73 layers of ash show one Australian cave hosted the same fire practice for thousands of years

Cloggs Cave in southeastern Australia was used across roughly 25,000 years, and the study’s authors present the burnt plant traces as evidence of one of the world’s longest-running ritual traditions. Nothing about the cave itself explains the grass. “No plants grow inside the cave due to a lack of light,” Grono said, which means every stem that turned to ash was a deliberate delivery from outside.

What the ash layers record

In the cave, sediment covered each burnt layer in turn, so the sequence stayed intact rather than being stirred together. The team dated the deposits with optically stimulated luminescence and accelerator mass spectrometry carbon dating.

The upper parts of two excavation pits, measuring 1.5 metres and 2.3 metres deep, contained 73 thin layers of ash laid down between about 4,400 and 1,600 years ago. That is a repeated fire practice recurring across roughly 2,800 years, which the ScienceDaily release describes as consistent with GunaiKurnai traditional practices of using ash to perform magic and rituals. Those 73 layers sit inside the longer span of use, not on top of it. The burnt plant material appears in the dated deposits throughout, with up to 18% of the microscopic plant fragments showing signs of burning or melting, according to the Frontiers news release that accompanied the study. The researchers read that as evidence that burning happened across the whole of the roughly 25,000 years, while the best-preserved run of individual ash events belongs to the later period. Dr Elle Grono, a postdoctoral researcher at the Australian National University, and a team from Australia, France and New Zealand have shown that people repeatedly carried grasses into Cloggs Cave on GunaiKurnai Country in southeastern Australia and burned them there, a fire practice the Frontiers release says took place over the past 25,000 years. Within the ashy layers the excavators also found something they had not expected: a standing stone 28 centimetres high, set upright around 2,000 years ago. The study concludes it was placed for ritual purposes, and the burnt plant fragments came from the ash surrounding it.

Phytoliths and the choice of grass

Pollen is a poor guide in a dark cave, because wind and insects can blow it in. Grono’s team instead studied phytoliths, microscopic silica bodies that form inside plant tissue and survive long after the plant itself has rotted away. In the study published in Frontiers in Environmental Archaeology, they concentrated on half-burnt phytoliths from the ashy layers. Grono explained that unburnt ones could have arrived by animals such as possums, but burnt ones could only have come from people.

The team sorted thousands of phytoliths into 29 types spanning grasses, herbs and woody plants. Grasses made up as much as 97% of the total. Cool-climate Pooideae and warm, humid-climate Panicoideae were common, while drought-tolerant Chloridoideae were less frequent, and herbs and woody plants were rare.

The selectivity is the striking part. Phytoliths came from stems, leaves, flowers and roots, which indicates whole grasses were carried in, inedible parts included, and the diverse riparian forest and open woodland species growing near the cave barely appear. “The Old Ancestors selected whole grasses from the wider landscape,” Grono said, gathering plants that grew a short distance away rather than whatever lay closest to the entrance.

GunaiKurnai knowledge and the ritual reading

The interpretation rests on more than the ash. The GunaiKurnai are the Aboriginal nation and traditional custodians of Gippsland and the southern Victorian Alps, and nineteenth-century accounts and oral traditions describe caves in their country as places where learned practitioners called mulla-mullung performed magic, healing and cursing. Professor Bruno David of Monash University, who co-led the 2019 and 2020 excavations with the GunaiKurnai Land and Waters Corporation, said the burning is “consistent with GunaiKurnai traditional practices of using ash to perform magic and rituals.”

Uncle Russell Mullett, a GunaiKurnai elder and co-author, told ABC News that these healers were “doctors” sought out by families for cures, though they also held powers that could harm people. The corporation requested the excavations, and community representatives took part in the research design, fieldwork, interpretation and communication of the findings. ABC News added that digging at the site in the 1970s had happened without the permission of traditional owners. David has also suggested that the ash may have been used to track the footsteps of people entering the cave, including spirit beings. Deeper, older deposits held fat-smeared, trimmed sticks from Casuarina trees, which the study treats as a sign of other rituals involving woody plants.

How far the evidence reaches

That claim deserves care. The sources show repeated, selective grass burning across thousands of years, and they link it to documented GunaiKurnai ash practice. They do not show that one fixed rite was performed unchanged, and the ritual reading is an inference from the ash, the stone and cultural records rather than a direct observation. Caroline Spry, a La Trobe University archaeologist not involved in the work, described the authors’ reasoning as a careful interpretation, and called the grass evidence exciting.

Dating also thins out with depth. ABC News reported that the oldest securely dated samples are 24,000 to 25,800 years old, and that rockfall before about 25,000 years ago mixed earlier deposits. David said the precise age of those deeper levels is less secure. The count of 73 layers therefore describes the later, well-resolved stretch, while the full 25,000-year story depends on fewer, coarser dates. The full paper, with its dated pits and phytoliths, is archived under the study’s DOI, which lists Grono, David, Mullett and eight other authors.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.

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