The Cave Where Fire Was Not About Heat for 25,000 Years

For at least 25,000 years, people entered Cloggs Cave carrying whole grass plants. Not to eat. Not to build cooking fires. The leaves, stems, and flowering parts of the grasses were not needed for any of the practical purposes that normally explain why plant material turns up in an archaeological site. They were needed for something that left a different kind of trace: repeated, low-temperature burning that produced ash and smoke rather than heat, in a secluded and deliberately chosen underground space, across a period of time that dwarfs the entire recorded history of every other civilisation on earth.

A new study published in Frontiers in Environmental Archaeology has found the microscopic evidence of that practice preserved across 25,000 years of deposits at Cloggs Cave in GunaiKurnai Country in southeastern Australia. The research was conducted in direct partnership with the GunaiKurnai Land and Waters Aboriginal Corporation, whose members are listed as co-authors of the paper, and whose traditional knowledge about ceremonial practice informs the interpretation of what the evidence means.

Reading Plants in Microscopic Silica

The method at the heart of the study is phytolith analysis. Phytoliths are microscopic silica structures that form inside plant cells during a plant’s lifetime, taking on shapes specific to the tissues in which they develop. When a plant burns or decays, the organic material disappears but the silica structures can survive in soil or sediment for extraordinarily long periods, preserving information about what kinds of plants were present and which parts of those plants the silica came from.

Researchers examined phytoliths from deposits spanning the full 25,000-year sequence inside Cloggs Cave. They identified structures from leaves, stems, and the flowering parts of grass plants, not only from seeds. That distribution is what pointed toward whole plants being brought into the cave. If people had been collecting grasses for food, they would typically have focused on the seed-bearing parts. Carrying the entire plant, including portions with no nutritional value, into a confined underground space required a different kind of reason.

Blackened and heat-altered phytoliths appeared throughout the stratigraphic sequence. To separate human burning from any plant material that animals might have introduced naturally, the researchers also analysed phytoliths from preserved possum droppings recovered from the same deposits. The blackened phytoliths were entirely absent from the possum samples. The heat-altered material was attributable to human fire use, and it was present across the full 25,000-year timespan of the cave’s archaeological record.

Fires That Made Ash, Not Heat

The character of the fires is as significant as their presence. Dozens of thin ash layers have been documented across the cave’s stratigraphy, and many contain little charcoal. That ratio is informative: conventional cooking fires or fires built for warmth produce substantial charcoal alongside ash. A fire that generates mainly ash and minimal charcoal is burning softer, more easily combusted fuel at relatively low temperatures.

The phytolith analysis supports that inference. Grass remains dominate the assemblage. Evidence associated with woody plants is scarce. Only a limited proportion of the phytoliths showed signs of blackening or melting consistent with high-temperature combustion. The researchers concluded that grasses were likely selected over wood as the preferred fuel for these fires, producing shallow sheets and lenses of ash across the cave floor without the sustained intense heat that cooking or extended warmth fires would require.

A fire built to generate ash and smoke, from selected soft vegetation, in a narrow, enclosed underground chamber, is not a domestic fire. It is something else.

What GunaiKurnai Traditions Say

The word mulla-mullung refers in GunaiKurnai culture to individuals, both men and women, who possess specialised knowledge connected with healing, magic, cursing, and the spiritual world. They are not simply medical practitioners or religious leaders in the sense those terms carry in other traditions. They are specialists in a form of knowledge and power that does not separate the physical from the spiritual, the body from the country, or the human from the world of non-human forces that share the landscape.

Historical accounts of GunaiKurnai ceremonial practice record the use of grass, ash, and charcoal in initiation, healing, and spiritual performance. The smoke produced by burning selected vegetation in enclosed or controlled spaces carried meaning that extended well beyond the practical properties of combustion. The ash that remained after the fire was not simply waste. It was a product with its own significance, created through a deliberate process in a deliberately chosen place.

The new study cannot identify the precise intent of each ancient fire. The archaeological record does not preserve that level of specificity across 25,000 years. What it does preserve, with unusual clarity, is the pattern: selected vegetation, controlled burning, ash-rich remains, in a secluded underground space repeatedly visited over an immense period of time. That pattern aligns closely with a cultural framework in which what was burned, where it was burned, and what was produced by the burning all carried meanings the researchers are careful not to reduce or overstate.

Earlier Finds in the Same Cave

The phytolith evidence extends and strengthens a picture that earlier discoveries had already begun to outline. Two miniature fireplaces inside Cloggs Cave, dated to approximately 11,000 and 12,000 years ago, each contained a carefully prepared Casuarina stick coated with animal or human fat. These features were reported in earlier publications and interpreted as evidence for specialised practice at the site. Around 2,000 years ago, vegetation was burned near a small standing stone inside the cave over a period of roughly four centuries.

Taken individually, each of these finds is unusual. Together with the 25,000-year phytolith record, they suggest a site that was used, again and again across a vast span of time, by people with specialised cultural authority, in ways that involved the same basic elements: selected plants, fire, smoke, ash, darkness, and a cave whose narrow passage and enclosed chamber created a sensory environment unlike anything in the open landscape outside.

A Tradition Longer Than Most of Human History

The 25,000-year span of the Cloggs Cave record exceeds the combined duration of every major ancient civilisation that most people can name. The pyramids of Egypt are roughly 4,500 years old. The earliest Mesopotamian cities are around 6,000 years old. The Cloggs Cave evidence for plant selection and ceremonial burning begins more than four times further back than either.

That depth does not make the practice less specific or less human. It makes it more so. What the phytolith study reveals is not a curiosity or an anomaly but a tradition, continuous and renewed across tens of thousands of years, in one place, on one country, by people who knew what the cave was for and returned to it accordingly. The GunaiKurnai Land and Waters Aboriginal Corporation’s participation as co-author of this research places that continuity at the centre of the science, rather than treating living knowledge as background context for what the sediment contains.

The fires inside Cloggs Cave were not built for heat. They were built for something that required ash, smoke, darkness, and a very long understanding of what this place was.

Sources

Grono, E., David, B., Mullett, R., Stevenson, J., Petchey, F., Delannoy, J-J., McDowell, M.C., Miller, D.J., Morley, M.W., Freslov, J., Jenkin, D., and GunaiKurnai Land and Waters Aboriginal Corporation (2026). Phytoliths from Cloggs Cave, GunaiKurnai country (southeastern Australia) reveal the gathering of whole grasses for burning practices inside the cave. Frontiers in Environmental Archaeology, 5:1871928. https://doi.org/10.3389/fearc.2026.1871928