arch quiz 3

middle-level/middle-range theory

links human behavior to empirical data that are archaeological observable

analogy

noting similarities between two entities and inferring from that similarity that an addition attribute of one is also true of the other

FORMAL ANALOGY

similarities between the archaeological and modern cases

RELATIONAL ANALOGY

close cultural continuity or necessary function to justify analogy

experimental archaeology

experiments designed to determine the archaeological correlates of ancient behavior

• Tells us what past behaviors could or could not have happened in the past to produce certain material remains

taphonomy

study of natural processes acting on living things between the time of death and the moment of discovery; any chemical, biologic, physical activities that affect the organism’s remains

• For an archaeologist, taphonomy refers to how natural processes produce patterning in archaeological data

ethnoarchaeology

study of contemporary peoples to determine how human behavior is translated into the archaeological record

• Aims to generate explanation for artifact; derive theories and generalizations between behavior and material

chronology

the science of measuring time or ordering things in time

absolute date

date expressed in specific units of scientific measurement (days, years, etc.); absolute determinations attempting to pinpoint a discrete, known interval of time

relative date

dates expressed relative to one another (earlier, older, etc.) instead of in absolute terms

Birth of Christ, 1 AD → BC (Before Christ) and AD (Anno Domini, After Death) → Christian calendar

BCE (Before Common Era) and CE (Common Era) used to avoid cultural insensitivity

dates from radiocarbon dating use BP (Before Present)

• “Before Present” = “before 1950”

• we usually convert BP dates to BC/CE for anything from the last few thousand years

• for early prehistory, archaeologists use BP and “years ago” interchangeably (50 years won’t change much)

stratigraphy

a site’s physical structure produced by the deposition of geological and/or cultural sediments into layers or strata

• the underlying later was deposited first and is older than the overlying layer

• may be seeing the date of final burial or final deposition of an object, not the date it was used

GEOCHEMICAL RELATIVE DATING

- chemical tests to reveal whether one artifact has been absorbing or losing minerals for longer than other artifacts at the same site

- nitrogen, fluorine, and uranium content

- fluorine found in most groundwater → bones absorb the fluorine → bones replace hydroxyl with fluoride → degree of change is measure of elapsed time!

- fluorine dating says whether bones were buried at the same time

- “Piltdown Man” or Eonthropus Dawsoni

TYPOLOGICAL SEQUENCES

relies on two ideas:

1) products of a given period and place have a recognizable style

2) the change in style of artifacts are often gradual or evolutionary

- “like goes with like”!

- different types of artifacts change in style at different rates

- artifact types vary in the chronological distinctions they indicate

- fast-changing types are good chronological indicators

seriation

ordering of artifact-types through time

- places stylistic periods into a relative chronological sequence based on relative popularity

- contextual seriation vs. frequency seriation

contextual seriation

artifacts arranged according to frequencies of their co-occurance in specific contexts

• Governed by duration of different artifact styles

• Pioneered by Flinders Petrie

 frequency seriation

measuring changes in frequency of a style in an assemblage

• Assumes that styles gradually become more popular, reach a peak, then fade away (battleship curves)

• Assumes that, given a time period, a style popular at one site will also be popular at another

- James Deetz’ study of variation in gravestone designs in New England cemeteries

lexostatistics

studying the shift of common vocabulary words

glottochronology

date the divergence of two languages by the numbers of shifts

biostratigraphy

index fossils used to correlate sediments from different deposits

index fossils

artifactual (or ecofactual) time markers that are diagnostic and temporarily distinctive (only found in one time period)

ENVIRONMENTAL CHRONOLOGY

- Pleistocene chronology looks at climatic fluctuations

- glacials (periods of glacial advance) alternate with interglacials (warmer periods)

- Stadials and interstadials refer to minor fluctuations within these major phases 

- deep-sea cores and ice cores record climatic changes on a worldwide scale

- cores contain foraminifera (microscopic marine organisms) that can tell us sea temperature at the time they were alive

- can give relative and absolute dates

- pollen preserves well

- pollen samples enable palynologists to construct detailed sequences of past vegetation and climate

- localized sequences

- faunal dating relies on mammalian evolution

- changes in each species charted to create a rough sequence

- imprecise because species extinct in one area may continue for longer in another

- still useful for deeper time periods where any information is valuable

ABSOLUTE DATING

 absolute (or chronometric) dating tells us how hold something is in calendar years

- absolute dating relied on historical methods until the mid-20th century

- used calendars and chronologies made by the people of study

- some cultures without their own historical chronologies could be cross-dated (using finds from other areas with known calendars)

Terminus post quem (“the date after which”)

the deposit can’t be earlier than the inscription or date on the artifact

Terminus ante quem (“the date before which”)

the artifact can’t be younger than the context it’s found in

VARVES

- annual sediment deposits on shorelines of lakes

- 13,000 YA (years ago) – present

- first geochronological method to be developed in late 19th century

- geographically limited to areas affected by the annual melt/thaw cycle

dendrochronology

tree-ring dating

- tells you the year(s) the wood grew

- tree rings affected by annual fluctuations in rain, sunlight, and temperature

- useful for giving absolute dates for archaeological samples and calibrating radiometric dates

- two limitations:

• Only applies to trees in areas with pronounced seasonal variation

• Can only use wood from species that have a master sequence established all the way to present, was used by people in the past, and has a big enough sample that the ring sequence is long enough to give a unique match

dendrochronology = year wood grew

RADIOMETRIC DATING

- based on principle of radioactive decay

- most elements exist in more than one isotopic form

isotope

atoms of an element with different number of neutrons (e.g., ¹²C, ¹³C, ¹⁴C)

- radioactive isotopes decay into stable isotopes at a constant rate (radioactive decay)

half-life

how long it takes for half of the atoms of an isotope to decay; time needed for 50% of parent isotope to decay into daughter isotope

RADIOCARBON DATING

- carbon-14 (¹⁴C) dating assigns ages to organic materials

- measures decay of carbon-14 isotope, which has a half life of 5,730 years

- amount of ¹⁴C left in organic remains to determine when the plant or animal died

- can be used anywhere in any climate IF there is organic material

- can establish chronologies for prehistory

- with AMS, can use tiny samples

¹⁴C = last time when sample grew or when it died

beta-particle counting

cheap, large samples (destructive), takes long time

Accelerator Mass Spectrometry (AMS)

expensive, small samples (relatively non-destructive), quick, more accurate

¹⁴C content of a sample:

- calculated in relation to the year 1950 as “BP”

- years given with the lab and analysis number

- accuracy reported as probable error because radiocarbon dates are statistical estimates of the age of the sample

• 3700 ± 100 BP (P-685)

- dates are lab determinations, not calendar years, and so they are “uncalibrated”

- BP can be calibrated to calendar years

- potential problems:

• Contamination before sampling

• Contamination during/after sampling

• Context of deposition

• Date of context

outer effective range

about 40–50,000 BP

inner effective range

about 300–500 BP, depending on method (beta-counting or AMS)

RADIOPOTASSIUM DATING

- decay of ⁴⁰K into ⁴⁰Ar (potassium-argon dating) or ⁴⁰Ar to ³⁹Ar (argon-argon dating)

- most effective for early archaeological record using volcanic rocks no younger than 100 KYA (thousands of years old)

- ⁴⁰Ar-³⁹Ar dating for more precise dates or younger dates

- dates for rock samples, not archaeological material

- archaeological remains can lie on and under volcanically-formed geological strata

- can date the sediments or rocks that sandwich the archaeological remains

half-life of ⁴⁰K

1.3 billion years

URANIUM-SERIES DATING

- 2 radioactive isotopes of uranium (U-238, U-235) that decay into two daughter elements (thorium-230, proctactinium-231)

- daughter elements have useful half-lives and uranium isotopes are water-soluble

- used to date calcium carbonate

• Rocks, bones, teeth, artifacts

- useful for dates from 50 to 500 KYA

TRAPPED ELECTRON DATING

• Thermoluminescence (TL)

• Electron-Spin Resonance (ESR)

• Optically-Stimulated Luminescence (OSL)

- amount of radiation received by the sample to be dated

- measures electrons trapped in crystalline rocks and bones

- assumes rate of radiation per year is constant over time

- age = total radiation dose/annual radiation dose

Thermoluminescence (TL)

considered most reliable of the TED methods but less precise than radiocarbon

- TL can go back 100 KYA

- TL done on minerals that were exposed to high temperatures

OSL (optically-stimulated luminescence)

 based on how most minerals contain electron traps that were emptied with exposure to sunlight

ESR (electron-spin resonance)

can be used with materials that decompose when heated

• Tooth enamel, etc.

• Can go back to 1,000,000 years, but accuracy concerns

DATING SUMMARY

- all techniques (except dendrochronology) produce estimates of age

- techniques based on physical processes that occur at a fixed rate

- techniques give ages of different events

- the techniques provide estimates of the age of different events… those events might not be the same time as the behavior you want to date!!!

K-Ar

when molten rock crystalized

TR

when sample was heated above a certain temperature