archaeological sciences an introduction created by: margaret blome u of arizona igert graduate...
Post on 13-Jan-2016
219 Views
Preview:
TRANSCRIPT
Archaeological Sciences
An IntroductionCreated By: Margaret Blome
U of Arizona IGERT Graduate Student6/11/07
Archaeology• The study of past cultures through their material
remains (Arch 101)
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)
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)
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)
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
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.
Radiometric Dating
• Radiometric Isotopes (Non-stable)– 14C (Radiocarbon)
– U/Th (Uranium series)
– K/Ar (Potassium-Argon)
14C 14N + Energy238U 234U + E, 234U 230Th + E
40K 40Ar + Energy
Highlighted are the main elements used in dating
Periodic Table of Elements
Essential Information:The isotopes used in archaeologyIsotope system
½ Life Parent Daughter
Radiocarbon 5730 yrs 14C
(Carbon)
14N
(Nitrogen)
Uranium series
4.5 billion yrs
244,000 yrs
238U234U
234U230Th
K-Ar or
Ar-Ar
1.3 billion yrs 40K 40Ar
Radiocarbon dating: in depth
• Why is 14C useful?1. Production – 14C is
created from 14N in the atmosphere due to cosmic ray bombardment
2. Absorption, into all living things
3. 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
Carbon 14 production in atmosphere
Carbon 14 absorption into
living things
147N + 1
0n = 146C + 1
1p
14C Absorption into carbon-based life:
Coral – living
& ancient/fossil
Plants, Trees & Charcoal
People & Animals!
A/A0 = e-λt
A – Current amount of 14CA0 – Initial amount of 14C (amount absorbed at time of death)e – Mathematical constant (2.71828…)λ – Constant (ln(2) / half life)t – Time
Radiocarbon Decay
00.10.20.30.40.50.60.70.80.91
0 5730 11460 17190 22920 28650 34380
Time
Rat
iot = 0
t = 1
t = 2t = 3
t = 4 t = 5t = 6
Exponential Decay
Measurement of 14C using AMS (Accelerator Mass Spectrometry)
Sample pretreatment in UA laboratory
Images from UA physics website
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
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
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!
Coral – living
& ancient/fossil
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
Ash
Ash
Artifacts
River cobbles
Sterile dirt
Modern surface
K-Ar datable materials
• Volcanic ash
Essential Isotope Information:Review
Isotope system
½ Life Date Range
from to 14C 5730 yrs 50,000 years Present
234U/238U234U/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
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
Sand Dune Bare Rock
Quartz Sand
Flint tools
top related