Absolute dating relative
The carbon-14, along with nonradioactive carbon-13 and carbon-12, is converted to carbon dioxide and assimilated by plants and organisms; when the plant or animal dies, it no longer acquires carbon, and the carbon-14 begins to decay.
The conventional method of measuring the amount of radioactive carbon-14 in a sample involved the detection of individual carbon-14 decay events. This technique involves the direct counting of carbon-14 atoms through the use of the accelerator mass spectrometer and has the advantage of being able to use sample sizes up to 1,000 times smaller than those used by conventional radiocarbon dating.
Furthermore, Egyptian trade wares were used as a basis for establishing the age of the relative chronologies developed for adjoining regions, such as Palestine and Greece.
Thus, Sir Arthur Evans was able to establish an accurate absolute chronology for the ancient civilizations of Crete and Greece through the use of Egyptian trade objects that appeared in his excavations—a technique known as cross-dating.
Since the rate of radioactive decay of any particular isotope is known, the age of a specimen can be computed from the relative proportions of the remaining radioactive material and its decay products.
By this method the age of the earth is estimated to be about 4.5 billion years old.
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.
Each radioactive member of these series has a known, constant decay rate, measured by its half-life , that is unaffected by any physical or chemical changes.All of these techniques have proven somewhat unreliable.Museums sometimes use them to determine if a ceramic is an antique or a modern forgery.When light is used rather than heat to free the accumulated electrons, the technique is known as optically stimulated resonance.
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.
The radioactive carbon-14 method of dating is used to determine the age of organic matter that is several hundred years to approximately 50,000 years old.