Arky Midterm 1 - Dating Methods & Middle-Range Theory

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Analogy

Back 1

- a process of reasoning that assumes if objects have similar attributes, then they will share other similarities as well

- also called middle-range theory

Hint 1

comparing objects

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Middle-range Theory

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- Encompasses ethno-history, ethno-arky, and experimental arky

- objective theoretical devices for forging a link between the dynamic living systems of today, and the static arky record of the past

- generally structuralist and processualist

Hint 2

There are 3 subtypes of theory

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Ethnohistory

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- thestudy of the past using indigenous historical records and oral histories

- example: Mayan/Aztec pictographs of atlatls, and Spanish writings that describe atlatls; examples of specimens that survived in Peru, southern States, gifts to Spain and Popes, and Magdalenian Europe

Hint 3

Subset of middle-range theory/analogy

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Ethnoarchaeology

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- the study of living societies to aid in understanding and interpreting the arky record

- began in 1970s:

--- Richard Lee studying the !Kung San people of the Kalahari desert

--- Lewis Binford studying the Nunamiut Eskimo

--- continued use of the atlatl in Inuit, Aleut, and Tlingit cultures

Hint 4

Subset of middle-range theory/analogy

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Experimental Archaeology

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- controlled, modern experiments with ancient tech and material cultures tocompare with observations in the arky record, as a basis for interpreting the past

- began in 1700's Europe, with blowing peat-bog bronze horns (Robert Ball of Dublin)

- modern lithics experiments

- Thor Heyerdahl's failed Kon Tiki experiment in 1950

- recreations of atlatls to examine the cause/use of weights tied to the shaft

Hint 5

Subset of middle-range theory/analogy

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Absolute Dating

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- a dating method that gives a specific calendar date, or a date range.

- Methods include: Historical Records & Calendars, and Cross-Dating from objects of known age.

- Also, dendrochronology, radiocarbon dating, etc, fall under absolute dating, even though they often yield date ranges instead of specific dates.

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Historical Records & Calendars

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- Method of Absolute Dating

- Uses historical records (tablets, decrees, calendars, religious cycles, etc) to specifically date events

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Epigraphers

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- experts in decoding ancient writing systems

- They draw on linguistics and code breaking methods

Hint 8

code-breakers

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Cross-dating

Back 9

- Method of Absolute Dating

- Uses objects of known historical age to date other arky finds: coins, pipes of a certain style, etc

- Can be problematic due to collecting - people may hang onto coins for a long time, but at least we know the site can't be earlier than the coin that was found there.

Hint 9

previously dated items/artifacts

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Dendrochronology

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- Dates samples roughly 1500 AD to 50k years old, in certain regions.

- A dating method that matches the annual growth rings of an arky recovered wood sample to an established temporal sequence

- Looks at the width of the rings, to establish sequences of wet and dry years.

- Need multiple overlapping samples to help establish the sequence.

- Specific only to a certain region

- Can't establish sequences for some regions, because their wet/dry seasons are not well demarked (ie: arctic or tropical environs) or the wood of the local trees don't clearly show rings.

Hint 10

Tree-Ring Chronology

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The “Old Wood Problem”

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In the American SW, peoplewould re-use older house beams, sometimes even taking thebeams of their old houses with them, making the beams older than the structures they are found in, resulting in much earlier (incorrect) dates for the site.

Hint 11

American SW

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Radiocarbon Dating

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- Dates samples from 1950 to 50k years old

- Measures the proportion of radioactive carbon to non-radioactive carbon in a sample

- Only works on organic remains: wood, charcoal, ivory, plants, shell, bone, cloth, fibre, etc

Hint 12

1950 to 50k years old

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AMS Dating

Back 13

- Accelerator Mass Spectrometry

- Dates samples from 1950 to 50k years old

- A newer, more accurate form of Radiocarbon dating, that results in a narrower date range

- Uses very small samples

Hint 13

1950 to 50k years old

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C14

Back 14

- Cosmic rays bombard atmosphere Nitrogen 14 loses a proton and becomes Carbon 14, which is radioactive

- C14 is oxidised and becomes CO2 (with the C being radioactive C14)

- The radioactive CO2 is photosynthesized into plants, which are eaten by animals

- The plants/animals die, and no more CO2 is taken in; decay begins.

Hint 14

describe where it comes from

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C14 Half-Life

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Carbon 14 decays half of its remaining radiocarbon every 5,730 years

Hint 15

5,730 years

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C14 Calibration

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- Because of atmospheric C14 fluctuations, samples can be dated to multiple ranges (opposite sides of the same curve, and multiple curves through history)

- C14 date ranges have to be calibrated with the 'OxCal' program to get the AD/BC range at a 1 sigma or 2 sigma error margins (the p% shows which range is more likely)

- 'OxCal' is continuously updated with ice cores, dendrochronology, etc

- 1 sigma is less accurate, with a smaller range

- 2 sigma is more accurate, with a larger range

- Date ranges from multiple samples from the same site can be averaged together to get a narrower overall range for the site.

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Electron Spin Resonance (ESR) Dating

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- Dates samples up to 1 million years old

- Used for bone, enamel, shell, and other delicate materials that we don't want destroyed

- Measures electrons trapped in a material, without heating

- More expensive than ThermoL

Hint 17

up to 1 million years old

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Thermoluminescence Dating

Back 18

- Dates samples 50k to 20k years old

- Good for pottery, brick, tile, terra cotta, etc - things that were heated only once

- The fragment is reheated, and the newly emitted photons are measured

- Will tell you when the item was made; not when it was deposited in the strata

- Used to authenticate pottery or detect forgeries

Hint 18

50k to 20k years old

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Archaeomagnetic Dating

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- Only for dating features that have been fired (hearths, ovens, kilns, furnaces, etc)

- During firing the particles align with the earth's magnetic poles

- By finding the angle of magnetic declination from the current poles, we can understand where the previous magnetic north was (make a thin section and look at it under a microscope)

- Comparing the declination with historic inclination deviation, we can identify the date the feature was fired

- If the pole was in the same place multiple times, the sample could be dated to multiple ranges, just like radiocarbon dating.

Hint 19

fired features only

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Potassium-Argon (K-Ar) Dating

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- Dates samples 50k to 3 billion years old; picks up where radiocarbon leaves off at 50k

- Error margins of +/- 1k years

- For dating the rock deposit

- Measures the rate of decay of radioactive Potassium (40K) into Argon (40Ar)

- Must date the deposit where the artifact lies! If you date the artifact, you date when the rock was formed, not when the artifact was discarded

Hint 20

50k to 3 billion years old

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Uranium Series Dating

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- Dates samples 50k to 1 million years old (overlaps with ESR and K-AR dating)

- Measures the decay of uranium isotopes 235 and 238 found in calcium carbonate deposits, such as limestone, flowstone, stalagmites, stalactites, etc

- Good for caves!

- Must date the deposit where the artifact lies! If you date the artifact, you date when the rock was formed, not when the artifact was discarded

Hint 21

50k to 1 million years old

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Fission-track Dating

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- Dates samples 100k to 20 million years old

- Measures the number of uranium fission tracks (trails of damage from particles emitted by decaying uranium) in a polished thin section

- Works on volcanic rocks - obsidian, basalt, anything igneous, some metamorphic

- Must date the deposit where the artifact lies! If you date the artifact, you date when the rock was formed, not when the artifact was discarded

Hint 22

100k to 20 million years old

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Relative Dating

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- Establishes relative chronological relationships between sites and cultures.

- Prior to 1948 (Walter Taylor's invention of C14 dating), this was the only way to date things!

- There are two main methods: Stratigraphy and Seriation

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Stratigraphy

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- A Method of Relative Dating

- The study of different rock or soil formations that are laid down in successive layers, or 'strata'

- Complicating factors are Mixing, Filling, Unconformities, and Collecting

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Mixing

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- The mixing of strata caused by digging operations

- May be indicated by a combination of colour or different artifact types.

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Filling

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- A depositional unit that was laid down to alter the original ground level

- Often found coinciding with digging.

- Could be caused by a tree falling over (its roots rip out and the depression gets filled with soil from newer strata), or the laying of a path, or floor, etc.

- Usually is an intentional, human action.

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Unconformities

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Natural filling - temporal breaks in the stratigraphic sequence as a result of a change that cause deposition to cease for a period of time

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Collecting

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- The acquisition and reuse of ancient objects

- Finding an older artifact in a newer deposit can indicate collection

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Horizon Line

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the line between distinct strata

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Law of Superposition

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lower strata are deposited before higher strata (singular of 'strata' is 'stratum'), and are therefore older

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Law of Strata Identified by their Contents

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- The 'horizons' between strata can be distinguished by:

--- differences in the various kinds of objects and associations they contain (ie: newer layers will have new types of stuff: 'iron age' pun)

--- differences in the frequencies of various cultural materials (ie: older items will decrease in frequency in progressively newer layers)

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Seriation

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- A Method of Relative Dating

- A technique for ordering artifacts or assemblages by their structure or design, where the most similar are place adjacent to each other in a series

- Seriation is combined with stratigraphy to see how styles change through time and subsequent depositional layers.

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Stylistic Seriation

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- Artifacts or other data are ordered chronologically according to stylistic similarities.

- Example: jars that gradually get flatter bottoms, or dishes that get bigger, etc, according to the change in needs/purpose

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Frequency Seriation

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- Uses percentages of artifacts and their features to develop cultural sequences (ie: an older style will decrease in percentage of finds in newer layers)

- It's very rare for stylistic changes to happen suddenly and cause a horizon; usually change is gradual.

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Battleship curves

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- Graphing of frequency seriation, showing the increase and decrease of artifact styles

- Examples: New England gravestone designs, or Zuni pottery

- If the data is incomplete, the curve may suddenly drop off; of the drop-off my indicate a change in customs, a trade restriction, or a change in the availability of materials.