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A new era in scientific dating.
Luminescence dating is a method used to determine how long archaeological materials, landforms, and sediments have been buried after being exposed to sunlight or heat. It can be applied to samples as young as a few decades and as old as several hundred thousand years.
What is luminescence dating?
Luminescence dating broadly refers to a series of techniques that exploit the luminescence properties of minerals (typically quartz) to determine how long they have been buried in the natural environment or within archaeological sites.
When minerals are buried, they are exposed to cosmic rays from outer space that penetrate the ground surface, as well as natural ambient ionizing radiation that is emitted from the surrounding sediments. Some of the energy derived from this radiation becomes stored within the minerals, and if these minerals are later exposed to light or heat, the stored energy is released in the form of light (i.e., luminescence).
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Samples for luminescence dating are collected from archaeological sites or landforms in complete darkness (often using opaque sample tubes or black bags), taken to a light-safe laboratory, prepared to isolate the targeted minerals, then stimulated with heat or light sources to release their stored energy.
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The brightness of the resulting luminescence is measured and used to calculate the total amount of radiation the minerals had been exposed to during their period of burial in the environment (also known as the absorbed dose and measured in units of Gray).
To obtain an age, this value is divided by the amount of radiation that the sample receives from its environment in a year (i.e., the dose rate measured in units of Gray per year).
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The total radiation the minerals were exposed to during burial (Gray)
The amount of radiation the minerals receive in a year (Gray per year)
When is Luminescence dating needed?
Scientists rely on luminescence dating to help answer many questions regarding Earth and human history, and will collect samples for a number of reasons. These include:
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To determine the age of landforms or sedimentary deposits and associated materials such as artefacts
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To validate existing geochronological data or expected ages of a site
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To date sites that are older than the upper limit of radiocarbon dating (~55,000 years) or where organic matter is not available
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To date materials (cookware or hearths) that have been heated in the past
Sample Collection Process
Samples for luminescence dating can be collected in many ways and can include different types of material.
Materials most commonly dated are grains of sand or silt, however rock surfaces, pottery, rock art, and even archaeological constructions, such as walls and buildings have also been sampled.
Because luminescence dating methods determine the last time a mineral has been exposed to light or heat, it is imperative that light or heat does not contaminate the luminescence sample during the sampling process. Before sampling, we recommend watching the tutorial videos in our learning hub.
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To obtain an age for a sedimentary unit or artefact of interest, two types of sample must be collected: i) a sample for luminescence measurements, and ii) one or more samples for the measurement of dose rate.
In order to obtain an accurate age, details about your site and sample must be recorded and provided to Vicus upon sample submission.
Guidelines and tutorial videos for sample collection and required site information can be found at our learning hub.
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Applications of luminescence dating
Insights into human history and evolution
Luminescence ages from ancient sites can help us reconstruct our history through time and space. It has been particularly important for helping us resolve the details of our behaviour, movements, and resilience to environmental change before ~55,000 years ago (the upper limit of radiocarbon dating). Luminescence ages have helped us better understand when we first entered Australia and the Americas, and have helped establish our relationship with our ancestors and relatives in the human family tree (e.g., Homo Erectus, Neanderthals, Homo Floresiensis and the Denisovans).
Sensitivity of coastal regions to tsunamis, storms, and sea level change
In order to better understand the sensitivity of heavily populated coasts to global environmental change, we need a detailed chronology of past events. Luminescence ages can help determine when coastal deposits (beaches, beach ridges, foredunes, paleosols, etc.) formed, which, in turn, can fill gaps in our knowledge of past changes in relative sea level. Likewise, chronologies for ancient coastal storms and tsunami events can help identify present and future risks to coastal areas.
The history of aridity and drought
Knowledge of the extent and timing of droughts in the past is imperative for understanding the potential impacts of drought in the future. Some of the easiest samples to date come from wind transported material (e.g., dune sand and loess), which has experienced maximal sun exposure prior to burial. Luminescence ages from windblown deposits have the potential to constrain the timing of stabilisation of dormant dunes and periods of aridity or drought in the geological record. These ages are also critical for reconstructing environmental change in deserts where organic matter for radiocarbon dating is sparse or absent.
Paleolakes and paleofloods
Luminescence ages from lake deposits and landforms can provide important chronologies for climate-induced lake level fluctuations and floods. For example, luminescence dating has played a key role in establishing the history of expansion and contraction of ancient megalakes that once occupied Australia’s interior. These lakes would have served as a major water source for Australia’s earliest inhabitants, and their disappearance may have played a role in the extinction of Australia’s megafauna.
River system dynamics
River valleys are important water sources for people and animals and have served as valuable sites for early inhabitants. River planforms, bedloads, and rates of incision and deposition are linked to climate, local tectonics, channel form history, sediment supply, and, in areas close to the coast, changes in relative sea level. Luminescence ages provide valuable chronologies for landscape changes recorded by (and triggered by) rivers. Such research into past flood events and changes in channel morphology can inform policy makers and developers about risks and hazards associated with rivers.
The timing of tectonics
Luminescence dating has proven useful in determining fault slip rates and the timing of earthquakes and tectonic (or seismic) movements. Dating seismic events often involves dating landslides or tsunami events triggered by earthquakes, or dating landforms and sediments that have been displaced by faults.
Illuminating insights from luminescence dating
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The earliest evidence of people in Australia
Luminescence dating was used to establish a new minimum age for the arrival of people in Australia. Grinding stones, ground ochres, reflective additives, and ground-edge hatchet heads excavated at the Madjedbebe rock shelter in northern Australia suggested that people have made Australia their home since at least 65,000 years ago.
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The earliest evidence of people in the Americas
Ancient footprints preserved at White Sands National Park, New Mexico, have been dated using luminescence and radiocarbon techniques to the last ice age, ~21,000-23,000 years ago. The interpretation of the geochronology has since been in dispute, however, if these results are confirmed, they will be the earliest evidence of the arrival of people in the America’s.
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What (or who) killed Australia’s megafauna?
Megafauna are large animals that roamed the Earth during the Pleistocene, 2.5 million to 11,700 years ago. Australian megafauna, including the huge wombat-shaped Diprotodon and giant goanna Megalania, mysteriously went extinct around the time people arrived. Luminescence ages are used to constrain the age of these ancient creatures as well as the timing of their extinction. Recent compilations of luminescence ages, radiocarbon ages, and other data suggest that climate was not the main driver of megafauna extinction, but rather people.
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The history of Australia’s megalakes
Lakes Frome, Callabonna, Blanche, and Gregory form an arc of playa lakes around the northern Flinders Ranges, Australia. Luminescence dating of ancient paleo shorelines has shown that during the Pleistocene, all four of these lakes expanded and combined to form a megalake that is now called Lake Mega-Frome. When Lake Mega-Frome spilled into the neighbouring Lake Eyre system (Mega-Eyre), these combined to form Australia’s largest paleolake system that persisted as recently as 50-47,000 years ago. The subsequent drop in the level of Lake Mega-Frome represents a major climate shift toward aridity that coincided with the arrival of humans and the demise of the megafauna.
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Australia’s desert dunes were most active during the Ice Age
Counterintuitively, ages of dunes from Australia’s hinterland show that they were most active when the climate was cold, rather than hot. Luminescence ages from these dunes show peak activity during what we call the “Last Glacial Maximum”, or the height of the last Ice Age ~21,000 years ago.
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The most common minerals on Earth’s surface
Luminescence dating techniques have been developed for two main minerals, quartz and feldspar. It’s a good thing too, because these minerals happen to be the most abundant minerals on the surface of the Earth. Quartz, aka SiO2, makes up about 12% of the land surface and about 20% of the Earth's crust. Feldspar makes up ~60% of the Earth’s crust. The term feldspar is used to describe any mineral that consists of framework aluminum (Al), oxygen (O) and silicon (Si) atoms plus an additive.
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Australia shines brighter
The accuracy of a luminescence age partly depends on the brightness of the measured luminescence signal, which depends on how the measured mineral formed and how long it has been mobile on the Earth’s surface. Australian quartz produces some of the brightest luminescence signals in the world, making it a prime location for the most accurate luminescence ages.