Carbon dating is not an app for old people wanting to hook up

The rocks and the land tell far longer stories than humans.

Peter Miles
Feb 28 · 5 min read
Rock pool and waterfall, Ingalalla Falls, South Australia. Image by author.

Australian Aboriginal people have inhabited the Australian continent for a very long time. They are the longest human civilization and have looked after the country far better than we are now. Aboriginal people have great reverence and respect for and indeed some fear of their Ancestors, and using the latest dating techniques of archeological remains, some of those Ancestors may be more than 60,000 years old.

Back in the present day, Aboriginal artifacts have been found in archeological diggings at rock escarpment shelters, and river and coastal settlement sites which have long been repeatedly and often continuously inhabited. These artifacts range from large stone tools, to finely worked stone and bone implements and spear points, to clay used for rock painting. They demonstrate the evolution and development of Aboriginal culture over as much as three epochs of geological deep time, the Pleistocene when Homo sapiens left Africa, the Holocene the most recent interglacial period, and the current Anthropocene beginning with the European Industrial Revolution.

Various dating techniques are used to determine the age of these artifacts and hence the time of occupation of the land. Radiocarbon dating, optically stimulated luminescence and thermoluminescence dating are three methods that have been used.

Rock escarpment, South Australia. Image by author.

Radiocarbon dating resulted from work on carbon isotopes as part of the 1940s Manhattan Project. Radiocarbon dating requires carbon which is a fundamental part of life. When an organism is alive carbon moves in and out of its body until it dies, then carbon movement stops. At this point the carbon 14 isotope starts to decay. Radiocarbon measures this rate of decay against the stable isotope carbon 12. The rate of decay and amount of carbon 14 can give a date, a time of death of the organism (Griffiths, 2018).

Carbon decays quickly with approximately half the carbon 14 gone after 5,700 years and about 1% left after 38,000 years. The amount of atmospheric carbon varies from year to year and this needs to be calibrated when calculating the number of years of age, this is done with previously worked out tables but is the reason why some dates vary. Added to the difficulty is carbon can be easily contaminated with carbon from other sources, eg from hands or organic matter (Aitken, 2014).

Radiocarbon dating time limit was 40,000 years at best, even with new developments such as Accelerator Mass Spectrometry using magnetics to measure carbon atoms, and Acid Base Oxidation acid to remove very thin layers of contamination, the technical limit is 50,000 years BP, Before Present (Tuniz, Gillespie & Jones, 2009).

BP, Before Present, with Present deemed to be the 1st January 1950. This date has been selected by scientists as a convenient date to remember just before large-scale atmospheric testing on nuclear weapons which has altered the carbon ions ratio.

Thermoluminescence dating, dates quartz sand from the last time it was exposed to sunlight. When a grain of quartz is buried and therefore protected from sunlight, it starts to absorb background radioactivity from the surrounding sediment, with electrons from the radioactivity building up a charge in the crystalline lattice of the quartz. When the grain of sand is exposed to light, as in optically stimulated luminescence, or heat as in thermoluminescence, the built-up charge is released and glows or luminesces. The intensity of the glows is greater with more electrons and greater age (Griffiths, 2018).

Radiometric dating measures the decay of radioactive isotopes, often using Potassium 40 decaying to Argon 40 which has a half-life, time for half the atoms to decay, of 1.25 billion years. This method is used to measure the far longer ages of minerals, rocks and fossils (Knox et al., 2014).

A most important site and discovery of the great age of Australian Aboriginal culture was at Devil’s Lair, south of Perth, Western Australia. In the 1970s a 5-metre-deep trench was excavated in the Devil’s Lair cave, with gradually deeper and older blackened bones, fire hearths, shells and stone artefacts, with the oldest around 38,000 Years BP. This was also the limit of the radiocarbon dating ability at the time (Dortch & Dortch, 1996).

A sandstone rock shelter in Kakadu, Northern Territory, named Madjedbebe, has been excavated in the past with a 4.5m deep square shaft size pit dug. The artefacts found were dated in 2017 using the luminescence technique with the lowest artefacts dated at 65,000 YBP (Clarkson, et al., 2017) giving the oldest carbon date so far that we can measure.

This date gave scientific support to the Australian Aboriginal People’s sacred beliefs, to what they had known all along, that their Ancestors had been here for a very long time. 65,000 years can be measured but is very hard to imagine. To a people who have been physically and culturally displaced by European settlers, radiocarbon and thermoluminescence dating and the archeologists who have painstakingly determined the great ages involved, have been a great emotional help to them and all indigenous peoples, who are trying to retain their culture while they now have to live in two worlds.

Ancient Indigenous Rock Art, Kakadu, Northern Territory. Image — Flickr Creative Commons.

References:

Aitken, M. J. (2014). Science-based dating in archaeology. Routledge.

Clarkson, C., Jacobs, Z., Marwick, B., Fullagar, R., Wallis, L., Smith, M., … & Pardoe, C. (2017). Human occupation of northern Australia by 65,000 years ago. Nature, 547(7663), 306–310.

Dortch, C. E., & Dortch, J. (1996). Review of Devil’s Lair artefact classification and radiocarbon chronology. Australian Archaeology, 43(1), 28–32.

Griffiths B. (2018) Deep Time Dreaming (1sted.). Victoria, Australia.: Black Inc. Book.

Knox, B., Ladiges, P., Evans, B., Saint, R., (2014). Biology: An Australian Focus (5th Ed.). NSW. Australia.: McGraw-Hill Education. Book.

Tuniz, C., Gillespie, R., & Jones, C. (2009). The bone readers: atoms, genes and the politics of Australia’s deep past.

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Peter Miles

Written by

Peter Miles B.Env.Sc. 45 years in Environmental Science, specializing in Wildlife and Conservation Biology. Writes about Animals, Revegetation & Climate Change.

Age of Awareness

Stories providing creative, innovative, and sustainable changes to the ways we learn

Peter Miles

Written by

Peter Miles B.Env.Sc. 45 years in Environmental Science, specializing in Wildlife and Conservation Biology. Writes about Animals, Revegetation & Climate Change.

Age of Awareness

Stories providing creative, innovative, and sustainable changes to the ways we learn

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