A typical rock formationRelative dating: some principles to follow...Wednesday, October 26, 11Principle of superpositionWednesday, October 26, 11Principle of original horizontalityWednesday, October 26, 11Principle of lateral continuityWednesday, October 26, 11Principle of cross-cutting relationshipsWednesday, October 26, 11Principle of inclusionsWednesday, October 26, 11Principles of unconformities (missing time)Wednesday, October 26, 11Radiometric Age Dating•Uses unstable isotopes of naturally occurring elements. The isotopes decay: they change into different elements or different isotopes of the same element.•The rate of decay is known (has been measured in the laboratory) for a variety of isotopes.•When igneous rocks form, there is 100% parent and 0% daughter isotopes in the rock.•The ratio of the parent and daughter isotopes can be measured using a mass spectrometer.Wednesday, October 26, 11Wednesday, October 26, 11MethodParent isotopeDaughter isotopeHalf lifeDating rangeRubidium-strontiumRb-87Sr-8747 by10m-4.6bUranium-leadU-238Pb-2064.5 by10m-4.6bUranium-leadU-235Pb-20771.3 my10m-4.6bThorium-leadTh-232Pb-20814.1 by10m-4.6bPotassium-argonK-40Ar-401.3 by.1m-4.6bCarbon-14C-14N-145730 y100-100,000Wednesday, October 26, 111999 GEOLOGIC TIME SCALECENOZOIC MESOZOIC PALEOZOICAGE(Ma)EPOCH AGEPICKS(Ma)MAGNETICPOLARITYPERIODHIST.ANOM.CHRON.5101520253035404550556065QUATER-NARYPLEISTOCENEMIOCENEOLIGOCENETRIASSIC JURASSIC CRETACEOUSPERMIANDEVONIANORDOVICIANSILURIANMISSISSIPPIAN PENNSYLVANIANCAMBRIAN*CARBONIFEROUSEOCENEPALEOCENEPLIOCENEPIACENZIANL0.011.83.65.37.111.214.816.420.523.828.533.737.041.349.054.857.961.065.0ELELMELMEELZANCLEANMESSINIANTORTONIANSERRAVALLIANLANGHIANBURDIGALIANAQUITANIANCHATTIANRUPELIANPRIABONIANBARTONIANLUTETIANYPRESIANDANIANTHANETIANSELANDIANCALABRIANHOLOCENETERTIARYPALEOGENENEOGENE1C1C2C2AC3C3AC4C4AC6C6AC6BC6CC7C8C9C10C11C12C13C15C16C17C18C19C20C21C22C23C24C25C26C27C28C29C7AC5C5AC5BC5CC5DC5E22A33A44A55B5A5C66A6B789101112131516171819202122232425282926277A6C5D5EAGE(Ma)EPOCH AGEPICKS(Ma)UNCERT.(m.y.)MAGNETICPOLARITYPERIODHIST.ANOM.CHRON.AGE(Ma)EPOCH AGEPICKS(Ma)PERIOD702602803003203403803604004204404604805005205408090100110120130140150160170180190210200 220230240NEOCOMIANLATEEARLYN.W. S.LATEEARLYMIDDLELATEEARLYMIDDLEMAASTRICHTIAN65248252256260269282296303290323327342354364370380391400412417419423428443449458464470485490500506512516495520 54371.3183.585.889.093.599.0112121127132137144151154164159CAMPANIANTATARIANUFIMIAN-KAZANIANKUNGURIANARTINSKIANSAKMARIANASSELIANGZELIANKASIMOVIANMOSCOVIANBASHKIRIANSERPUKHOVIANVISEANTOURNAISIANFAMENNIANFRASNIANGIVETIANEIFELIANEMSIANPRAGHIANLOCKHOVIANPRIDOLIANLUDLOVIANWENLOCKIANLLANDOVERIANASHGILLIANCARADOCIANLLANDEILIANLLANVIRNIANARENIGIANTREMADOCIANSUNWAPTAN*STEPTOEAN*MARJUMAN*DELAMARAN*DYERAN*MONTEZUMAN*SANTONIANCONIACIANTURONIANCENOMANIAN ALBIANAPTIANBARREMIANHAUTERIVIANVALANGINIANBERRIASIANTITHONIANKIMMERIDGIANOXFORDIANCALLOVIANBATHONIANBAJOCIANAALENIANTOARCIANPLIENSBACHIANSINEMURIANHETTANGIANNORIANRHAETIANCARNIANLADINIANANISIANOLENEKIANINDUANC31C32C33313233M0M1M5M10M12M14M16M18M20M22M25M29M3169176180195190202206210221234227248245242111444567788888888899999101233.2311RAPID POLARITY CHANGESPRECAMBRIANPROTEROZOICARCHEANAGE(Ma)EON ERABDY.AGES(Ma)75090016002500300034003800?100012501500175020002250250027503000325035003750LATEEARLYMIDDLELATEEARLYMIDDLELLMEEEEDCBALLLM30C3030C30C3434543Wednesday, October 26, 11PaleomagneticsEarth has a dipole magnetic field, with the direction in line with the axis of spin.When rocks form, they are permanently magnetized in the direction of the current magnetic latitude. Wednesday, October 26, 11Wednesday, October 26, 11Plate TectonicsWednesday, October 26, 11Wednesday, October 26, 11Wednesday, October 26, 11Wednesday, October 26, 11FossilsWednesday, October 26, 11A fossil is any recognizable evidence of preexisting life.Types of fossils:! (1) Trace fossils! (2) Preserved materialFossils are our only direct evidence ofwhat organisms looked like in the past.The fossil record is a biased one.Wednesday, October 26, 11Where is the time?Wednesday, October 26, 11Taphonomy: The study of the process of fossilization, from death of the organismto discovery by the paleontologist.Wednesday, October 26, 11Types of biases in the fossil record•Fossils with no hard parts are rarely preserved. Fossil record is mostly a record of shells and bones.•Organisms that lived in areas where they are likely to be preserved.•Time averaging of fossil beds.•Post-mortem transport, scavenging, Wednesday, October 26, 11Diatoms ForaminiferaMicrofossilsWednesday, October 26, 11“Invertebrates”Wednesday, October 26, 11VertebratesWednesday, October 26, 11StromatolitesWednesday, October 26, 11TransitionalFormsWednesday, October 26, 11Wednesday, October 26, 11Wednesday, October 26, 11Basilosaurus hind legWednesday, October 26, 11Ankle bones of the archaeocetes Rodhocetus (Eocene)on the left, a pronghorn (middle) and Artiocetus (right).Note the double-pulleyed astragalus. Other features in common are a notched cuboid and a prominent fibular facet.Wednesday, October 26, 11Tiktaalik roseae (late Devonian)Wednesday, October 26, 11Wednesday, October 26, 11Wednesday, October 26, 11Microfossils from the Apex Chert, North Pole, AustraliaAbout 3.465 billion years old, resembling filamentous cyanobacteriaWednesday, October 26, 11Stromatolite, North Pole deposits, Western Australiaabout 3.5 billion years oldWednesday, October 26, 11Extant stromatolite showing closeup of cyanobacteriaWednesday, October 26, 11Proterozoic (2.5 bya to 544 mya). Evolution of organisms with oxygenic photosynthesis caused an increase in oxygen levels. Rising oxygen levels in the world’s oceans caused the formation of iron oxide, often preserved in the banded iron formation. Wednesday, October 26, 11Eukaryotic milestones•2.7 bya: chemical traces of eukaryotic-type lipids in fossil organic matter (controversial).•2.1 bya: Grypania spiralis, the first fairly well-accepted fossil eukaryote•1.6-1.8 bya: origin of single-celled algae of unknown type, known as acritarchsWednesday, October 26, 11Grypania spiralis from MichiganWednesday, October 26, 11acritarchWednesday, October 26,
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