Dating
I. Types of dating.
A. Relative Dating - Relative means a date in relation to other things whose date you may or may not know. Involves putting things in typological or stratigraphic sequence. Knowledge of specific events (as in Ice Age) helps confirm dates.
1. Stratigraphy - stratification is the laying down or depositing of strata, one upon the other.
a. Each strata is called a deposit.
b. Stratification implies that a deposit located below another was laid down first.
c. A careful check for disturbance of the site is required.
d. Age of an artifact can sometimes be determined when the deposit in which it was found is dated. This is association.
i. Two objects are said to be found in association means they were buried at the same time.
2. Bone age - A method for determining how old a bone is by examining the amount of nitrogen (decreases over time) in the bone and the amount of fluorine and uranium (which increase) in the bone
a. The most famous use of this technique is in revealing Piltdown forgery 1953).
3. Typological Sequences - A kind of dating based on the idea that objects of particular place and time have a distinctive style and that styles change and develop over time.
a. This was thought of in the 19th century by Montelius, who created a sequence of bronze tools and weapons from Europe.
b. The sequence can then be used to date other objects by matching.
c. Ceramics are commonly classified this way, as are most stone tools.
4. Seriation - deals with assemblages of objects. The objects are assembled into an order which is thought to be analogous of the appearance of each object in time.
a. Contextual seriation - Flinders Petrie first used this to date three tombs for which he found no record of the rulers buried within.
b. Frequency seriation - related to the abundance or lack of a particular thing. For example: rise and fall of popularity of Levis.
5. Linguistic Dating is based on the concept that languages change and develop over time and that the rate of change is calculable. Therefore when we know a specific name we can determine when the name was used, and where. Pantaloons to skivvies.
6. Climate and chronology - Climate changes can be sequenced to produce a relative scale for dating local, regional, or global sites.
a. Pleistocene Chronology (great Ice Ages) - four major glacial advances.
b. Deep-Sea Cores and Ice Cores can be cut as plugs and used to establish seriation.
c. Pollen dating is useful because most plants are climate specific and pollen is nearly indestructible. Core and pollen used on Easter Island.
d. Lichen overgrowth is used to date rock art because lichens grow so slowly and live so long that rate of growth can be equated to calendar years.
7. Faunal Dating relates date sequences with animal occupation ranges.
B. Absolute Dating - is a determination of sequences, sites, and objects in calendar years.
1. Calendars and Historical Chronologies involve corresponding a specific ancient or modern calendar ( Mayan, Gregorian) date with a date on our calendar and reconstructing events and dates forward and backward from there.
2. Annual cycles look at the sequencing created by regularly occurring natural cycles and processes.
a. Glacial-clay deposits called varves are laid down in layer after layer according to the annual freeze and thaw.
b. Dendrochronology uses tree rings to set dates.
i. Years of drought produce thin annular rings, wet years have fat rings.
ii. Each tree forms one ring sequence each year.
iii. Some bristlecone pines are over 4,900 years old.
iv. sections of ring patterns can be matched to give age estimate.
3. Radioactive Clocks - the theory that the rate of decay of radioactive particles occur at a regular, measurable rate.
a. Radio-Carbon dating is the determination of the state of decay of C14, stated, for example, as 3,700 100 B.P. (1950). Requires complex calibration. Good for 250 B.P. to 50,000 B.P.
b. Thermoluminescence dates pottery and other inorganic materials. Pottery is quick heated to 500 C (932 F) and the thermoluminescence created by emission of electrons trapped as uranium, thorium and radioactive potassium atoms decay is measured.
c. Electron-Spin Resonance, Potassium-Argon dating, Uranium-Series dating, Fission-Track dating.
4. Cation-ratio dating determines the age of desert varnish gives dates of 6,400 B.P. Using a number of locations for samples they calibrated the rate of change of cation-ratio of potassium, calcium, and titanium.
5. Archaeomagnetic dating correlates the direction of iron particles in fired clay in permanent installations with magnetic north. As mag. N. changes often, the direction indicates where mag N. was the last time the oven as heated to 650 to 700 F (1202 -1292 F).
6. Chronological correlations bring more than one absolute method of dating together to confirm a single thing.