Teacher background information


Year 9 Science Content Description

Science Understanding

Chemical sciences

All matter is made of atoms that are composed of protons, neutrons and electrons; natural radioactivity arises from the decay of nuclei in atoms (ACSSU177 - Scootle )

  • investigating how radiocarbon and other dating methods have been used to establish that Aboriginal Peoples have been present on the Australian continent for more than 60,000 years (OI.6)

This elaboration provides students with a context for consolidating their understanding of the structure of atoms, and how natural changes in the nuclei of atoms of some elements allow materials to be dated. Students learn how methods based on the phenomenon of radioactivity, in conjunction with other, more recently developed dating methods, have allowed archaeologists to confirm what First Peoples have long held to be true: that Aboriginal people have been present on the Australian continent for more than 60,000 years.

Elements are made up of atoms. Atoms are made up of smaller particles called protons, neutrons and electrons. The atoms of each element contain the same number of protons in their nuclei. The number of neutrons in these atoms may, however, vary. Atoms of the same element, but with different numbers of neutrons are called isotopes. The element carbon, for example, exists naturally as three different isotopes: carbon-12, carbon-13 and carbon-14, generally denoted in the form of their chemical symbols 12C13C and 14CAll of these atoms contain 6 protons – this is what makes them carbon atoms. The number of neutrons in each of these isotopes is 6, 7 and 8 respectively. Some isotopes, such as 14C, are unstable. In a process called radioactive decay, the composition of their nuclei changes to become more stable nuclei. The rate at which this decay occurs differs for each particular radio-isotope. In the case of 14C, the rate of decay is such that half of the 14C nuclei in any given sample will decay in 5,730 years. This duration is called the half-life of 14C. 

Carbon-14 atoms are formed in the Earth’s upper atmosphere by the interaction of cosmic ray neutrons with nitrogen-14 atoms (14N). The 14C atoms combine with oxygen to form carbon dioxide which then enters the biosphere primarily via photosynthesis. While an organism is alive the ratio of 14C : 12C isotopes in its body is similar to that in the atmosphere and remains relatively constant. When the organism dies, there is no further uptake of 14C, so the ratio of 14C : 12C changes as the 14C atoms radioactively decay to form 14N again. Therefore, by measuring the 14C : 12C ratio in biological artefacts, it is possible to calculate the amount of time that has passed since the organism died. Since the half-life of 14C is 5,730 years, this method can be used to measure dates up to about 40,000 years in the past with reasonable accuracy. 

Radiocarbon dating procedures have been used by archaeologists to study the migration patterns of early humans and the antiquity of the habitation of the Australian continent by Aboriginal Australians. While people of European descent have been living in Australia for a little over 200 years, in the first half of the 20th century it was generally accepted by the scientific community that Aboriginal peoples have been living in Australia continuously for about 20,000 years. The discovery of human remains at Lake Mungo in western New South Wales, however, lengthened this timeline. These remains, informally referred to as ‘Mungo Lady’ and ‘Mungo Man’, were unearthed in 1969 and 1974 respectively. The original radiocarbon dating of Mungo Lady’s remains revealed that they may have been as old as 26,500 years. Mungo Man’s remains were estimated, using stratigraphic comparison with Mungo Lady, to being between 28,000 and 32,000 years old. In 2003, a panel of experts using a range of more refined dating techniques agreed that the Lake Mungo remains are probably about 40,000 years old.  

Based on recent archaeological evidence, it is now clear that the Australian Aboriginal peoples have occupied the Australian continent for even longer than the Lake Mungo calculations suggested. 

Analysis of excavations at the Madjedebe or Malakunanja II rock shelter in Arnhem Land using a combination of radiocarbon dating and other methods based on thermal and optical luminescence has revealed evidence of continuous habitation of Australia by Aboriginal peoples for at least 65,000 years. 

This elaboration provides opportunities for students to investigate the advantages and disadvantages of a range of dating techniques, in particular, the complications associated with radiocarbon dating. Investigation could take into account the fact that the 14C : 12C ratio in the atmosphere has not always been constant, or the impact of contamination by ‘younger’ carbon on the age determination, and the methods scientists are using to minimise these limitations. 

Furthermore, students will have an opportunity to investigate competing viewpoints about the spread of people to Australia and gain an appreciation of the vast timescale of Aboriginal habitation on the Australian continent. 

When exploring this elaboration, it is crucial to keep the following points in mind:

·        interfering with the ancestral remains discovered at Lake Mungo is a sensitive issue for the Ngiyampaa, the Mutthi Mutthi and the Paakantji Aboriginal people who are descendants of Mungo Lady and Mungo Man and custodians of the remains

·        in many cases, Aboriginal peoples’ view on how long they have lived in Australia, embodied in the Dreaming and Aboriginal Law, is that they have always lived in Australia.



In the construction of this teacher background information, a list of consulted works has been generated. The consulted works are provided as evidence of the research undertaken to inform the development of the teacher background information. To access this information, please read and acknowledge the following important information:

Please note that some of the sources listed in the consulted works may contain material that is considered culturally offensive or inappropriate. The consulted works are not provided or recommended as classroom resources.

I have read and confirm my awareness that the consulted works may contain offensive material and are not provided or recommended by ACARA as classroom resources.

The following sources were consulted in the construction of this teacher background information. They are provided as evidence of the research undertaken to inform the development of the teacher background information. It is important that educators recognise that despite written records being incredibly useful, they can also be problematic as they are often based on non-Indigenous interpretations of observations and records of First Nations Peoples’ behaviours, actions, comments and traditions. Such interpretations privilege western paradigms of non-First Nations authors and include, at times, attitudes and language of the past. These sources often lack the viewpoints of the people they discuss and can contain ideas based on outdated scientific theories. Furthermore, although the sources are in the public domain, they may contain cultural breaches and cause offence to the Peoples concerned. With careful selection, evaluation and community consultation, the consulted works may provide teachers with further support and reference materials that could be culturally audited, refined and adapted to construct culturally appropriate teaching and learning materials. The ability to select and evaluate appropriate resources is an essential cultural capability skill for educators.

American Chemical Society. (2016). National historic chemical landmarks: Discovery of radiocarbon dating. Retrieved from https://www.acs.org/content/acs/en/education/whatischemistry/landmarks/radiocarbon-dating.html

Australia's Nuclear Science and Technology Organisation. (2016, December 6). Development of new techniques makes it possible to date Australian Aboriginal rock art. ANSTO News. Retrieved from http://www.ansto.gov.au/AboutANSTO/MediaCentre/News/ACS112993

Bednarik, R. G. (2002a). The dating of rock art: A critique. Journal of Archaeological Science, 29(11), 1213-1233.

Bednarik, R. G. (2002b). Radiocarbon analysis of inclusions in accretions. Retrieved from http://www.ifrao.com/radiocarbon-analysis-of-inclusions-in-accretions/

Bednarik, R. G. (2002c). Radiocarbon analysis of mineral accretions. Retrieved from http://www.ifrao.com/radiocarbon-analysis-of-mineral-accretions/

Cane, S. (2013). First footprints: The epic story of the First Australians. Sydney: Allen & Unwin.

Daley, P. (2017). Finding Mungo Man: The moment Australia's story suddenly changed. The Guardian. Retrieved from https://www.theguardian.com/australia-news/2017/nov/14/finding-mungo-man-the-moment-australias-story-suddenly-changed

Dorey, F. (2015). The spread of people to Australia. Retrieved from https://australianmuseum.net.au/the-spread-of-people-to-australia

Hiscock, P. (2008). Archaeology of ancient Australia. New York: Routledge.

Weule, G., & James, F. (2017, July 20). Indigenous rock shelter in top end pushes Australia's human history back to 65,000 years. ABC News. Retrieved from http://www.abc.net.au/news/science/2017-07-20/aboriginal-shelter-pushes-human-history-back-to-65,000-years/8719314

Williams, E. (2013, January 11). Explainer: What is an isotope? The Conversation. Retrieved from https://theconversation.com/explainer-what-is-an-isotope-10688

Wood, R. (2012, November 28). Explainer: What is radiocarbon dating and how does it work? The Conversation. Retrieved from https://theconversation.com/explainer-what-is-radiocarbon-dating-and-how-does-it-work-9690