Archaeologists are basically detectives who attempt to reconstruct past human activities from evidence most of which is buried in the earth. Archaeology involves experts from many other fields. Even the science of archaeology, commonly divided into prehistoric and historical can be further divided into various fields: paleolithic, Egyptology, classical, industrial, environmental, underwater, salvage, and experimental to name a few. Archaeologists rely on two principal techniques or methods of dating artifacts and sites: relative and absolute dating.
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Relative and Absolute Dating Techniques
Before the twentieth century, archaeologist were confined to the use of relative dating techniques. These involved speculation, estimations and educated guesswork. While many of these methods are still used today, more precise and definite dating occurs using absolute dating techniques. The latter increase in number and precision with advances in science and technology.
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Common Relative Dating Techniques
Relative dating techniques are useful in establishing the relative age of artifacts, fossils, and sites. They are not used or able to pin-point ages and dates of material but to compare findings from one site to another.
- Involves comparing information from one geological or archaeological profile to another (correlation)
- Relies on “law of superposition”: artifacts found in strata at the bottom of a site are older than those found above
- Based on the fact that the amount of fluorine in bones is proportional to their age
- Oldest bones contain most fluorine
- Accuracy varies since rate of fluorine formation is not constant
- Involves microscopic examination of (fossil) pollen grains in stratified peat and lake deposits
- The kind of pollen in a geological strata can be connected to the type of vegetation in that area at a certain time
Common Absolute Dating Techniques
Absolute dating techniques are more precise and provide greater accuracy in dating ages of archaeological evidence.
- Technique based on number of rings of growth found in tree trunks
- Comparison of trunks to artifact (eg. Beam in a house) helps to date the artefact
- Reliable for dating sites between approximately 6,000 and 11,000 years.
Radio-Carbon Dating (Carbon 14/C-14)
- Technique relies on measurement of amount of radioactive carbon (C-14) which has disintegrated since death of organic materials at archaeological sites
- fairly accurate because radioactive carbon breaks down at a fixed rate; half life of approximately 5730 years
- Reliable for dating materials as old as 50,000 years but accuracy can be affected by environmental variables
Potassium-Argon Analysis (K-Ar)
- Test is NOT performed on artefact/fossil but on surrounding material
- Technique measures ratio of radio potassium to argon in volcanic debris surrounding fossil/artefact
- (following intense heating) radioactive potassium decays to form argon at a known rate
- Unlike C-14 dating, K-Ar method measures accumulation of elements not their disappearance
- Reliable for dating fossils millions of years old
Amino Acid Racemization
- Technique measures ratio of D-amino acids to L-amino acids
- After death, certain amino acids present in bone, teeth, and shells change
- Ratio of L-amino acids to D-amino acids increases with time and age
- Accuracy can be affected by local differences in temperature and amount of water in ground
- Findings must be corroborated by other tests
- Used to date materials from between 5,000 and 100,000 years old