Lecture 6 – Geological Time and Fossil RecordI filed a tax return this tax seasonMeasuring Time in MacroevolutionProblems with using only Phylogeny of living organismsProblems with using only the fossil recordTodayI. Fossil FormationFossils are preserved remains of past living organismsFossils are Preserved in Sedimentary RocksSedimentary Rock FormationModes of FossilizationImpression FossilPermineralized FossilsSlide 14Casts and MoldsTrace FossilsPowerPoint PresentationUnaltered remainsUnaltered RemainsSlide 20Slide 21Fossils: Biased RecordII. Geological Time How do we know how old a fossil is?Geological Time is divided into a series of eons, eras, periods, and epochsGeological ages were first described by characteristic fossil faunas Now understood through relative and absolute dating techniquesRelative Versus Absolute AgeSlide 27Principles in Geological DatingLaws of Stratigraphy 1Slide 30Laws of Stratigraphy 3Laws of Stratigraphy 4“Index Fossils”Unconformities Can OccurPolystrate fossilsRelative datingIgneous Rocks Can Be Dated Directly, NOT SedimentaryAbsolute Geological time is inferred by radioactive dating techniquesRadioactive Decay is Exponentially ConstantUnique rates of decaySlide 41Slide 42Slide 43Slide 44Slide 45III. Major Features of the Fossil Record and History of Life on EarthEarth Has Changed Over Time: Continental DriftEarth Has Changed Over Time: Climate ChangeEarth Has Changed Over Time: Oxygen ContentOrigin of LifeArchean 3.8-2.5 Billion YearsOldest Fossils - StromatolitesModern Stromatolites in W AustraliaEvolutionary Events of the ProterozoicOrigin of Multi-cellular OrganismsDickensonia from VendianPteridinium may be extinct phylum may be similar to cnidariaNemiana Anemone? But no tentacles Protist? Algae? Extinct Phylum?Paleozoic EventsCambrian ExplosionBurgess Shale Fossils: OpabiniaBurgess Shale Fossils: PikaiaBurgess Shale Fossils: AnomalocarisSlide 64Chengjiang FaunaColonization of LandRecently discovered Devonian “Missing Link”Slide 68The Crew (2004)End-Permian Extinction Marks the End of the PaleozoicMesozoic EraMesozoic: Angiosperm OriginsK/T BoundaryCenozoicGeological Eras of PhanerozoicAnti-evolutionist arguments and fossil recordSlide 77Slide 78Slide 79ExampleLecture 6 – Geological Time and Fossil RecordI filed a tax return this tax season•TRUE•FALSEm.socrative.com room: eemb102Measuring Time in Macroevolution•Phylogeny•Fossil Record•Both are inadequate alone – a combination is bestProblems with using only Phylogeny of living organisms•No true temporal component•All species are living now•All inferences about true time must come from our assumptions about change with timeProblems with using only the fossil record•Timing of fossil is meaningless if we don’t know its relationships•Must know species or higher taxonomic level to which it belongs (requires phylogeny)Today•Fossil Formation•Geological Time•Overview of the fossil recordI. Fossil FormationFossils are preserved remains of past living organismsHow do organisms fossilize?Fossils are Preserved in Sedimentary Rocks•Igneous Rocks – Solidified molten rock material. Formed by volcanic action.•Sedimentary Rocks – Formed by sedimentation of small rock particles•Metamorphic Rocks – Sedimentary or Igneous rocks changed by pressure and time changeSedimentary Rock FormationForm from pre-existing rock particles - igneous, metamorphic or sedimentary. The Parent rock undergoes WEATHERINGchemical and/or physical mechanisms break rock into smaller particles. Particles are TRANSPORTED by ice, air or water to a region of lower energy called a sedimentary basin. Turned to rock by:COMPACTION (decrease in rock volume due to weight of overlying sediment) CEMENTATION (chemical precipitation in pore spaces between grains which "glues" the rock together.Modes of Fossilization•Compression/Impression Fossils–When organic material is buried in sediment before decomposing–Weight from above causes impression below–Like a hand print in cement–Finer sediments record more detail–More common in plants (minimal distortion)Impression FossilGingko LeafPermineralized Fossils•Structures are buried in sediments•Dissolved minerals precipitate in the cells•Can preserve details of internal structurePermineralized FossilsT. rexPetrified WoodCasts and Molds•When remains decay after burial in sediment•Molds are unfilled spaces. Casts are filled moldsOligocene pine coneTrace Fossils•(fossilized nests, burrows, footprints, etc.)Dinosaur FootprintTrace FossilsTrilobite TracesTrail showing the central paired leg grooves and the parallel furrows on the outside edges. The curved shape suggests a searching patternTracks are attributed to Isotelus trilobites walking on the surface, rather than plowing (furrowing) through the surface layersUnaltered remains•Preserved in environments that prevent decay•Acid, permafrost, arid, amber•Quite rareUnaltered Remains Insect in AmberAncient DNAUnaltered Remains Mammoth preserved in permafrost (40,000 years)Unaltered Remains 2400 year old remains of human from acidic peat bog(C14 radiocarbon dated)Fossils: Biased Record•Some groups far more likely to fossilize•Hard mineralized parts (bones, shells, teeth)•Burial required–Favors benthic (bottom-dwellers)•Marine species more common fossils (ocean sediments)•Older rocks (and therefore fossils) are rarer because of erosion and subductionII. Geological TimeHow do we know how old a fossil is?Geological Time is divided into a series of eons, eras, periods, and epochsGeological ages were first described by characteristic fossil faunasNow understood through relative and absolute dating techniquesRelative Versus Absolute Age•Relative Age - we can determine if something is younger, older, or as old as something else. We can infer sequences of events, but not exact age.Relative Versus Absolute Age•Absolute Age - We can assign a number (in units of time) to the amount of time that has passed.18351875Principles in Geological Dating•Laws of Stratigraphy•Relative dating and correlation•Absolute dating - estimated by radioactive decayLaws of Stratigraphy 1•Original Horizontality – strata laid down parallel to Earth’s surfaceLaws of Stratigraphy 2•Lateral continuity– strata are generally continuous over large areasLaws of Stratigraphy 3•Superposition – Older strata are lower•Faunal succession- Fossil groups are succeeded by other fossil groups