Absolute dating

Some scientists prefer the terms chronometric or calendar dating, as use of the word "absolute" implies an unwarranted certainty of accuracy.

Particular isotopes are suitable for different applications due to the types of atoms present in the mineral or other material and its approximate age.

Cosmic radiation entering Earth's atmosphere produces carbon-14, and plants take in carbon-14 as they fix carbon dioxide.

Potassium is common in rocks and minerals, allowing many samples of geochronological or archeological interest to be dated.

Argon, a noble gas, is not commonly incorporated into such samples except when produced in situ through radioactive decay.

The date measured reveals the last time that the object was heated past the closure temperature at which the trapped argon can escape the lattice.

Heating an item to 500 degrees Celsius or higher releases the trapped electrons, producing light.

Optically stimulated luminescence (OSL) dating constrains the time at which sediment was last exposed to light.

Upon burial, the sediment accumulates a luminescence signal as natural ambient radiation gradually ionises the mineral grains.

Careful sampling under dark conditions allows the sediment to be exposed to artificial light in the laboratory which releases the OSL signal.

Dendrochronology can date the time at which tree rings were formed, in many types of wood, to the exact calendar year.

Dendrochronology has three main areas of application: paleoecology, where it is used to determine certain aspects of past ecologies (most prominently climate); archaeology, where it is used to date old buildings, etc.

When an organism dies, control over the configuration of the amino acids ceases, and the ratio of D to L moves from a value near 0 towards an equilibrium value near 1, a process called racemization.