Relative, Historical & Absolute dating
What is Realtive dating?
It is the use of techniques which identify the order in which sites or artefacts were used in a sequence from earliest to latest.
What is Absolute dating?
The use of dating techniques that try to establish an exact or approximate calendar date for a site or artefact.
What is Historical dating?
For sites less than 5000 years old there maybe evidence which can provide precise dates as long as the orginal language is used.
Two examples of evidence used in historical dating:
Coins (usually roman coins as they have a picture of the emperor at the time on them therefore we know that it could have been made or dropped before that time) & inscriptions.
What does Terminus post quem mean?
The earliest possible date for an archaeological deposit
What does terminus ante quem mean?
The lastest possible date for an archaeological deposit.
What is an assemblage? successive groups of contemopry artefacts which are commonly found together.
What is seriation? A sophisticated statistical technique to find out and plot patterns of artefacts found.
How does seriation work? The relative proportions of pottery types at a new site would be compared with the seriation chart to give it an approximate date.
What are the main limitations of seriation and relative dating?
1. They can only be used to give calendar dates
2. Radiocarbon dating showed that achaeologists have underestimated timespans in prehistory
3. One type of artefact doesn't always succed another.
What is Obsidian? A volcanic glass that can be worked to provide razor-sharp cutting edges
Where was flint used to perform the same function? Northern europe
What happens to obsidian as soon as it is broken? It begins to absorbe water from the atmosphere at a known rate
How can this be used for dating? By measuring how deep the water has penetrated into the obsidian on one site it can be compared to others
What is the limitation of Obsidian Hydration? Not accurate as speed of hydration varies with local temperatures
What is dendrochronology? Tree ring dating
How far back does dendrochronolgical sequence go in Europe? 11,000 years
What are the limitations of dendrchronology?
1.Carpenders discard the soft sapwood under the bark - which is important and can contain up to 50 rings
2. Not all areas have sufficently varied seasons or enough surving timber to constuct a sequence
3. Around 50 years of tree rings are needed to effectivly date timber
What time periods is dendrochronolgy particularly useful for? Neolithic onwards
How much C-14 do all living things absorb? 1%
What is different about the C-14 carbon isotope to other carbon isotopes? It decays where as other carbon isotopes don't.
How long does C-14 take to decay by half? 5730 years
How can this rate of decay by used for absolute dating? Its compared to ther organic samples of carbon isotopes
What 2 problems have been identified with C-14 dating?
1. The orginal half-life was shown to be too little
2. The amount of carbon in the atmosphere varies
How accurate is C-14 Dating? 68% its within the date indicated and 95% its within twice the date indicated
Radiocarbon dating cont.
What is C-14 used to date? Organic materials e.g. bone, shell and plant remains
What is C-14 unsuitable to date? Cremated bone
What are the suitable time periods for C-14 dating? 40,000 years
What can be measured? The number of years since the pottery was fired
How can age be determined? The electrical change released as light into the item the more light the longer its been since the clock setting event
What is actually dated? the age of the pottery
What time period is it useful for? from present to 400,000 years ago
What are the two limitations of TL?
1. Not accurate, compared to C-14 dating
2. Can give false readings due to radiation
What does OSL measure? The time since sediments were last exposed to sunlight or in the case of ceramics when they were last heated to over 400 oC