fossilsWhat is an isotope?
3Radioactive Isotopes Radioactive decay Definition: the emission of radioactive particles and the resulting change into other isotopesDecay is constant so scientists can determine absolute age.Radioactive isotopes emit nuclear particles at a constant rateAs number of protons change, the original radioactive (parent) isotope is converted to a new element (daughter)Compare Absolute-Age dating to Relative-Age dating.
4Radiometric DatingAs parent atoms decrease during radioactive decay, the number of daughter atoms increaseRatio of parent to daughter atoms indicate how much time has passedWhat percent of daughter isotopes would exist in a sample containing 50 percent parent isotope?
5Half-LifeThe length of time it takes for one-half of the original isotope to decayAfter 1 half-life 50% of the parent remains (1:1 ratio with daughter)After 2 half lives, one half of the remaining parent decays (25:75 ratio of the original parent to daughter)What would the ratio be for 3 half-lives?
6Dating RocksDating igneous or metamorphic rock requires the examination of parent-daughter ratios of minerals that make up the rock.Best isotope to use for dating depends on the appropriate age of rock being dated.Uranium 235 has a half life of 700 million yearsUsed for dating rocks 10s of million years old.The dating isotope must have a half life that is longer than the rock being tested.Explain why radiometric dating is not used for sedimentary rocks?
7Radiocarbon DatingCarbon-14 (C-14) is used to determine the age of organic materials.Plant and animal material: bones, charcoal, amberC-14 has a shorter half-life than other isotopes.Living organisms replenish C-14 when aliveAt death the C-14 begins to decreaseMeasuring the amount of C-14 in a sample indicates how much time has passed since its deathUsed for dating recent geological events.Why is radiocarbon dating used for recent geological events?Compare and contrast the use of U-238 and C-14 in absolute age dating.
8Other Ways to Determine Absolute Age Tree RingsAnnual rings in trees consist of two seasonal ringsEarly and late seasonRings show conditionsTrees in same geographical region have similar ring patternsDendrochronology: the science of using tree rings to determine absolute aging.Describe how archaeologists use dendrochronology to calculate the age of finds?
9Other Ways to Determine Absolute Age Ice CoresContain a record of past environmental conditionals in annual layers of snow.Summer ice has more bubbles/larger crystalsStudy glacial cyclesHow could ice cores be used to study climate change? Give exmples.
10Other Ways to Determine Absolute Age VarvesBands of alternating light and dark colored sediments of sand, clay and siltRepresent the seasonal deposition of sedimentsLakesSummer deposits: Sand sized particles with traces of living matterWinter deposits: Thin fine grained sedimentsDescribe the usefulness of Varves to geologists who study glacial lake deposits.
11Vocabulary Absolute-age dating Radioactive decay Radiometric dating Half lifeRadiocarbon datingDendrochronologyVarveIsotope