Archaeology 5:Archaeology 5:

When Is It Dated?When Is It Dated?

Dating Methods and Dating Methods and ArchaeologyArchaeology

ProgrammeProgramme

Lecture students (‘From the Ground Lecture students (‘From the Ground Up’) on Sunday, October 2nd, DMS Up’) on Sunday, October 2nd, DMS 1120, 2 pm! 1120, 2 pm!

Workshop of next Thu & Tue: Workshop of next Thu & Tue: ‘Practicum Artefacts’!‘Practicum Artefacts’!

Ch. 4Ch. 4

TimeTime

Solar system; some countries still use Solar system; some countries still use lunar systemlunar system

BC (Before Christ)/AD (Anno Domini)BC (Before Christ)/AD (Anno Domini) BCE/CE (Before Common BCE/CE (Before Common

Era/Common Era)Era/Common Era) BP (Before Present, used in Science)BP (Before Present, used in Science)

‘‘present’ = 1950present’ = 1950

RelativeRelative DatingDating

1. Stratigraphy: Law of Superposition, the 1. Stratigraphy: Law of Superposition, the layer that has been deposited on top layer that has been deposited on top of another layer is usually laterof another layer is usually later

For example: Harris matrixFor example: Harris matrix

2. Typology: mostly with potsherds, but 2. Typology: mostly with potsherds, but also for example stone tools; still also for example stone tools; still very useful for dating in prehistorical very useful for dating in prehistorical sitessites

Principle:Principle:a.a. Artefacts of a given time and place Artefacts of a given time and place

have a distinctive style: ‘Like goes have a distinctive style: ‘Like goes with like’ with like’

b.b. Artefacts slowly change/evolve over Artefacts slowly change/evolve over time (Darwin: evolutionary theory)time (Darwin: evolutionary theory)

Oscar Montelius (19Oscar Montelius (19thth century): century): established relative chronology for established relative chronology for Bronze Age Europe on the basis of Bronze Age Europe on the basis of typological methodtypological method

Relative Dating (2)Relative Dating (2)3. Seriation: looking at groups of finds together (pots/tools etc.: 3. Seriation: looking at groups of finds together (pots/tools etc.:

assemblages) and arranging them in chronological assemblages) and arranging them in chronological sequencessequences

a.a. Contextual Seriation: Flinders PetrieContextual Seriation: Flinders PetrieArranging of artefacts according to duration: best Arranging of artefacts according to duration: best arrangement is that in which the greatest number of arrangement is that in which the greatest number of artefacts has shortest duration artefacts has shortest duration

b.b. Frequency SeriationFrequency SeriationMeasuring changes in the proportional abundance of a Measuring changes in the proportional abundance of a certain style: battleship curves (some objects are more certain style: battleship curves (some objects are more popular at a given time); then relate these curves to other popular at a given time); then relate these curves to other sites, and you can come to a whole chronological systemsites, and you can come to a whole chronological system

4. Pollen dating: chronological sequences in pollen (grains)4. Pollen dating: chronological sequences in pollen (grains)As detailed (absolute dated) systems of such pollen exist for a As detailed (absolute dated) systems of such pollen exist for a

large part of the earth, a pollen analysis can get a very large part of the earth, a pollen analysis can get a very precise dating precise dating

• Methods 1-3 were developed in ‘Beginnings of Methods 1-3 were developed in ‘Beginnings of Archaeology’ period (19Archaeology’ period (19thth century) or in the century) or in the classificatory-historical periodclassificatory-historical period

• Method 4 mostly in the second half of the 20Method 4 mostly in the second half of the 20thth century (in accordance with New century (in accordance with New Archaeology)Archaeology)

• These methods are still often used, but These methods are still often used, but always together with an absolute dating always together with an absolute dating system; mostly there exist databases of system; mostly there exist databases of relative chronological systems that have been relative chronological systems that have been absolutely datedabsolutely dated

Typological sequences

Contextual seriation

Frequency seriation

Absolute Dating1. Conventional Historical Chronology: based on historical

texts, mainly Bible but also Egyptian king lists; used in Speculative PeriodSetbacks:a. chronological system may be incomplete or inaccurateb. chronological system must be linked to our own chronological system (Gregorian calendar)c. individual artefacts in dig need to be related to chronological systemCross dating through imports:* Egyptian contexts can be dated absolutely; Greek imports in those contexts were then made before that date (terminus ante quem)* Terminus post quem: a coin found in a context, dating to, say, 10 CE, dates the context to after that date, because it was in use in 10 CE and later

After WO II: new scientific After WO II: new scientific methodsmethods

(selection):(selection):2. Radiocarbon Dating (C-14 Dating): Willard Libby 1949Principles:- Proportion of radiocarbon (C-14 or 14C) in atmosphere is

stable because of cosmic radiation- Goes into all living organisms: from plants to animals to

Man- When organism die, radiocarbon decreases in a

proportioned wayErgo: if we measure the proportion of 14C in any organic

remains we can calculate the exact date

Advantages:- Is a worldwide dating method- Covers the last 50,000 years- Very small samples can be submitted (in mg.’s!):

Accelerator Mass Spectrometry (AMS)

Disadvantages:Disadvantages:1.1. Sample contamination: errors before, during or Sample contamination: errors before, during or

after sampling; archaeological context after sampling; archaeological context unknown; date of context differs from sample unknown; date of context differs from sample (e.g. when sample has been reused)(e.g. when sample has been reused)

2.2. Mistakes in laboratoriesMistakes in laboratories3.3. Cosmic radiation fluctuates: before 1000 BCE Cosmic radiation fluctuates: before 1000 BCE

the datings are problematic and increasingly the datings are problematic and increasingly younger; this could be partly fixed by using tree younger; this could be partly fixed by using tree ring dating (see next) but only covers last 8000 ring dating (see next) but only covers last 8000 yearsyears

Because of this, usually a standard deviation is Because of this, usually a standard deviation is given (68%): 3700 +/- 100 BPgiven (68%): 3700 +/- 100 BP

NB: Adapted dates are called calibrated dates!NB: Adapted dates are called calibrated dates!

3. Tree Ring Dating (Dendrochronology): developed in 1960sPrinciples: - each tree gets a new ring every year (with every cycle of

seasons)- Rings become narrower when they are older- Growth of tree (and ring) depends on climatic change- Similar trees in same area produce the same tree ring patternErgo: if you include thickness between rings in a graph – you can

work backwards and establish a sequence (see p. 139!)

Advantages:- Covers last 8000 years- Very detailed: can date a piece of wood within a year- Can correct or calibrate radiocarbon dates

Disadvantages:Disadvantages:1.1. Not in tropics (there difference in tree ring Not in tropics (there difference in tree ring

thickness is not clearly defined), so not worldwidethickness is not clearly defined), so not worldwide2.2. Only wood that was used in pastOnly wood that was used in past3.3. Only wood for which there exists a long (regional) Only wood for which there exists a long (regional)

sequence from the present day backwardssequence from the present day backwards4.4. Sapwood (outermost rings) must be thereSapwood (outermost rings) must be there5.5. It only gives the felling date of the tree, problem: It only gives the felling date of the tree, problem:

wood might be older or younger than building in wood might be older or younger than building in which it was reused: when the wood came from which it was reused: when the wood came from somewhere else and was reused, the building somewhere else and was reused, the building may be younger; when the wood was used, e.g. may be younger; when the wood was used, e.g. for a repair, in an existing building, the building for a repair, in an existing building, the building may be oldermay be older

Thermoluminescence Dating (TL)

Advantages: Advantages: - Dates inorganic remains (pottery)Dates inorganic remains (pottery)- Dating goes beyond 50,000 yearsDating goes beyond 50,000 years

Disadvantage: less accurate than radiocarbon datingDisadvantage: less accurate than radiocarbon dating

For objects exposed to fire (ceramics, burnt flint)For objects exposed to fire (ceramics, burnt flint)

Principles (p. 155):Principles (p. 155):- electron traps (TL clock) set to zero after heatingelectron traps (TL clock) set to zero after heating- TL accumulatesTL accumulatesErgo: if we heat object again we can determine age (the older, Ergo: if we heat object again we can determine age (the older,

the higher amount of TL)the higher amount of TL)

Thera (Santorini)

Dates proposedDates proposed

Connection with end of Minoan Civ. In Connection with end of Minoan Civ. In 1450 (late Minoan 1B); date corrected 1450 (late Minoan 1B); date corrected because of shards from site itself to because of shards from site itself to 1500 BCE (late Minoan 1A)1500 BCE (late Minoan 1A)

Tree ring sequence: 1628-1626 BCETree ring sequence: 1628-1626 BCE Ice cores (acidity peaks): different Ice cores (acidity peaks): different

dates between 1645 (incorrect) and dates between 1645 (incorrect) and 1390 BCE1390 BCE

Radiocarbon date: 1663 and 1599 Radiocarbon date: 1663 and 1599 BCE/1627-1600 BCEBCE/1627-1600 BCE

Thucydides: Greek historian fifth century BCE

Carthage, modern Tunis, North-Africa: Phoenicians

Implications:Implications:

Redating of Greek pottery (relative Redating of Greek pottery (relative chronology)chronology)

Greek colonisation a longer process, Greek colonisation a longer process, contacts probably started already in IX contacts probably started already in IX BCE and took until VII BCEBCE and took until VII BCE

Iron Age starts earlier, hence changes less Iron Age starts earlier, hence changes less abruptabrupt

‘‘Dark Ages’ become more of Dark Ages’ become more of transformational period between Bronze transformational period between Bronze and Iron Agesand Iron Ages