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

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 14 C Uranium series (U/Th) K-Ar or Ar-Ar –Cosmogenic Radionuclides (CRNs) 10 Be 26 Al 3 He –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) – 14 C (Radiocarbon) –U/Th (Uranium series) –K/Ar (Potassium-Argon) 14 C 14 N + Energy 238 U 234 U + E, 234 U 230 Th + E 40 K 40 Ar + Energy

Highlighted are the main elements used in dating Periodic Table of Elements

Essential Information: The isotopes used in archaeology Isotope system ½ LifeParentDaughter Radiocarbon5730 yrs 14 C (Carbon) 14 N (Nitrogen) Uranium series 4.5 billion yrs 244,000 yrs 238 U 234 U 230 Th K-Ar or Ar-Ar 1.3 billion yrs 40 K 40 Ar

Radiocarbon dating: in depth Why is 14 C useful? 1.Production – 14 C is created from 14 N 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 14 C 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 14 7 N n = 14 6 C p

14 C Absorption into carbon-based life: Coral – living & ancient/fossil

Plants, Trees & Charcoal

People & Animals!

A/A 0 = e -λt A – Current amount of 14 C A 0 – Initial amount of 14 C (amount absorbed at time of death) e – Mathematical constant ( …) λ – Constant (ln(2) / half life) t – Time t = 0 t = 1 t = 2 t = 3 t = 4 t = 5 t = 6 Exponential Decay

Measurement of 14 C 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 14 C 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 234 U/ 238 U: –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 –CaCO 3 (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 Artifacts River cobbles Sterile dirt Modern surface

K-Ar datable materials Volcanic ash

Essential Isotope Information: Review Isotope system ½ LifeDate Range from to 14 C5730 yrs50,000 yearsPresent 234 U/ 238 U 234 U/ 230 Th 4.5 billion yrs 244,000 yrs 2 million yrs 450,000 yrs 10,000 yrs present K-Ar1.3 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