Archaeological Sciences

1
Archaeological Sciences

• An Introduction
• Created By Margaret Blome
• U of Arizona IGERT Graduate Student
• 6/11/07

2
Archaeology

• The study of past cultures through their material
  remains (Arch 101)

3
Archaeology

• The study of past cultures through their material
  remains (Arch 101)
• Scientific study of material remains of past
  human life and activities (Encyclopedia
  Britannica)

4
Archaeology

• The study of past cultures through their material
  remains (Arch 101)
• Scientific study of material remains of past
  human life and activities (Encyclopedia
  Britannica)
• The recovery and study of material objects, such
  as graves, buildings, tools, artworks, and human
  remains, to investigate the structure and
  behavior of past cultures (Science Dictionary)

5
Archaeological Sciences

• The study of human cultures through the recovery,
  documentation and analysis of material remains
  and environmental data including
• architecture, artifacts, biofacts, human remains,
  and landscapes (Wikipedia)
• The use of the hard sciences to understand
  archaeological questions. (Meg)

6
Archaeological Sciences

• Absolute Dating
• Radiometric
• 14C
• Uranium series (U/Th)
• K-Ar or Ar-Ar
• Cosmogenic Radionuclides (CRNs)
• 10Be
• 26Al
• 3He
• Luminescence
• OSL Optically Stimulated Luminescence
• TL Thermo Luminescence

• Geoarchaeology
• Landscape reconstruction
• Site formation or destruction processes
• Catastrophic events
• Paleoclimatology
• Reconstructing past climates
• Soil Sciences
• Paleobiology
• Ancient diet and subsistence
• Ancient DNA
• Material Science
• Stone, bone, metal artifacts

7
Radiometric Dating Vocabulary

• Isotopes forms of a single element (same
  protons) with different numbers of neutrons
• Parent the isotope that undergoes nuclear decay
• Daughter the isotope that results from nuclear
  decay
• Parent/Daughter ratio used in U/Th dating
• Radioactive Decay the process by which an
  unstable nucleus loses energy by emitting
  radiation.
• Process is random on atomic level, but decay rate
  is predictable
• Half-life the amount of time it takes for half
  of an initial quantity of unstable isotopes to
  decay.

8
Radiometric Dating

• Radiometric Isotopes (Non-stable)
• 14C (Radiocarbon)
• U/Th (Uranium series)
• K/Ar (Potassium-Argon)

238U 234U E,
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Periodic Table of Elements

• Highlighted are the main elements used in dating

10
Essential InformationThe isotopes used in
archaeology
Isotope system ½ Life Parent Daughter
Radiocarbon 5730 yrs 14C (Carbon) 14N (Nitrogen)
Uranium series 4.5 billion yrs 244,000 yrs 238U 234U 234U 230Th
K-Ar or Ar-Ar 1.3 billion yrs 40K 40Ar
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Radiocarbon dating in depth

• Why is 14C useful?
• Production 14C is created from 14N in the
  atmosphere due to cosmic ray bombardment
• Absorption, into all living things
• Decay Beginning of the radiocarbon clock at
  death

• Problems
• Production rate varies over time
• Calibration Required
• Difference between 14C age on land and in the
  ocean Reservoir Effect
• Can only date objects containing carbon.
• Trees/wood/charcoal
• Plants/seeds
• Bone/hair/teeth
• Shell/coral

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Carbon 14 production in atmosphere
147N 10n 146C 11p
Carbon 14 absorption into living things
13
14C Absorption into carbon-based life
Coral living
ancient/fossil
14
Plants, Trees Charcoal
15
People Animals!
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A Current amount of 14CA0 Initial amount of
14C (amount absorbed at time of death)e
Mathematical constant (2.71828)? Constant
(ln(2) / half life)t Time
A/A0 e-?t
17
Measurement of 14C using AMS (Accelerator Mass
Spectrometry)
Images from UA physics website
Sample pretreatment in UA laboratory
18
Sample pretreatment methods

• Depends on specific material to be dated
• Charcoal
• Plant material
• Soil
• All treated with ABA process
• Acid, Base, Acid baths

• Pretreatment also depends on analytical method to
  be used
• AMS measurement needs less than 1 gram of sample
• Conventional method requires more sample

19
Measurement of 14C

• Conventional Method
• Requires more sample
• Takes a longer time
• Cheaper!
• Process
• Measures emission of beta particles from sample
  over time
• Beta particles are emitted during decay

• Accelerator Mass Spectrometer (AMS)
• Requires less sample
• Faster results!
• More expensive
• Process
• Ionize carbon sample
• Puts sample into gaseous state
• Magnets bend flow of sample and separates
  according to mass and charge
• Actually sorts and counts isotopes

20
Uranium series dating intro

• Dating range for U/Th system
• Up to 450,000 years
• Fills the gap between K/Ar and radiocarbon dating
• Range for 234U/238U
• 10,000 2 million yrs
• Why this works?
• Uranium substitutes for Calcium in calcite

• Materials that can be dated with this system
• Cave deposits
• Coral
• CaCO3 (Calcite)
• Sometimes this includes bone!

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Coral living
ancient/fossil
23
K-Ar dating in depth

• How it works
• Used in locations with periodic volcanic activity
• Absolutely date layers of ash that bound
  stratigraphic layer with archaeological remains
• Dates from 500,000 to millions of years

24
K-Ar datable materials

• Volcanic ash

25
Essential Isotope InformationReview
Isotope system ½ Life Date Range from to Date Range from to
14C 5730 yrs 50,000 years Present
234U/238U 234U/230Th 4.5 billion yrs 244,000 yrs 2 million yrs 450,000 yrs 10,000 yrs present
K-Ar 1.3 billion yrs Millions of yrs 500,000 yrs
26
Non radiometric dating methods

• Luminescence TL and OSL
• Can be used on burnt flint and quartz sediment
• Cosmogenic Radionuclides (CRNs)
• Accumulated amount can be used to date exposed
  rock surfaces

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Quartz Sand
Flint tools
Bare Rock
Sand Dune