Dating Techniques Relative time given is relative to other strata or materials All you can say is that what you are dating is older than or younger than something else Absolute Year or range of years giving a date in numbers Relative Dating Techniques Stratigraphic analysis Law of Superposition Index fossil concept which is related to faunal succession Seriation stylistic frequency Relative Dating Techniques Law of Superposition We look at stratigraphy in undisturbed deposits deeper strata are older Strata layers We re looking at a profile view to see the stratigraphy Here is the original ground surface at A D 1200 Profile of postmold Relative dating technique Index fossil concept strata containing similar fossil assemblages must be of similar age Can trace faunal succession animal It helps to find some stratified faunal assemblages so that through the Law of Superposition you know which assemblage is older and which is more recent Then hopefully you will be able to obtain some absolute dates on your assemblages THEN if you ever find a particular faunal assemblage by itself you have a good idea to when it dates Or at least you know it is older than or younger than certain other faunal assemblages Faunal animal Relative dating technique Seriation as human behavior changes through time so do its material products Seriation is a technique to order artifacts in sequence Stylistic seriation Order one kind of artifact by similarities in style which reflect temporal change or spatial distance Frequency seriation Order assemblages by relative frequencies of artifact styles We assume a rise and fall in popularity of styles through time Stylistic seriation Order one kind of artifact by similarities in style which reflects temporal change or spatial distance Frequency seriation Order assemblages by relative frequencies of artifact styles We assume a rise and fall in popularity of styles through time Absolute Dating Techniques Radiometric techniques Radiocarbon C14 and AMS dating Potassium Argon K Ar or Argon Argon Ar Ar Other techniques Dendrochronology tree ring dating Archaeomagnetism Luminescence Absolute Dating Techniques Radiocarbon or C14 Three heavy carbon isotopes C12 C13 and C14 We are a carbon based planet During life an organism takes in C isotopes After death no C taken in Carbon isotopes form our tissues and organs British Museum After death of the organism C12 and C13 are stable can be used to reconstruct the diet of the organism C14 is unstable with a half life of 5 730 years it is radiometric the isotope degrades changes i e 5 730 years after an organism dies half the C14 isotopes taken in during life will have degraded In another 5 730 years half of those will have degraded Dependable for dating only when not too recent Upper limit reliable only to 50 000 years ago Radiocarbon Must be organic Need 10 grams Destroys what it dates Can date something organic that died not too recently historically up to 50 000 ya Costs ca 500 sample Not very accurate Gives a range of years At 1 sigma only a 2 in 3 chance of being correct ya years ago mya million years ago Gives date in RCYBP which must be calibrated to read in our calendrical system RCY radiocarbon years BP before present Willard Libby won the Nobel Prize for inventing radiocarbon dating at the end of WWII B P Before present A D 1950 Example 3000 RCYBP 50 Given 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 of actually 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 have Accelerator Mass Spectrometer AMS method of C14 dating More expensive but need only a few mg rather than the 10 g needed for regular C14 dating It s been used to date the Shroud of Turin Medieval fake In External Links under Dating you can read about it Summary of Relative Dating techniques Stratigraphic analysis Law of Superposition deeper strata are older Index fossil concept Strata with similar fossil assemblages must be of similar age Seriation Styles of artifacts change through time Which dating technique s could be used here to figure the age of the postmold 1 Stratigraphic analysis It must be younger than the original ground surface and older than the 2nd mound stage 2 C14 date on charcoal in it 3 Seriation It could be the same age as the artifacts in the same layer we know their age based on their style postmold Summary of Dating Techniques Which 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 excavators Index fossil concept is useful for dating early human fossil localities in South Africa where there has not been any volcanic activity but where we do have animal fossils along with the early human fossils
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