Geologic TimeGeologic timePowerPoint PresentationSlide 4Relative time The order in which events occurSlide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Uplift and exposure or Non-deposition of sedimentSlide 23Slide 24Slide 25Slide 26Slide 27Slide 28Slide 29Slide 30Slide 31Slide 32Slide 33Slide 34Slide 35Slide 36Slide 37Absolute AgesSlide 39Slide 40Slide 41What to know from thisGeologic TimeLecture 16Geologic time•How do we separated events in the geologic past?•How was the geologic time scale created?•How do we calculate and apply Absolute time?•How old is earth?-4.6 Billion years oldGEOLOGIC TIME“Time” sets geology apart from other natural sciencesAll cultures, all societies, all religions are interested in geologic time, and all have explanations for: How the Earth originated Where THEY came fromComprehending geologic time1871 1968Relative timeThe order in which events occur•Stratigraphic principles–Original Horizontality–Superposition–Cross-cutting relationships–Law of Faunal Succession12345Steno’s Law of Original Horizontality: layers of sedimentary rock are always deposited in a nearly horizontal planeSteno’s Law of Original Horizontality: layers of sedimentary rock are always deposited in a nearly horizontal planeSteno’s Law of Superposition: in any sequence of sedimentary rocks, the oldest beds are at the bottom and the youngest are at the topOlderYoungerPrinciple of SuperpositionGrand Canyon, ArizonayoungoldApplication of the Laws of Horizontality and SuperpositionMountain Building: a History of EventsPrinciple of Original Horizontalitytilted beds (tilting occurs after deposition)horizontal bedsJames Hutton (1795)Principle of Cross-Cutting Relationships: a pattern that is disrupted is older than whatever caused the disruptionblackgraywhitePrinciple of Cross-cutting Relationshipsigneous intrusionfaultWilliam Smith (1815)Law of Faunal Succession: Fossil organisms succeed each other in time in an orderly and recognizable mannerApplication of the Law of Faunal SuccessionQuarryCanalHillApplication of the Law of Faunal SuccessionQuarryCanalHillApplication of the Law of Faunal SuccessionQuarryCanalHillApplication of the Law of Faunal SuccessionQuarryCanalHillApplication of the Law of Faunal SuccessionQuarryCanalHillCorrelation Across Large DistancesINDEX FOSSILSJames Hutton (1795)“I see no vestige of a beginning, no prospect of an end”“The present is the key to the past”Deposition (1)deposition (2)erosion12erosiontiltingPrinciple of Uniformitarianism: the processes that shaped the Earth throughout its history were the same processes as those operating todayUplift and exposure or Non-deposition of sediment•A “gap” in Geologic record•Unconformities–Angular unconformity–Disconformity–Non-ConformityUnconformities: Gaps In the Rock RecordANGULAR UNCONFORMITYHorizontal beds overlie a flat erosional surface formed from titled or folded bedsUnconformities: Gaps In the Rock RecordANGULAR UNCONFORMITYUnconformities: Gaps In the Rock RecordNONCONFORMITYSedimentary rocks overlie igneous or metamorphic rocksSed.Ign.Unconformities: Gaps In the Rock RecordDISCONFORMITYSedimentary rock overlie parallel sedimentary beds (need an erosional surface or absolute dates to identify)Sedimentation Rates Not Always ConstantDevelopment of the Geologic Time Scale12384567unconformity(an interval of geologic time that is NOT represented by the rock record)Development of the Geologic Time ScalePrecambrianPhanerozoicSimple algae and fungiComplex invertebrates, vertebrates, and plantsinvertebrates vertebrates plantsDevelopment of the Geologic Time ScalePaleozoic(ancient life)PrecambrianPhanerozoicinvertebrates vertebrates plantsDevelopment of the Geologic Time ScaleMesozoic(middle life)PrecambrianPaleozoic(ancient life)Phanerozoicinvertebrates vertebrates plantsDevelopment of the Geologic Time ScaleCenozoic(recent life)PrecambrianMesozoic(middle life)Paleozoic(ancient life)Phanerozoicinvertebrates vertebrates plantsPaleozoic MesozoicPrecambrianCambrianOrdovicianSilurianDevonianCarboniferousPermianTriassicJurassicCretaceousPaleogeneNeogeneEarliest fossilsOxygen enters the atmosphereEvolutionary explosionFirst fish1st generation of Appalachian MountainsFirst land plantsFirst amphibians2nd generation of Appalachian MountainsExtensive coal-forming swamps3rd generation of Appalachian Mountains95% of all species become extintDinosaurs evolveEarly mammals evolveFlowering plants evolveExtinction of the dinosaursEarliest primatesIce Age beginsFirst Homo sapiensDevelopment of the Geologic Time ScaleCenozoic***Absolute time scaleBased on the fact that the isotopes of some elements undergo radioactive decayRadioactive Decay% percent of sample as parent or daughter100%50%25%12.5%1 2 3 4 5time (half-lives)K/Ar 1.3 2.6 3.9 5.2 6.5billion yrs (by)Determining the age of a sampleThe rate of decay is constant for a given radioisotope, so if you can determine the amount of parent material and the amount of daughter material, you can estimate the age of the sampleAbsolute Ages•The isotopes form in Igneous or Metamorphic rocks (crystalline rocks)•Record the Age the Rock was either:–Cooled (formed)–MetamorphosedWhen used in conjunction with stratigraphic principles, age estimates for other rock types can be made4,600 million years570 million years248 million years65 million years You are here!What to know from this•Relative time v Absolute time•Stratigraphic principles•Unconformities•Radioactive decay dating•Absolute Ages of:–Earth, Paleozoic, Mesozoic,