Slide 1Slide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Dating TechniquesRelative: time given is relative to other strataor materials. All you can say is that what youare dating is older than or younger than something elseAbsolute: Year or range of years, giving adate in numbersRelative Dating TechniquesStratigraphic analysis (Law of Superposition)Index fossil concept, which is related to faunal successionSeriation (stylistic, frequency)Relative Dating TechniquesLaw of Superposition We look at stratigraphy: in undisturbed deposits, deeper strata are older.Here is the originalground surface atA.D. 1200Profile of postmoldStrata (layers)We’re looking at aprofile viewto see thestratigraphyIndex fossil concept: strata containing similar fossil assemblages must be of similar age. Can trace faunal succession (animal) Relative dating techniqueIt helps to find some stratified faunal assemblages,so that through the Law of Superposition you knowwhich assemblage is older and which is more recentThen hopefully you will be able to obtain someabsolute dates on your assemblagesTHEN, if you ever find a particular faunal assemblageby itself, you have a good idea to when it datesOr at least you know it is older than or younger thancertain other faunal assemblagesFaunal = animalRelative dating techniqueSeriation: as human behavior changesthrough time, so do its material products.Seriation is a technique to order artifactsin sequence.Stylistic seriation: Order one kind ofartifact by similarities in style, which reflect temporal change or spatial distance.Frequency seriation: Order assemblagesby relative frequencies of artifact styles. Weassume a rise and fall in popularity of stylesthrough time.Stylistic seriationOrder one kind of artifact by similarities in style, which reflects temporal change or spatial distance.Frequency seriationOrder assemblagesby relative frequencies of artifact styles. Weassume a rise andfall in popularity ofstyles through time.Absolute Dating TechniquesRadiometric techniques:Radiocarbon (C14) and AMS datingPotassium/Argon (K/Ar) or Argon/Argon (Ar/Ar)Other techniques:Dendrochronology (tree ring dating)ArchaeomagnetismLuminescenceAbsolute Dating TechniquesRadiocarbon or C14Three heavy carbon isotopes: C12, C13, and C14Carbon isotopes form our tissues and organsBritish MuseumWe are a carbon-basedplanet:During life, an organismtakes in C isotopesAfter death, no C taken inAfter death of the organism:C12 and C13 are stable – can be used toreconstruct the diet of the organismC14 is unstable, with a half life of 5,730 years(it is radiometric – the isotope degrades/changes)Dependable for dating only when not too recent; Upper limit reliable only to 50,000 years agoi.e., 5,730 years after an organism dies, half theC14 isotopes taken in during life will have degradedIn another 5,730 years, half of those will have degradedRadiocarbonMust be organicNeed 10 grams+Destroys what it datesCosts ca. $500/sampleNot very accurate:Gives a range of years:At 1 sigma, only a 2 in 3 chance of being correctCan date somethingorganic that died nottoo recently (historically) up to 50,000 ya ya = years agomya = million years agoGives date in RCYBP,which must be calibratedto read in our calendrical systemRCY = radiocarbon yearsBP = before presentWillard Libby won the Nobel Prize forinventing radiocarbon dating at the end of WWIIB.P. Before present = A.D. 1950Example: 3000 RCYBP + 50Given that BP = 1950,1950 - 3000 = 1050 B.C.What is that range or +/- given ???That’s the level of accuracy for this particular sample(the +/- is different for each sample: 50 is pretty good)At 1 sigma (as given), the date has a 2 in 3 chance ofactually falling within the range given, i.e., 1100-1000 B.C. At 2 sigma (double the +/-), the date has a 99%chance of being correct (1150 - 950 B.C.)Now haveAccelerator Mass Spectrometer (AMS) method of C14 dating: More expensive, but need only a few mgrather than the 10 g needed for regular C14 datingIt’s been used to date the Shroud of Turin!Medieval fake!In External Links under Dating, you can read about itSummary of Relative Dating techniquesStratigraphic analysis Index fossil conceptSeriation (Law of Superposition: deeper strata are older) (Strata with similar fossil assemblages must be of similar age)Styles of artifacts change through timeWhich dating technique(s)could be used hereto figure the ageof the postmold?postmold1. Stratigraphic analysis:It must be younger thanthe original ground surfaceand older than the 2ndmound stage.3. Seriation:It could be the same ageas the artifacts in the samelayer, & we know their agebased on their style.2. C14 date on charcoal in itSummary ofDating TechniquesWhich dating techniques are used where and when?Stratigraphic analysis is used at EVERY archaeological site and EVERY fossil locality, on a daily basis by the excavatorsIndex fossil concept is useful for dating early humanfossil localities in South Africa, where there has notbeen any volcanic activity but where we do have animal fossils along with the early human
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