Other Dating Methods

LUMINESCENCE

TL - Thermoluminescence
OSL - Optically Stimulated Luminescence

Like ¹⁴C dating, thermoluminescence is related to radioactive decay.

Thermoluminescence is produced by radioactive decay particles (electrons), trapped in mineral grains. Heating the mineral (or exposure to light) releases electrons, and produces a flash of light, setting the clock to 0 (maybe only partial). Thereafter, luminescence accumulation is proportional to age. Used particularly for >50 ka archeological dates.

Dating Range: 1,000 - 300,000,000 yrs

1. measure native TL (OSL)
2. measure sensitivity TL/rad (OSL/rad) (radiation absorbed dose)
3. determine dose rate at site (rad/yr)

ELECTRON-SPIN RESONANCE

1. measure TD Total Dose with spectrometer
2. measure ED External Dose rate in field
3. age (Te) = TD/ED

FISSION TRACK DATING

90 a.m.u & 135 a.m.u particles, 200 MeV

1. etch with acid, count the "native" tracks (microscope 200 - 500 X)
2. heat sample to remove tracks
3. calculate amount of ²³⁸U by irradiating sample with neutron beam to produce artificial fission tracks from ²³⁵U
4. calculate age from native tracks and decay rate of ²³⁸U
   age= #tracks / tracks/yr

Pearlette Volcanic Ash, Yellowstone Park, WY
2.02 +/-0.08 Ma Huckleberry Ridge
1.27 +/-0.1 Ma Mesa Falls
0.616+/-0.008 Ma Lava Creek
Bishop Ash, Long Valley Caldera, CA (near B/M reversal)
0.741+/-0.014 & 0.738+/-0.0006 Ma

AMINO ACID RACEMIZATION & EPIMERIZATION

• if age known, can estimate past temperature
• if past temperature known, can estimate age

• Amino Acids have 2 possible chemical forms
• Only one form (L) produced by living organisms
  L - levorotatory: rotates polarized light left
  D - dextrorotatory to right
• upon death, the 2 forms approach equilibrium
  

• determine proportions of forms of amino acids
• establish rates of equilibration
  a. in laboratory at high temperatures
  b. in field with materials of known age
  
• if past temperature known, establish age
• if age known, estimate past temperature

OBSIDIAN HYDRATION DATING: volcanic glass

obsidian + water = hydrated obsidian (weathering)

greater age = thicker layer of hydrated obsidian


rate is dependent on both temperature and time

clock set to 0 when fresh surface exposed

observe thickness of hydrated layer in thin section
• optical: has different refractive index
• SIMS Secondary ion mass spectrometry
  
establish hydration rate for each type of obsidian by examining pieces of known age, or with high pressure and temperature in lab.

Dating Range: 100 - 1,000,000 yrs

Materials: Indian artifacts, glacial materials, volcanic ash

SURFACE DATING
Cosmogenic Nuclide Exposure Dating

Collision produces spallation products (e.g. neutrons),
which combine to form both stable and unstable products.

Collisions take place at earth's surface  ¹⁴₇N, ¹⁰₅Be, ²⁶₁₃Al, ³⁶₁₇Cl, ³⁹₁₈Ar

eg. 4160 ± 310   ³⁶₁₇Cl atoms yr^-1 mol^{-1 39}K