What is OSL?

Optically stimulated luminescence (OSL) dating is a radiometric/trapped charge method that produces absolute ages.Luminescence dating measures the amount of electrons that have accumulated in defects (known as traps) in the crystal lattice of certain minerals (quartz and potassium feldspar). Electrons accumulate at a predictable rate in these buried crystals/grains, as a result of exposure to ionising radiation from their immediate surroundings; almost like a battery recharging. When exposed to heat or daylight electrons that have accumulated in the “battery” discharge releasing a measurable flash of light. Traditionally OSL has been applied to sand sized grains in sediments or ceramics, but more recently a new method has emerged called Rock Surface Burial Luminescence Dating.

Application in FROM STONE TO HOME

For FROM STONE TO HOME, OSL and Rock Surface Burial Luminescence Dating will be used to acquire absolute ages from sediments and rocks collected at potential quarry sites across the Aegean that are thought to be the sources of Neolithic polished stone tools found at excavations and in museums across the world.

Challenges and Solutions

Dating of human activity is mostly associative when no or only poor quality organic remains are present. This methodology routinely relies upon artefact typology, coins or the architecture of nearby dwellings.In contrast to associated dating, conventional OSL using sediments has a long established track record of producing absolute ages, it can deliver highly reproducible results, and quartz and feldspar grains are ubiquitous in almost every environment. Additional advantages include: there are no special requirements for preservation, it has a very dynamic age range of 10 years to ~500 ka (compared to ¹⁴C ˂ 40 ka), and no calibration sample is required (¹⁴C dating requires this). However, chemical processing is quite aggressive and this leads to the loss of material; also, once measured, grains are difficult to recover. Additionally, in some countries quartz has no OSL signal (this is a common issue in Greece), and it can be time consuming establishing whether the luminescence signal in sediments was fully reset prior to final deposition. Using luminescence to date buried rock surfaces overcomes the issue of poor luminescence characteristics in sediments from Greece, the process of establishing complete signal resetting in a rock sample is much simpler, and no chemical treatment is required. Most significantly, very little organic material has been found during the field surveys in Greece meaning that luminescence dating has become the primary option for obtaining precision ages from these important quarrying sites.

Outcome

The rock surface burial luminescence method can directly date when rocks were moved or modified by human activity. Used in conjunction with standard OSL dating it should be possible to establish a robust chronology for quarrying activity associated with polished stone tool production and distribution in the Aegean Neolithic.