Absolute dating relative
All of these techniques have proven somewhat unreliable.
Museums sometimes use them to determine if a ceramic is an antique or a modern forgery.
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.
Other methods that depend on the effects of radioactive decay include fission track dating and thermoluminescence.These techniques are based upon the measurement of radioactive processes (radiocarbon; potassium-argon, uranium-lead, uranium-thorium, thorium-lead, etc.; fission track; thermoluminescence; optically stimulated luminescence; and electron-spin resonance), chemical processes (amino-acid racemization and obsidian hydration), and the magnetic properties of igneous material, baked clay, and sedimentary deposits (paleomagnetism).Other techniques are occasionally useful, for example, historical or iconographic references to datable astronomical events such as solar eclipses (archaeoastronomy).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.
Because rainfall patterns vary annually, any given set of tree ring patterns in a region will form a relatively distinct pattern, identifiable with a particular set of years.