Describe process absolute dating
Absolute dating can be achieved through the use of historical records and through the analysis of biological and geological patterns resulting from annual climatic variations, such as tree rings (dendrochronology) and varve analysis.After 1950, the physical sciences contributed a number of absolute dating techniques that had a revolutionary effect on archaeology and geology.
Yet another technique measures the quantity of trapped electrons by detecting the amount of microwave radiation they absorb (electron-spin resonance); it has the advantage that it can be utilized several times on a given sample.By counting each pair of varves the age of the deposit can be determined.The absolute dating methods most widely used and accepted are based on the natural radioactivity of certain minerals found in rocks.Thus it is possible to measure the time that has elapsed since the material solidified.Thermoluminescence, used in dating archaeological material such as pottery, is based on the luminescence produced when a solid is heated; that is, electrons freed during radioactive decay and trapped in the crystal lattice are released by heating, resulting in luminescence.The varved-clay method is applied with fair accuracy on deposits up to 12,000 years old.
Streams flowing into still bodies commonly deposit layers (varves) of summer silt and winter clay through the year.
The accelerator mass spectrometer technique reduces the amount of statistical error involved in the process of counting carbon-14 ions and therefore produces dates that have smaller standard errors than the conventional method.
Paleomagnetic dating is based on changes in the orientation and intensity of the earth's magnetic field that have occurred over time.
Those laid down during the fall and winter have a dark color because of the presence of dead vegetation; those deposited during the rest of the year have a light color.
The stratigraphy may also reflect seasonal variation in the velocity of stream flow.
In dendrochronology, the age of wood can be determined through the counting of the number of annual rings in its cross section.