Light and shade: how the natural ‘glazes’ on the walls of Kimberley rock shelters help reveal the world the artists lived in

Helen Green, The University of Melbourne and Damien Finch, The University of MelbourneThe Kimberley region is host to Australia’s oldest known rock paintings. But people were carving engravings into some of these rocks before they were creating paintings.

Rock art sites on Balanggarra Country in the northeast Kimberley region are home to numerous such engravings. The oldest paintings are at least 17,300 years old, and the engravings are thought to be even older — but they have so far proved much harder to date accurately.

Cupules, or circular man-made hollows, ground into a dark mineral coating at a rock art site on the Drysdale River, Balanggarra country.
Photo by Damien Finch

But in research published today in Science Advances, we report on a crucial clue that could help date the engravings, and also reveal what the environment was like for the artists who created them.

Some of the rocks themselves are covered with natural, glaze-like mineral coatings that can help reveal key evidence.

What are these glazes?

These dark, shiny deposits on the surface of the rock are less than a centimetre thick. Yet they have detailed internal structures, featuring alternating light and dark layers of different minerals.

Our aim was to develop methods to reliably date the formation of these coatings and provide age brackets for any associated engravings. However, during this process, we also discovered it is possible to match layers found in samples collected at rock shelters up to 90 kilometres apart.

Radiocarbon dating suggests these layers were deposited around the same time, showing their formation is not specific to particular rock shelters, but controlled by environmental changes on a regional scale.

Dating these deposits can therefore provide reliable age brackets for any associated engravings, while also helping us better understanding the climate and environments in which the artists lived.

Marsupial tracks scratched into a glaze like coating at a rock art shelter in the north east Kimberley.
Photo by Cecilia Myers/Dunkeld Pastoral Company; illustration by Pauline Heaney/Rock Art Australia

Microbes and minerals

Our research supports earlier findings that layers within the glaze structure represent alternating environmental conditions in Kimberley rock shelters, that repeated over thousands of years.

Our model suggests that during drier conditions, bush fires produce ash, which builds up on shelter surfaces. This ash contains a range of minerals, including carbonates and sulphates. We suggest that under the right conditions, these minerals provided nutrients that allowed microbes to live on these shelter surfaces. In the process of digesting these nutrients, the microbes excrete a compound called oxalic acid, which combines with calcium in the ash deposits to form calcium oxalate.

A: dark coloured, smooth mineral coating at a Kimberley rock shelter; B: alternating layering, as seen in the field; C: alternating layering as seen in a cross-sectioned coating under a microscope.
Photos by Cecilia Myers; microscope image by Helen Green

As this process repeats over millennia, the minerals become cemented together in alternating layers, with each layer creating a record of the conditions in the rock shelter at that time.

Samples of the glazes were collected for analysis in close collaboration and consultation with local Traditional Owners from the Balanggarra native title region, who are partners on our research project. Using a laser, we vaporised tiny samples from the coatings to study the chemical composition of each layer. The dark layers were mostly made of calcium oxalate, while lighter layers contained mainly sulphates. We propose darker layers represent a time when microbes were more active and lighter layers represent drier periods.

Read more:
How climate change is erasing the world’s oldest rock art

Linking the layers

These dark calcium oxalate layers also contain carbon that was absorbed from the atmosphere and digested by the microbes that created these deposits. This meant we could use a technique called radiocarbon dating to determine the age of these individual layers.

Using a tiny drill, we removed samples from distinct dark layers in nine glazes collected from different rock shelters across the northeast Kimberley.

A: micro-drilling samples from individual layers for radiocarbon dating; B: Laser ablation maps showing the distribution of the element calcium within the different layers; C: radiocarbon dating of individual layers identified four key growth periods.
Photo by Andy Gleadow; illustration by Pauline Heaney

Despite coming from different locations, these layers all seem to have been deposited at the same time, during four key intervals spanning the past 43,000 years.

This suggests the formation of each layer was determined mainly by shifts in environmental conditions throughout the Kimberley, rather than by the distinct conditions in each particular rock shelter.

The records held by these glazes over such a large time period – including the most recent ice age – means they could help us better understand the environmental changes that directly affected human habitation and adaptation in Australia.

Hypothetical example of how layered mineral coatings can be used to date engraved rock art in Kimberley rock shelters.
Pauline Heaney

Stories in stone

Research we published earlier this year shows how the subjects painted in early Kimberley rock art changed from mostly animals and plants around 17,000 years ago, to mostly decorated human figures about 12,000 years ago.

Read more:
This 17,500-year-old kangaroo in the Kimberley is Australia’s oldest Aboriginal rock painting

Other researchers have discovered that during this 5,000-year period there were rapid rises in sea level, in particular around 14,500 years ago, as well as increased rainfall.

We interpret the change in rock art styles as a response to the social and cultural adaptations triggered by the changing climate and rising sea levels. Paintings of human figures with new technologies such as spear-throwers might show us how people adapted their hunting style to the changing environment and the availability of different types of food.

By dating the natural mineral coatings on the rock surfaces that acted as a canvas for this art, we can hopefully better understand the world in which these artists lived. Not only will this give us more certainty about the position of particular paintings within the overall Kimberley stylistic rock art sequence, but can also tell us about the environments experienced by First Nations people in the Kimberley.

We thank the Balanggarra Aboriginal Corporation, the Centre for Accelerator Science at the Australian National Science and Technology Organisation, Rock Art Australia and Dunkeld Pastoral Co for their collaboration on this research._The Conversation

Helen Green, Research Fellow, The University of Melbourne and Damien Finch, Research fellow, The University of Melbourne

This article is republished from The Conversation under a Creative Commons license. Read the original article.


Climate science is now more certain than ever. Here’s how it can make a difference in Australian court cases


Laura Schuijers, The University of Melbourne

On Monday, the Intergovernmental Panel on Climate Change (IPCC) released its long-awaited report on the physical impacts of climate change. It painted a terrifying picture of a warming planet increasingly subject to extreme weather events.

If there’s a silver lining to the 3,900 pages of gloom, it’s that there’s still time to avert the worst damage if global emissions are rapidly cut. So what happens if the Australian government continues to lag?

Well, while foreign countries can’t sue Australia under the Paris Agreement, they can apply political and economic pressure, such as through publicly calling our leadership out and applying carbon border adjustments.

But we’re also seeing another important and growing trend: domestic climate litigation.

In fact, Australia is second only to the US in terms of the volume of climate change cases brought before the courts.

In the last few years in particular, we’ve seen Australian cases succeed in influencing action. With this new IPCC report, climate science is more certain than ever, making it more likely this trend will continue.

Avoiding catastrophic impacts

The IPCC report concluded that escape from climate change is no longer possible. And, the report indicates, Australia will be badly hit.

It’s believed our best achievable scenario is to reach net-zero emissions by midcentury, on a global scale. This will hopefully equate with an around 1.5℃ temperature rise above preindustrial levels, which is what the IPCC says is our maximum to avoid catastrophic impacts.


Although some countries have made pledges under the Paris Agreement in line with this goal, Australia, we know, is shirking. If all countries adopted targets as weak as ours, global warming would be in the order of 4.3-4.5℃.

While climate change is caused by the actions of many, some are in better positions than others to mitigate it. So it’s no surprise businesses, financial institutions, and governments have been the prime targets of a new wave of litigation.

Courtrooms are changing

Fifteen years ago, the Australian federal court considered the climate change impacts of one particular coal project to be “speculative” and “minute”, citing a “paucity” of detail about the possibility of coal contributing to climate change.

But the situation is changing, and courts are changing with it. One of the reasons for the about-face is the progression of climate science and the availability of new information from advanced modelling. The work of the IPCC is instrumental to this.

Read more: This is the most sobering report card yet on climate change and Earth’s future. Here’s what you need to know

A couple of recent examples of cases show how climate science is becoming more influential in Australian court decisions.

In a case heard this week between the Bushfire Survivors group and the NSW Environmental Protection Authority, a NSW court allowed evidence to be presented from former Australian Chief Scientist Penny Sackett on climate change impacts.

It is the first time this kind of evidence has been allowed in a case about the alleged failure of an authority (the EPA) to perform a statutory duty (the regulation of greenhouse gases). On Tuesday, the Bushfire Survivors asked the court to allow her to comment on the IPCC’s sixth report.

And in a landmark case in May against the federal environment minister, the federal court found Australia’s young people are at high risk of suffering personal injury from climate change in their lifetime, including death and hospitalisation.

The judge was considering a coal mine approval. He said even though one coal mine won’t single-handedly cook the planet, it could serve as the proverbial straw that broke the camel’s back, given climate science tells us irreversible “tipping points” may be reached one day, and it could be soon.

The judge cited the IPCC’s findings, recognising the IPCC as the authority on climate change, and called on one of its authors as an expert witness.

Read more: In a landmark judgment, the Federal Court found the environment minister has a duty of care to young people

How will climate science play into future cases?

What’s happening in Australian courts is part of a bigger global trend.

It’s not just that the volume of cases is increasing, cases are also becoming more creative, exploring new avenues to hold polluters and decision makers to account. These cases are more likely to succeed where a link between actions and impacts can be supported with evidence.

In a case against Shell in May this year, a Dutch court ordered Shell to reduce its emissions by 45% by 2030, relative to 2019 emissions. To reach this figure, the court extensively cited the past work of the IPCC. It concluded Shell’s corporate policy was “hazardous and disastrous” and “in no way consistent” with the global climate target to prevent a dangerous climate change for the protection of people, the human environment and nature.


There are many ways climate science will be instrumental to the success of future cases. The evidence released so far by the IPCC shows us different warming scenarios under climate change, each depending on the actions we take now and in the near future.

Chapter 3 of Monday’s IPCC report is dedicated to spelling out the now “unequivocal” influence of humans. This type of evidence could support cases seeking to force government action, as well as cases against businesses for failing to disclose and mitigate climate risk, and for greenwashing.

Read more: Communicating climate change has never been so important, and this IPCC report pulls no punches

Next year, the IPCC will release its findings on impacts, adaptation, and vulnerability. This could support cases relating to fire, flood, and sea-level rise, including human rights cases, property, planning, and insurance cases.

Climate change will unfortunately be costly, and litigation can help determine who should take action, and who should pay.

The more Australia’s governments and businesses lag on climate change, the more litigation we are likely to see. And, the greater the extent leadership decisions are at odds with the science, the stronger plaintiffs’ cases will be.



The Conversation


Laura Schuijers, Research Fellow in Environmental Law, The University of Melbourne

This article is republished from The Conversation under a Creative Commons license. Read the original article.