PowerPoint PresentationSlide 2Slide 3Slide 4the key to the pastrelative time and relative orderrelative age dating conceptsSlide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27Slide 28Slide 29Slide 30Slide 31Slide 32relative age: correlationSlide 34Slide 35Slide 36Slide 37Slide 38Slide 39Slide 40Slide 41Slide 42Slide 43age of the EarthSlide 45Slide 46Slide 47Slide 48Slide 49Slide 50Slide 51Slide 52basic geochronological assumptionsInstruments and TechniquesClean Lab - Chemical PreparationThermal Ionization Mass SpectrometerSchematic of Sector MSZircon Laser Ablation PitRate Law for Radioactive DecayRb/Sr Age Dating EquationRb/Sr Isochron SystematicsIndependent Checks on Radiometric AgesOther dating methods: dendrochronologyrelative and absolute dates combinedgeological time scaleSlide 66Slide 67Slide 68geologic timetime is critical for geologic processesRockies and Alps are ~3000 m tallAtlantic Ocean is ~5000 km acrossfor comparison: fingernail grows at 1 cm/yr-- mountains grow at ~1 meter per 5000 yrs (0.2 mm/yr)-- 3000 m x 5000 yr/m = 15,000,000 (yrs necessary)-- today, seafloor spreading in Atlantic is ~4 cm/yr-- 6000 km = 6000 km x 1000 m/km x 100 cm/m = 600,000,000 cm-- 600,000,000 cm / 4 cm/yr = 150,000,000 yearsage of the Earthprior to 19th century, accepted age from religious beliefs-- 6,000 years for Western culture (Christian)…Bishop Usher from geneology in the Bible-- old beyond comprehension (Hindu/Buddhist/Chinese)during 19th century, length of time required forgeologic processes to occur was recognized-- age not certain (Islam)-- fundamental contribution of geology to scientific knowledgeJames Hutton (1726-1797) “Father of Modern Geology” •native of Edinburgh, Scotland •educated as a medical doctor in Leiden (1749) •passionate about scientific inquiry historical developments“Theory of the Earth” -- processes are slow; take a long timeCharles Lyell (1795-1875)•Scotsman who attended Oxford University •father was an avid naturalist •rebelled against prevailing thought of “catastrophism”. “Principles of Geology” -- popularized Hutton’s viewsidea of “uniformitarianism” -- same processes operating today occurred in the past….the present is the key to the past….the key to the paststudy of timing of geologic events and processes is geochronologyrelative time vs. absolute timerelative timeorder of events or objects from first (oldest) to last (youngest)she is older than he is; she was born first and he was born last age of events or objects expressed numericallyshe is twenty-one and he is nineteen absolute timerelative time and relative orderapply simple concepts to determine…• original horizontality• superposition• lateral continuity• cross-cutting relationships• inclusions• unconformitiesrelative age dating conceptsoriginal horizontalityall beds originally deposited in water formed in horizontal layerssediments will settleto bottomand blanketthe sea floorrelative age dating conceptssuperpositionwithin a sequence of undisturbed sedimentary or volcanic rocks,oldest rocks are at the bottom and youngest at the top….young upward…oldestyoungestlateral continuityoriginal sedimentary layers extend laterally until they thin at edgescontinuecontinuerelative age dating conceptscross-cutting relationshipsa disrupted pattern is older thanthe cause of the disruptione.g. an intrusion is youngerthan the rocks it intrudesrelative age dating conceptsinclusionsfragments of other rocks contained in a body of rockmust be older than the host rocke.g. 1) xenoliths in granite are olderthan granite and2) pieces of rock inconglomerate are older than conglomerateQuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.relative age dating conceptsunconformitiesa contact between sedimentary formations that represents a gap in the geologic record -- “gap” represented is variable (i.e. amount of time or the amount of missing section)different types of unconformitiesconformity• relatively continuous deposition• deposition of a sequence of parallel layers• contacts between formations do not represent significant amounts of timefrom: http://www.elohi.com/photo/grandcanyonconformityrelative age dating conceptsdifferent types of unconformitiesangular unconformity• contact separates overlying younger layers from tilted older layers• sequence of layers is not parallel• contacts between formations may represent significant amounts of timeangular unconformityangular unconformityfrom: http://www.uakron.edu/envstudies/parks/rmgcan2.htmlangular unconformityrelative age dating conceptsdifferent types of unconformitiesdisconformity• contact separates beds (formations) that are parallel• sequence of layers is parallel• contacts between formations may represent significant amounts of time• missing time is difficult to recognize (may need otherinformation--paleosol?)relative age dating conceptsdifferent types of unconformitiesnonconformity• strata deposited on older crystalline (metamorphic/igneous) rock• erosion surface on igneous/metamorphic rock covered bysedimentary rocks• large gap in geologic recordnonconformitywhat events occur?angular unconformitywhat events occur?nonconformitynow that we know all this…what happened?depositionintrusiontilting and erosionsubsidenceand reneweddepositionmissing formation (time)?dike intrusionerosion and exposuresubsidence and depositionuplift/sea level fall and river depositionrelative ages of the formationscorrelation -- determining time equivalency of rocks within a region, between continents, etc.physical continuityrelative age: correlationphysically following a continuous exposure of a rock unit--most direct; easily done in some locations, not in otherse.g. within the Grand Canyonhow is this done?lithologic similarityassuming similar sequences of rocks formed at same time-- inaccurate if common rocks are involvede.g. the Grand Canyon and Zion National ParksCoconino Sandstonephysical continuity -- Coconino Sandstone in Grand Canyonlithologic similarity -- Coconino and Navajo Sandstoneslithologic similarity -- Coconino and Navajo SandstonesNavajo is much younger!faunal succession (correlation by fossils)relative age: correlationhow is this done?index fossil short-lived organism; points to narrow range of geologic timefossil species succeed one another