Dating methods wikipedia
This technique is useful to about 9,000 years ago for samples from the western United States using overlapping tree-ring series from living and dead wood.
The Earth's orbital motions (inclination of the earth's axis on its orbit with respect to the sun, gyroscopic precession of the earth's axis every 26,000 years; free precession every 440 days, precession of earth orbit and orbital variations such as perihelion precession every 19,000 and 23,000 years) leave traces visible in the geological record.
The photons of the emitted light must have higher energies than the excitation photons in order to avoid measurement of ordinary photoluminescence.
A sample in which the mineral grains have all been exposed to sufficient daylight (seconds for quartz; hundreds of seconds for potassium feldspar) can be said to be of zero age; when excited it will not emit any such photons.
The trapped charge accumulates over time at a rate determined by the amount of background radiation at the location where the sample was buried.
Quartz OSL ages can be determined typically from 100 to 350,000 years BP, and can be reliable when suitable methods are used and proper checks are done.Feldspar IRSL techniques have the potential to extend the datable range out to a million years as feldspars typically have significantly higher dose saturation levels than quartz, though issues regarding anomalous fading will need to be dealt with first.The concept of using luminescence dating in archaeological contexts was first suggested in 1953 by Farrington Daniels, Charles A. Saunders, who thought the thermoluminescence response of pottery shards could date the last incidence of heating.Periodically, the magnetic field of the earth reverses leaving a magnetic signal in volcanic and sedimentary rocks.This signal can be detected and sequences recorded, and in the case of volcanic rocks, tied to radiometric dates.
Because these can be calibrated reliably over a period of 40 million years this provides an alternate verification to radiometric dating in cases where sufficient record exists to provide a reliable trace.