Last updated: February 2, 2026
A method that dates when sediment was last exposed to sunlight.
OSL dating1 measures when sand or dirt was last exposed to sunlight. Scientists use it to date when sediments were buried.
The method is based on how natural radiation affects crystals over time.
The Basic Process
Step 1: Natural background radiation (from uranium, thorium, potassium in soil) constantly hits quartz crystals, trapping electrons in tiny defects within the crystal structure.
Step 2: Sunlight or heat releases these trapped electrons, "resetting" the crystal to zero.
Step 3: After burial (no more sunlight), radiation continues hitting the crystals, building up trapped electrons again.
Step 4: In the lab, scientists shine light on the crystals, releasing the trapped electrons as light (luminescence). More trapped electrons = more light = longer burial time.
Samples must be collected in complete darkness (using opaque tubes or working at night) to avoid accidentally resetting the signal.
Under red light only, scientists separate and clean the quartz/feldspar crystals using acids and sorting by size.
Crystals are stimulated with light in a special reader. The amount of light they emit indicates the "equivalent dose" (De).
Scientists measure uranium, thorium, and potassium levels in the surrounding sediment to calculate the "dose rate" (Dr).
Age = Equivalent Dose (De) / Dose Rate (Dr)
- Equivalent Dose (De): Amount of radiation the crystal absorbed since burial (measured in Grays)
- Dose Rate (Dr): Rate of radiation exposure per year (Grays per 1,000 years)
If a quartz crystal shows an equivalent dose of 50 Grays, and the dose rate is 2 Grays per 1,000 years, then: 50 / 2 = 25,000 years.
Dating glacier deposits, river terraces, sand dunes, lake sediments, and volcanic ash layers.
Determining when sediments at archaeological sites were deposited, providing age constraints for human occupation.
Dating when sediments were disturbed by ancient earthquakes.
Occasionally used to determine when materials were last exposed to light in legal investigations.
Scientists acknowledge several significant limitations:
If crystals weren't fully exposed to sunlight before burial, they retain some signal from earlier exposure, making ages appear older than they actually are.
Not all quartz and feldspar crystals work well for dating. Some don't store electrons properly or give unstable signals.
Calculating dose rates requires accurate measurements of uranium, thorium, and potassium levels, plus accounting for water content and cosmic radiation. Changes over time can significantly affect results.
Feldspar signals can fade over time (giving ages that are too young), while high radiation doses can saturate the traps (limiting how old samples can be dated).
Burrowing animals, plant roots, and other disturbances can mix crystals of different ages, complicating age interpretation.
Modern OSL uses sophisticated protocols developed by researchers like Murray & Wintle (2000)2 and refined in Murray & Wintle (2003)3. The technique originated with Huntley et al. (1985)4.
Scientists claim these methods include built-in accuracy tests such as recycling ratios, dose-recovery tests, and thermal stability checks to identify problems with sensitivity changes and instrument drift.
Researchers claim OSL ages match other dating methods when they can be compared, including radiocarbon dating, volcanic ash dating, and geological layering patterns. They point to examples like:
Studies using OSL dating have reported very old ages:
Young Earth Creationists point to several significant issues with OSL dating:
OSL dating assumes radiation levels have been constant over time. However, if radiation levels were significantly higher in the past (due to different atmospheric conditions, cosmic ray exposure, or decay of short-lived isotopes), this would dramatically compress the apparent time scale. A 5-15 times increase in dose rates could compress claimed ages of 50,000-150,000 years into less than 10,000 years.
Even with single-grain analysis, there's no way to guarantee that all crystals were completely reset before burial. Systematic incomplete resetting across multiple samples could consistently inflate ages.
The fact that multiple independent labs and different techniques consistently give old ages doesn't necessarily indicate accuracy--it could reflect systematic problems in the underlying assumptions or calibration methods used across the field.
Many of the "independent" verification methods (like other radiometric dating techniques) rely on similar assumptions about constant decay rates and initial conditions, making the verification somewhat circular.