Absolute dating relative
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.
In dendrochronology, the age of wood can be determined through the counting of the number of annual rings in its cross section.
Tree ring growth reflects the rainfall conditions that prevailed during the years of the tree's life.
Paleomagnetic dating is based on changes in the orientation and intensity of the earth's magnetic field that have occurred over time.Each decay element has an effective age range, including uranium-238 (100 million to 4.5 billion years) and potassium-40 (100,000 to 4.5 billion years).Other methods that depend on the effects of radioactive decay include fission track dating and thermoluminescence.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.
By matching the tree rings on an archaeological sample to the master sequence of tree ring patterns, the absolute age of a sample is established.